Why Fast?

Part One – Weight Loss“When a person has nothing to eat, fasting is the smartest thing he could do.” – Herman

Hesse, Siddhartha.

I like that quote. It’s making (non-caloric) lemonade out of lemons, and for all the transcendental

insights contained in Hesse’s book, this line strikes me as a really cool, no-nonsense way to make the

best out of a bad situation. No doubt about that. But how useful is it, really, to today’s readers? Very

few of us ever have “nothing to eat.” On the contrary, food is ever at our beck and call, with very little

effort required to obtain it. Actually, that’s not completely true. Processed junk and fast food is readily

available, while the good stuff – fresh meat and veggies, actual, you know, food - requires prep work,

cooking, time, and the doing of dishes. But the main point stands: we rarely go without.

That doesn’t mean the quote is useless. In fact, with a few slight modifications, it becomes extremely

effective weight loss advice. Check out my version:

“When a person has had too much to eat, fasting is the smartest thing he could do.” – Mark

Sisson, Mark’s Daily Apple.

If that sounds harsh or even unrealistic, consider the story of the Scotsman. Back in 1965, an obese

Scotsman of 27 years and 456 pounds came to the Department of Medicine in Dundee, Scotland, with

a problem. He needed to lose weight. A (1/8 of a) ton of it. The doctors suggested maybe not eating

for a few days could help. It was just an offhand recommendation, but our Scotsman (known only as

“AB”) really took to it. He stayed at the hospital for several days, taking only water and vitamin pills

while undergoing observation to ensure nothing went wrong. When his time was up, he continued the

fast back at home, returning to the hospital only for regular monitoring. After a week, he was down five

pounds and feeling good. His vitals checked out, blood pressure was normal, and though he had

lower blood sugar than most men, he didn’t seem particularly impaired by it. The experiment

continued… for 382 days.

Yes, AB fasted for 382 days, drinking only water and taking vitamin, potassium, and sodium

supplements. All told, he lost 276 pounds, reaching his target weight of 180 pounds and maintaining

the bulk of his weight loss. Over the five following years of observation, AB regained just sixteen

pounds, putting him in excellent, but underpopulated territory (at least 80% of dieters eventually

regain all the lost weight). Other doctors paid attention. Maybe it was the fact that it was the 60s, and

all sorts of crazy stuff was going on – rebellion in the air, good music being made, a war in Vietnam,

Ken Kesey and his Merry Pranksters blazing across the U.S. in a beat-up school bus, spreading the

good weird word, Kevin Arnold and a young Marilyn Manson coming of age in Anytown, USA – but for

whatever reason, placing obese patients on extended and short-term fasts became relatively common

practice.

But could this work for the average person looking to lose weight without submitting to constant

medical observation?

Absolutely. Study after study shows that whatever you want to call the protocol – intermittent

fasting, fasting, alternate day fasting, or alternate day caloric restriction – it works very well for

weight loss. A few recent ones:

In non-obese patients, alternate day fasting increased fat oxidation and weight loss. In obese patients, alternate day fasting was an effective way to lose weight; dietary adherence

remained high throughout. In young overweight women, alternate day fasting was just as effective as caloric restriction at

causing weight loss, and adherence to the former was easier than to the latter.

So, yes: it works. But does fasting work solely through caloric restriction, or is it doing something

special?

That’s the real question. There’s no question that fasting causes weight loss through caloric

restriction. Obviously, when you don’t eat anything, your body turns to its own stored energy reserves,

reserves that take up physical space and have mass. Depletion of those energy stores reduces mass

and thus weight. Total and absolute caloric restriction. That’s elementary stuff and the studies from

the 1960s show that.

To dig a bit deeper, let’s look at how weight loss occurs during a fast. I’ll stick to research involving

humans only (sorry, rodent personal trainers).

Secretion of growth hormone, one of the premier fat burning hormones, increases during a

fast. In a five-day fasting protocol, men experienced increased GH secretion on day one and day

five (the only two days where GH was measured). A later study showed that during two-day fasting

sessions, growth hormone secretions increased in both frequency and intensity in men. They

experienced more frequent GH bursts and each burst secreted a higher mass of GH. A more recent

study found that 24-hour fasts increased GH by 1300% in women and almost 2000% in men.

Fasting decreases fasting insulin levels. The presence of insulin inhibits lipolysis, the release of

stored triglycerides (body fat). Without lipolysis actually releasing stored body fat, it’s rather difficult to,

well, burn that body fat for energy. During a fast, fasting insulin decreases and lipolysis increases.

This insulin-blunting aspect of fasting quite literally allows the fast to be successful, because without

the ability to access stored body fat for energy, making it through a period of zero caloric intake will be

nigh impossible.

Fasting improves insulin sensitivity. 20-hour fasts were enough to improve insulin sensitivity in

men.

Fasting increases the catecholamines,

both adrenaline (epinephrine) and noradrenaline (norepinephrine). Both catecholamines increase

resting energy expenditure during a fast, and guess where your fasting body finds the energy to

expend? From body fat. Catecholamines activate hormone sensitive lipase present in adipose tissue,

spurring the release of said fat. This makes intuitive sense, doesn’t it? If you’re hungry in the wild, you

need to hunt (or gather, or fish, or somehow procure food) and you need energy to do it. The

catecholamines help provide some of that energy while burning fat in the process.

Hmm, notice anything? All those mechanisms dealt with fat burning specifically. While there may be

some weirdo out there who’s interested in reducing bone mineral density and muscle mass while

maintaining fat tissue, I would wager that what most people mean by “weight loss” is “fat mass loss.”

From the stuff I just linked, it looks like fasting burns fat, rather than just weight. But what about

Conventional Wisdom which claims that fasting increases muscle wasting – maybe because your

body will totally recognize the lethal nature of all that arterycloggingsaturated animal fat and choose to

break down muscle instead? Is it true?

Let’s go to the research:

In one study, normal weight subjects ate just once a day without reducing overall caloric intake.

Weight didn’t change, which isn’t really surprising, but body composition did change – and for the

better. Body fat decreased and lean weight increased (in addition to a bunch of other beneficial

changes) without an overall reduction in calories.

A recent review of the relevant literature found that while fasting and caloric restriction are

“equally as effective in decreasing body weight and fat mass,” fasting is “more effective for

the retention of lean mass.”

In closing…

It appears that fasting “works” in several different ways:

1. It decreases caloric intake. In order to lose weight, you need a caloric deficit. That really isn’t in

contention here, folks.

2. It increases fat oxidation while sparing lean mass. Since what we’re trying to do is lose fat

(rather than just “weight”), the fact that fasting increases hormones that preferentially burn fat and

decreases hormones that inhibit fat burning is extremely desirable.

3. It improves adherence. In most of the studies surveyed, participants found fasting to be an

extremely tolerable way to diet, especially when compared to outright caloric restriction. Even AB, the

fasting Scotsman, reported very little difficulty throughout his 382 day fast. If fasting is easier for you

than trying to laboriously count calories, fasting is going to be the more effective weight – er, fat – loss

method.

All in all, fasting is an effective way to lose body fat. It’s not the only way, and it isn’t “required” for

Primal weight loss, but many in the community have found it to be very helpful and the literature backs

them up. If you’re looking to jumpstart your fat loss, fasting may be just the ticket. To get some ideas,

be sure to check out my post on various fasting methods.

In subsequent installments, I’ll highlight some of the other benefits of fasting. There are a ton, and

new research is being released all the time, so I expect I’ll have a lot to discuss. Until then, I’d like to

hear about your experiences with fasting for fat loss. Has it worked? Has it failed you? Let us know in

the comment section!

Part Two – Cancer

“Everyone has a physician inside him or her; we just have to help it in its work. The natural healing force within each one of us is the greatest force in getting well. Our food should be our medicine. Our medicine should be our food. But to eat when you are sick is to feed your sickness.” – Hippocrates

and:

“Instead of using medicine, rather fast a day.” – Plutarch

or even:

“No kibble today, thanks. I’m feeling a bit under the weather.” – Fido

For thousands upon thousands of years (during most of which overweight, let alone obese, people

were fairly rare), therapeutic fasting was a common protocol for the healing of many a malady. From

famous sages like Plato, Aristotle, and the aforementioned Hippocrates and Plutarch to cancer

patients unable to eat during chemotherapy to pet dogs and cats who suddenly lose once-voracious

appetites upon falling ill, it seems like the natural response to – and perhaps therapy for – major

illness is to stop eating for a while.

Now, “natural” is not always good. “Is” does not necessarily imply “ought.” But I think the persistence

of this phenomenon throughout nature demands that we look a little more closely into whether or not

there’s something to it. From babies putting items they found on the ground into their mouths to

introduce novel bacteria to their bodies, to weight lifters craving meat after a hard workout to

introduce protein to their hungry muscles, to pregnant women experiencing strong food aversions to

minimize the chance of introducing a toxin or poison to the growing fetus, I’m generally of the opinion

that there’s usually a physiological explanation for most of our odd cravings and behaviors. I see no

reason why a sudden lack of appetite wouldn’t have a similar explanation – especially one that

transcends species. What if skipping meals for a day or two kickstarted internal healing in some way?

Is that really so outlandish? You already know where I stand on the importance of lessons

learned from watching our animal companions, and I think this time is no different.

Luckily for us, we aren’t just flailing around and making guesses. Modern science has deigned

research into the phenomenon, particularly regarding cancer, worth pursuing. According to Valter

Longo, a cancer researcher from USC, “normal cells” go into survival mode during starvation. They

display “extreme resistance to stresses” until the “lean period” ends, much like an animal in

hibernation mode. Cancer cells, on the other hand, are always “on.” Their “goal” is to grow and

reproduce and consume resources. For cancer cells, there is no novel survival mode to switch on. If

this is the case, fasting should both improve our resistance to cancer and our body’s ability to survive

it (and the treatments used against it, like chemotherapy).

Though human trials are scant (you can’t exactly inject people with cancer cells and then try out

different therapeutic protocols, the animal research is intriguing. Let’s take a look into the literature,

shall we?

Animal Trial

In one of the earliest studies, forty-eight rats were split up into two groups of twenty-four. One group

ate ad libitum for a week, while the other group underwent alternate day fasting. After one week of the

various dietary protocols, both groups were injected with breast cancer. At nine days post-injection, 16

of 24 fasted rats remained alive, while just five of 24 ad-libitum fed rats lived. At ten days post-

injection, only three of the 24 ad libitum-fed rats survived; 12 of the 24 fasted rats remained alive.

Pretty large disparity, right?

That was in 1988. It wasn’t until the late 90s that more promising research was undertaken. That’s

when Longo began studying in earnest the phenomenon of increased cellular resistance to oxidative

stress during fasting. Figuring that since chemotherapy exerts its effects on cancer by inducing

oxidative stress (to all cells, not just cancerous ones), and fasting triggers survival mode in normal

cells but not cancer cells, he conducted a study on mice to determine whether fasting protected the

healthy, normal cells from chemotherapy’s side effects while leaving the cancer cells sensitive to the

treatment. Tumor-ridden mice were either fasted or fed normally 48 hours prior to a large dose of

chemotherapy. Half of the normally-fed mice died from chemotherapy toxicity, while all of the fasted

mice survived (PDF). Furthermore, fasting did not improve the survival rate of cancerous cells,

meaning it only protected normal, healthy cells.

Research has continued. Longo found that “starvation-dependent stress” protects normal cells, but

not cancer cells, against the effects of chemotherapy. Even a “modified” alternate day fasting

regimen, in which mice were given 15% of their normal calories on “fasting” days, reduced

proliferation rates of tumor cells. This “85%” fasting regimen was even more effective than the full

100%. Andmost recently, Longo et al found that fasting both retarded the growth of tumors while

sensitizing cancer cells to the effects of chemotherapy – across a wide range of tumor types. Most

importantly, they concluded that fasting could “potentially replace or augment” certain

existing chemotherapy regimens! That’s not some crazy fad diet guru spouting off about ancient

traditional wisdom, folks. That’s a cancer researcher.

Human Trial(s)

There has been just one of which I’m aware: a 2009 case study that delivered promising results. Ten

cancer patients – four with breast cancer, two with prostate cancer, one each with ovarian, lung,

uterine, and esophageal cancers – underwent fasting prior to and after chemotherapy treatment.

Fasting times ranged from 48-140 hours prior to and 5-56 hours after; all were affective at reducing

side effects of chemotherapy.

In the first case, a 51-year old woman with breast cancer did her first round of chemotherapy in a

fasted state of 140 hours. Other than dry mouth, fatigue, and hiccups, she felt well enough to go to

work and resume her normal daily activities. For the subsequent two rounds, she did not fast and

instead ate her normal diet, and the side effects were extremely pronounced – severe fatigue,

diarrhea, weakness, abdominal pain, nausea – and prevented her from returning to work. For her

fourth round of chemotherapy, she fasted, and the side effects were again minimized. And it wasn’t

just the subjective effects that improved with fasting, but also her physiological markers. Total white

blood cell, absolute neutrophil counts, and platelet counts were all highest after the fasting regimens.

More human trials are underway, however. Hopefully we’ll eventually know whether the loss of

appetite commonly reported during chemotherapy treatment is a bug or actually a built-in feature (I’m

leaning toward the latter, personally).

Other Possible Protective Mechanisms of Prevention

Improved insulin sensitivity. As I showed in last week’s post on fasting and weight loss, intermittent

fasting improves insulin sensitivity and reduces insulin resistance. Insulin resistance has been linked

to several cancers, including prostate, breast, and pancreatic. Metabolic syndrome, which fasting

seems to help prevent and reduce, is linked to cancer in general.

Autophagy. While autophagy – the process by which cells “clean up” cellular “garbage” – has

a complex relationship with cancer, it’s generally a positive process that protects cells from

excessive oxidative stress. Fasting has been shown to induce “profound” neuronal autophagy, as well

as general autophagy.

Fasting versus caloric restriction.

It’s true that caloric restriction appears to offer anti-cancer benefits, but there are a couple ways in

which fasting might be superior:

1. Fasting (acute bouts of caloric restriction) is easier than CR (chronic caloric restriction) for

most people. As I mentioned in last week’s post, fasting – for some – is just an easier, more natural,

more effortless way to reduce your calorie intake. That can pay huge dividends when it comes to

weight loss, and it appears likely that it will help with cancer, too. If fasting is easier than constantly

counting your calories, fasting is going to work better.

2. Fasting is more effective in a shorter amount of time. Whereas studies on caloric restriction and

cancer employ weeks- and months-long CR regimens, studies on fasting and cancer employ hours-

and days-long fasting regimens. In most cases, fasting just seems to require far less time to be

effective.

It’s an exciting time for fasting and cancer research. While it’s still viewed in most circles as an

“alternative” modality, fasting is now being seriously considered as a possible treatment (both adjunct

and even primary) for various cancers, including breast and prostate. I can’t wait to see what comes

out in the coming years.

Of course, my own feeling is that fasting is both easier and more effective if you have made the

transition to a Primal Blueprint way of eating. In other words, when you have up-regulated those fat-

burning systems and down-regulated the reliance on glucose, many of the other issues that can make

fasting less appealing to “sugar-burners” tend to go away: cortisol levels out, muscle protein is spared,

hunger subsides naturally and energy is steady.

What does this mean for you – the person who either has cancer and wants to get rid of it or who

doesn’t have cancer and wants to stay that way? Researchers like Valter Longo can’t officially

recommend it to cancer patients, but it seems well-tolerated and basically safe. If you or anyone you

know has cancer, suggest fasting as a possible strategy. As long as a person keeps their oncologist

apprised of the situation and any relevant research on the subject, it might prove helpful. And if you’re

currently cancer-free, consider implementing occasional (intermittent) fasts, just to be safe. I know

research like the stuff I’ve just outlined has convinced me that it’s definitely worth a shot, and there’s

little if any downside.

Part Three – LongevityA time-honored and research-tested way to extend an animal’s lifespan is to restrict its caloric intake.

Studies repeatedly confirm that if, say, a lab mouse normally gets two full bowls of lab chow a day,

limiting that mouse to one and a half bowls of lab chow a day will make that mouse live longer than

the mouse eating the full two bowls. Cool, cool, a longer life is great and all, but what about the

downsides of straight calorie restriction, aside from willfully restricting your food intake, ignoring

hunger pangs, relegating yourself to feeling discontent with meals, and counting calories and

macronutrients obsessively? Are there any others? Sure:

Loss of muscle mass. Humans undergoing calorie restriction often suffer loss of lean muscle mass

and strength, all pretty objectively negative effects (unless you really go for the gaunt “Christian Bale

in The Machinist” look and use a super-strong bionic exoskeleton for all your physical tasks).

Loss of bone mineral density. Humans who calorie restrict in studies also show signs of lower bone

mineral density when compared to humans who lose weight from exercise, particularly in the hip and

spine – the two areas most susceptible to fall-related bone breaks. I wrote about this study some time

ago here.

Oh, and there’s the fact that the act of restricting one’s calories can be mind-numbing,

miserable, and difficult for a great many people, especially if it’s a lifelong pursuit. (Unless, of

course, you eat according to the Primal Blueprint and are fat-adapted. It can make CR not only

tolerable, but a cinch because we become so good at living off stored body fat. We don’t suffer from

sugar lows when we skip meals the way most people who fast do, but I digress.) That’s kind of a

biggie.

What about fasting? In previous installments of this series, I’ve explained how fasting can sometimes

be described as a “short cut” to the benefits of calorie restriction, an easier (and even more effective)

path to the same destination. Studies on fasting/calorie restriction and cancer find that fasting is more

effective in a shorter amount of time (weeks or months versus mere days). Does the same hold true

for longevity? Can fasting also extend lifespan without making us look like a calorie-restricted

monkey?

1945 marks the first real study (PDF) of the effects of intermittent fasting on lifespan in animals.

Beginning at day 42 of their lives, rats were either fasted one day in four, one day in three, or every

other day. All fasted rats, save for the females who were fasted one day in four, lived longer than

control rats on a normal schedule. Although females outlived males in general (like always), fasting

had the greatest effect in males. Male rats did best on every other day fasting; female rats did best on

one day in three fasting. Fasted rats weighed less than control rats, so they likely also ate less, even

though feeding days were ad libitum.

In a 1982 study, mice fed every other day lived 82% longer than mice fed ad libitum every day. No

word on calorie intake.

Another study from 1983 showed that rats fed every other day lived longer and had lower body

weights than rats fed daily and ad libitum. Fasted rats were less active in their youth, but more active

than control rats when adults. The lower body weights in the fasted rats indicate a reduced calorie

intake.

In 2000, female mice who fasted for four consecutive days every two weeks lived for 64 weeks on

average, while normal fed mice lived just 47 weeks. Interestingly, the fasted mice were heavier than

the fed mice throughout the experiment, which indicates that calories weren’t significantly restricted.

Okay, so it looks like fasting promotes longevity, which may be mediated by a reduction in calories.

Provided the faster doesn’t gorge him or herself on the feeding days so much that they make up for all

the missing calories, it should be effective. In other words, fasting promotes longevity in all but the

most ardent of big eaters. I don’t see this as a “gotcha” or a problem, because fasting almost

invariably produces calorie restriction. (I might eat a fairly big meal after a long fast, but I definitely

have never doubled my intake to make up for the fasted day.) In fact, that fasting makes calorie

reduction painless and inadvertent is a highly-touted feature of the practice, and a big part as to why

it’s so effective for people who have failed with traditional calorie restriction.

So, how’s it all work? Is it just the calorie restriction?

Perhaps. One potential pathway by which both fasting and CR increase lifespan is via inhibition of

mammalian target of rapamycin, or mTOR. The mTOR pathway can be said to drive the aging

process. It is necessary for cell growth, like muscle cells (in stable mTOR states) or certain cancer

cells (in overactive mTOR states), and it is highly sensitive to nutrient availability and hormonal

signaling. In mice, feeding rapamycin – a potent inhibitor of mTOR - increases lifespan. Both not

eating (fasting) and lowering potential hormonal messengers (like insulin) also inhibit mTOR

activity by spiking AMPK.  Indeed, in the presence of insulin, mTOR is upregulated. We know from

previous posts that fasting reduces fasting insulin. In insulin resistant people, insulin is chronically

elevated and mTOR is overactive. We also know that fasting reduces insulin resistance and increases

insulin sensitivity, thus normalizing or inhibiting excessive mTOR activity. This kind of mTOR inhibition

also works with CR, but if adherence is easier, side effects are lessened, and AMPK spiking is greater

with total caloric restriction (fasting) than with partial CR, which is the more effective method?

So, it’s starting to look like the longevity benefits of fasting can be attributed to the degree of caloric

restriction. That is, fasting is total caloric restriction, while CR is partial. When you fast, you’re going

whole hog. You’re subjecting yourself to an acute stressor, getting the hormetic benefits, and then

recovering from that stressor by eating normally thereafter (until you do it again). When you calorie

restrict, you’re undergoing a chronic stressor. Day in, day out, you’re worrying about food, restricting

energy and nutrient intake, and there’s really no period of recovery. You’re always residing in a

partially restricted state, drifting from paltry meal to paltry meal. There is no feast. It’s like lifting heavy

and sprinting a few times a week versus jogging a 10k every day. Chronic cardio versus acute, high

intensity exercise.

What about “healthspan”? Can fasting compress morbidity - can it help us in our quest to live long and

drop dead? I mean, let’s face it: who wants to be a frail, skinny-fat centenarian relegated to the bed or

the walker or the wheelchair?

Well, we know that intermittent fasting appears to conserve more lean mass than CR. In

a recent meta-analysis, one group of researchers directly compared studies on calorie restriction to

studies on intermittent fasting and found that while both were good for losing weight, “intermittent CR

may be more effective for the retention of lean mass.” And at the very least, I’d suggest to you that

having better insulin sensitivity, less fat mass, more lean mass, a better-regulated mTOR pathway,

improved blood lipids, better glucose control, and a less restricted diet makes for a better healthspan,

a more enjoyable life, and a reduced risk of dying from the diseases of civilization.

Bottom line: fasting may not work by some magical pathway separate from caloric restriction. It may,

but it hasn’t been established. What we do know is that fasting (whether by inadvertent, enhanced

calorie restriction or whatever else) improves lifespan in lab mammals and improves various health

markers associated with aging and longevity in both humans and animals. Fasting may not give you

an immediate “Life + 25″ boost, and there haven’t been any real lifespan and fasting studies

done on humans (if only we had mice-like lifespans!), but if it makes you less likely to get

obese, diabetes, heart disease, or cancer, you’re less likely to die from those things. The fewer

things you have trying to kill you, the longer you generally live.

Part Four – Brain HealthPretty much every feature of the human body can be found, in some form or another, on other

species. Opposable thumbs? Great for building and using tools, but apes have them, too. Even the

giant panda has an opposable sesamoid bone that works like a thumb. Bipedalism? Helped us avoid

direct mid-afternoon sun and carry objects while moving around the environment (among other

possible benefits), but plenty of other creatures walk upright, like birds and Bigfoot. The human foot?

Okay, our feet are quite unique, but every other -ped has feet (just different types), and they all work

well for getting around. So, what is it that makes us so different from other animals (because it’s got to

be something)?

What truly sets us apart from the rest of the animal kingdom is the human brain. Other animals may

have brains big and complex enough to help them procure food, shelter, and water while processing

and acting on basic sensorial inputs from the environment (“avoid obstacle” or “this smells like food”

or “I am thirsty, where’s the water?”), but they do not share the human brain’s capacity for self-

reflection and symbolic thought. It is the fleshy thinking mass of fatty furrows and gelatinous valleys

sitting atop our spine that gave and gives us art, literature, architecture, agriculture, nuclear power,

syntax, philosophy, advertising, society, this laptop on which I type this post, and the smart phone on

which you read it. In short, our brains make us human. Without them, we wouldn’t be us.

I don’t know about you, but I enjoy being a human. I like contemplating my own existence, being

entertained for hours by strange scribblings on layered sheets of dried and pressed wood pulp, and

playing Ultimate Frisbee, and if I’m going to continue to enjoy those things, I need to protect my brain

and keep it healthy. And if I want to enjoy myself on this planet and experience all it has to offer until I

drop dead, I’m going to need as much brain function as possible (since, you know, the brain handles

all that experimenting stuff) as I age. Luckily, fasting appears to offer three main protective and

therapeutic benefits to the brain:

Fasting Boosts Neuronal Autophagy

I’ve cited this study before, but I’ll do it again because it’s central to the theme of today’s post: “short-

term fasting induces profound neuronal autophagy.” Autophagy, or “self-eating,” is the process by

which cells recycle waste material, downregulate wasteful processes, and repair themselves. Brain

health is highly dependent on neuronal autophagy. In fact, a recent paper shows that deletion of an

“essential autophagy gene” in the hypothalamic neurons of fetal mice resulted in metabolic

derangement (more body fat, poor glucose tolerance) and impaired neuronal development.

Another study shows that disruption of neuronal autophagy induces neurodegeneration. Simply put,

without the process of autophagy, brains neither develop properly nor function the way they should.

Fasting Increases Levels of Brain-Derived Neurotrophic Factor (BDNF)

BDNF is a protein that interacts with neurons in the hippocampus, cortex, and basal forebrain (the

parts of the brain that regulate memory, learning, and higher cognitive function – uniquely human

stuff). It helps existing neurons survive while spurring the growth of new neurons (neurogenesis) and

the development of synapses (lines of communication between neurons). Low levels of BDNF

arelinked to Alzheimer’s, and supplementary BDNF prevents neuronal death, memory loss, and

cognitive impairment in an animal model of Alzheimer’s disease.

Fasting Increases Production of Ketones

Ketone bodies like hydroxybutyrate are famously neuroprotective, and fasting often induces ketosis.

Increased autophagy and BDNF and ketones from fasting sounds awesome, but do they manifest as

actual benefits to neurological health? Let’s see what the research says.

No discussion of fasting and neurological health research is complete (or can even be initiated)

without including Mark Mattson. Mattson, chief neuroscientist at the National Institute on Aging, has

been releasing paper after paper on the neurological effects of intermittent fasting for the past dozen

years, and he’s amassed an impressive body of work that suggests IF can induce neurogenesis and

protect against brain injury and disease. In the following sections, I’ll discuss the evidence – from

Mattson and other researchers – for the beneficial effects of fasting on neurological health across a

spectrum of conditions.

Stroke

The most common type of strokes are ischemic strokes (composing about 88% of all strokes)

- cerebrovascular events in which a blood vessel that supplies blood to the brain is blocked by a clot.

Without blood, the brain can’t get oxygen or nutrients, and (often permanent) brain damage can occur.

In an animal model of ischemic stroke, fasting upregulated BDNF and other neuroprotective proteins,

reduced mortality and inflammation, and increased cognitive health and function. However, it’s worth

noting that fasting was most effective against stroke in young animals, who enjoyed a four-fold

increase in neuroprotective and neurogenerative BDNF. Middle aged mice saw a two-fold increase in

BDNF, while older mice saw no increase. Post-stroke cognitive function had a similar relationship to

age and feeding status; young and middle-aged fasted mice retained far more than old mice and fed

mice. Fasted mice displayed lower levels of inflammatory cytokines, but this effect was also

modulated by age. Overall, fasting increased neuroprotective proteins and decreased inflammatory

cytokines in young and middle-aged mice, thereby reducing the brain damage incurred by stroke.

Brain Trauma

Research indicates that fasting is also effective against physical trauma to the brain. It’s not that

fasting somehow physically repels impending trauma by generating a magical ketone-powered force

field; it’s that fasting reduces the oxidative stress, mitochondrial dysfunction, and cognitive decline that

normally result from brain trauma. Employing one of these contraptions, researchers induced a

“controlled cortical impact” on fasting rats and found that a 24-hour fast (but not a 48-hour fast) was

neuroprotective. Perhaps the reduced appetite that commonly accompanies a concussion is a

protective mechanism rather than an annoying side effect?

Cervical Spine Injury

“Every other day” fasting was neuroprotective following an injury to a rat’s cervical spine. Despite

extensive trauma, fasted rats improved gait pattern, vertical exploration, and forelimb function (all

heavily dependent on brain function). Neuronal integrity was preserved, cortical lesion volume was

reduced, and corticospinal axon (nerve fiber) sprouting increased. The same team performed a similar

study on mice suffering from a spinal cord injury, but had very different results; every other day fasting

failed to confer any neuroprotective or functional benefits to the injured mice whatsoever. How can we

reconcile these apparently contradictory findings? Well, in the rats who experienced neuroprotection,

fasting increased ketone production by 2 or 3 fold. The fasting mice never reached ketosis. Ketosis

was key.

Alzheimer’s disease.

In a mouse model of Alzheimer’s disease, both intermittent fasting and 40% (!) calorie restriction

conferred cognitive and behavioral benefits when compared to mice on the control diet. IF and CR

mice showed higher levels of exploratory behavior, and, when placed in a Morris water maze, found

the escape platform sooner than the control mice. However, only IF mice showed evidence of

protection against synaptic pathology – a hallmark of the disease.

Huntington’s disease.

Huntington’s disease is also characterized by a depletion in BDNF levels. In a rat model of the

disease, intermittent fasting normalized BDNF levels, while regular feeding kept them low. Fasting

rats lived longer and even enjoyed better glucose tolerance than ad libitum fed rats. By all accounts,

fasting slowed progression of Huntington’s disease.

Age-Related Cognitive Decline

We’ve all had a grandmother who called us by our sibling’s name, or a grandpa who forgot to unwrap

the Werther’s Original before popping it into his mouth – these are the innocent, simple, quaint,

seemingly unavoidable declines in cognition that accompany the aging process. Well, maybe they

aren’t unavoidable. Although most of the research focuses on neurological trauma and disease,

there’s evidence that intermittent fasting is good for basic age-related cognitive decline. I find it

interesting that this was “late-onset” intermittent fasting, meaning elderly rats who began fasting only

after showing signs of decline still wrought cognitive benefits. Contrast that with the stroke study in

which older rodents saw almost no benefit from fasting and a picture emerges: as long as they’re not

trying to counter a debilitating event, like ischemic stroke or trauma, older brains can also expect to

benefit from fasting.

Depression?

Depression has long been associated with lower BDNF levels as a prognostic of the disease, but it’s

only recently that researchers are entertaining the possibility that low BDNF and depression could be

causally related. And indeed – antidepressants actually increase BDNF signaling and synthesis in the

hippocampus (the part of the brain where depression “happens”). Could fasting help with depression

via upregulation of BDNF and promotion of neurogenesis? Perhaps. I’d say it’s worth a shot,

especially since skipping a few meals doesn’t require a prescription.

Obviously, since these are mostly rodent studies, and hard-and-fast peer-reviewed evidence of the

neuroprotective and neurogenerative effects of fasting in humans doesn’t exist yet, we’re only

speculating. But I’d argue they are plausible speculations worth pursuing. The mechanisms are there.

Speculations about IF’s other health effects – to general health and cancer and longevity and fat

loss – are being borne out by human research. Both the risk and barrier to entry are low. And it makes

sense in light of our evolutionary history as hunter-gatherers. In a recent interview, Mattson even

couches the neuroprotective effects of fasting in evolutionary terms, noting that during pre-agricultural

times of scarcity, people “whose brains responded best – who remembered where promising sources

could be found or recalled how to avoid predators — would have been the ones who got the food” and

lived to pass on their genes.

As I age, the risk of my uniquely human brain going screwy and sabotaging my selfish desires to

remain cognizant and engaged with life until the very end increases. It is not a foregone conclusion – I

know too many quick-witted, sharp-tongued folks thirty years my senior – but the chances do

increase. Since I don’t want that to happen, and the occasional fast is a nearly risk-free endeavorwith

proven benefits in other areas, I’ll continue to miss a few meals every now and then. It hasn’t hurt me

yet, it just might be one of the factors that allows me to live long and drop dead, and hey, since I’m fat-

adapted it’s not even a struggle to do it.

What say you, readers? Do the potential neuroprotective effects of fasting interest you? Why, or why

not?

Part Five – ExerciseIn previous installments, I’ve discussed the powerful effect of fasting on weight loss, particularly with

respect to adipose tissue. I’ve explained how intermittent bouts of going without food have been

shown to increase cancer survival and resistance and improve patient and tumor response to

chemotherapy, and I went over the considerable evidence suggesting that fasting can provide the life

extending benefits of caloric restriction without the pain of restricting your calories day in, day out. And

last week, I highlighted how fasting may have protective and therapeutic benefits to the brain.

As such you might be thinking that I only recommend fasting to the sedentary, the aged, and the

infirm. Surely I wouldn’t go so far as to recommend to the active, the athletic, and the jacked that they

engage in vigorous physical activity without having eaten a solid square meal beforehand – right? I

mean, no good can come of a fasted training session, as the gym bros with the sweet ‘ceps are so

quick to intone.

So, Sisson, what’s the deal? Can we exercise in the fasted state and live to tell the tale?

Yes. And there may even be benefits to doing it. There’s actually not a huge amount of literature on

the subject out there, with the bulk of it studying Muslim subjects during Ramadan and getting

mixed, sometimes negative results. I’m wary of using the negative results of the Ramadan training

studies to color our opinion of fasted training for the population at large for three major reasons: first,

Ramadan restricts daytime food and water intake during the fast. If you’re sedentary, you can

probably get by without guzzling water, but if you’re an athlete, or even just someone who dabbles in

a bit of lifting, some walking, and maybe a few sprints, your performance and results will suffer without

adequate hydration. And I’d say a complete and utter absence of water during daylight qualifies as

“inadequate hydration,” wouldn’t you?

Second, since eating and drinking are limited to pre-dawn and post-sunset hours, Ramadan often

means sleep deprivation. Studies show that sleep onset occurs later than normal, sleep duration is

lessened during the month (PDF), daytime sleepiness increases, and general performance of daytime

tasks decreases. We’re already aware of the importance of sleep for general health, but inadequate

sleep can also translate to poor athletic performance.

Third, the subjects in these studies most likely aren’t on a healthy Primal eating plan. Heck, they’re

probably not on a conventionally healthy whole foods diet. While it would be nice to believe that these

Ramadan fasters were feasting on fresh lamb, high quality extra virgin olive oil, extra-thick pastured

labneh, grass-fed breadless shawarma, and pomegranate salads, they were likely eating the same

junk that everyone in the industrialized world eats. And as such, they were probably poorly equipped

to shift smoothly and easily to the fat based metabolism required by fasting. Sure, they switched over

to burning their own body fat out of necessity and a sheer lack of calories, but it wasn’t the easy,

seamless transition that Primal eaters typically enjoy at the drop of a hat. For the carb-addicted,

fasting is mentally, physically, and spiritually taxing. For the fat-adapted, fasting often just happens.

As we often say around here, we eat WHEN – When Hunger Ensues Naturally. For folks with easy

access to the fat-burning switch, skipping a meal (or three) doesn’t ruin the day and preclude

exercise.

Right off the bat, then, I’ll say this: don’t even consider fasting and training if you’re not going to

hydrate, sleep, and become fat-adapted.

Now that we have those caveats out of the way, let’s look at some of the purported benefits of

exercising in a fasted state, as shown in the literature:

Improved Insulin Sensitivity

Intermittent fasting improves insulin sensitivity, as I mentioned before in the fasting and weight loss

post. A recent study found that this effect is heightened when combined with exercise (in this case

four days of endurance training each week). By the end of the study, subjects who fasted had lower

body weights (the only group not to gain weight), better body-wide glucose tolerance, and enhanced

insulin sensitivity. Furthermore, only fasted training significantly improved muscular adaptations to

training.

Improved Recovery from Endurance Exercise

Three weeks of overnight-fasted endurance cycling (with caloric restriction to boot) improved post-

workout recovery, maintained lean mass, lowered fat mass, and maintained performance. There was

unfortunately no control group, but this study does show that fasting doesn’t hurt (and it may help).

Another study suggested that fasted endurance training may quickly re-activate the muscle protein

translation that was negated in athletes who had eaten carbohydrates before training.

Improved Recovery from Weight Training

A 2009 study found that subjects who lifted weights in a fasted state enjoyed a greater

“intramyocellular anabolic response” to the post-workout meal. Levels of p70s6 kinase – a muscle

protein synthesis signaling mechanism that acts like an “indicator” of muscle growth – one hour after a

fasted workout doubled levels compared to one hour after a fed workout (in the same group). In other

words, fasting boosted (physiological indicators of) post-workout muscle growth.

For a further look, check out Martin Berkhan’s take on the study. Also note his recommendation that

10 grams of BCAA (branch chain amino acids) taken before the workout should boost the

enhancement without taking you “out of the fast.”

Improved Glycogen Repletion and Retention

What happens when you train in a low-glycogen state? If you’re used to running on full glycogen

stores, your performance might take a hit when you have to shift toward a more oxidative, fat-based

energy pathway. That’s understandable. Another thing that could happen is you learn to make do with

less glycogen by, well, making do with less glycogen. This is elementary stuff, folks. Just like your

muscles adapt to imposed stressors by getting stronger, your body adapts to low glycogen training by

learning how to train under low-glycogen conditions, thus sparing glycogen for when it’s really needed

and boosting performance when glycogen is actually available. It’s the classic “train low, race high”

idea that I’ve discussed before. It’s the specific adaptation to imposed demand (SAID) principle, only

in this case the “imposed demand” is a low-glycogen, low-food environment.

A recent study exemplifies this phenomenon, pitting a group of untrained, carb-fed cyclists against a

group of untrained, overnight-fasted cyclists and comparing both groups’ muscle glycogen content

and V02 max. Who won? The fasted group improved their V02 max by nearly 10% and their glycogen

content by over 54%, while the fed group improved V02 max by just 2.5% and glycogen by a paltry

2.9%. Lesson? Don’t eat 1.5 grams/kg body weight in cereal-based carbs pre-workout, and definitely

do not eat a delicious shake of waxy maize during your workout (unless you really really like cereal

and corn starch slurries).

What do you notice? Fasting does not instantly imbue its adherents with super powers. It’s not

supposed to. Improved performance during a given training session isn’t really the point of

fasted training. The point of fasted training, as I see it, is to maintain performance while enjoying the

metabolic benefits, like improved recovery, higher glycogen stores, better insulin sensitivity, and

improved muscle response to exercise. The point is that fasted training won’t kill you, won’t eat your

muscles, and it might even improve adaptation to exercise by forcing you to train in a “less

optimal” state, which can boost performance down the line. The Olympian isn’t going to be well-

served by doing the main event on an empty stomach, but he just might benefit from occasionally

training on one.

Mind and Matter Matter

The success of your training, whether it be lifting heavy things, running, sprinting, rowing, cycling, or

climbing, isn’t wholly dependent on your physical state. The amount of glycogen in your muscles and

liver, the mobility of your tissues, the structural size of your muscle cells, the distribution of the fiber

types within those muscle cells, the V02 max – these all matter and help decide the amount of weight

you’re going to put up, the time you’re going to hit, the miles you’ll be able to check off, and the

number of pullups you’ll complete, and fasting will obviously have an effect on these and other

markers. But just as important is your mindset, your personal approach to fasted training.

Me, I like a good long hike in the morning with maybe just a cup of coffee in me. It gives me exactly

the kind of steady energy I want without negatively impacting my performance (which doesn’t really

matter on a pleasant hike) or my enjoyment (which does). However, I don’t like playing Ultimate

Frisbee on an empty stomach. I can do it, but I feel like it impairs my performance – and when I play

Ultimate I play to have fun and win (as PrimalCon attendees are soon to find out). As far as lifting

goes, I’ll sometimes do it fasted, but I’m a big fan of fasting after a strength workout. I do so to milk the

post-workout growth hormone surge and because I’m just not that hungry immediately afterward. If

immediately stuffing one’s face was required for optimal gains after a workout, you’d think we’d all be

ravenous after lifting heavy things, but we’re not. I can do sprinting on an empty stomach, but I hit the

wall quicker (probably due to the depleted glycogen).

Don’t let the results of a study (or my words) dissuade you from doing something that seems to help

you. If fasted resistance training has you hitting PRs (or at least feeling like you could if you wanted),

keep doing it and disregard studies that suggest “THIS IS IMPOSSIBLE. YOUR GLYCOGEN-

DEPLETED MUSCLES WILL SURELY DISSOLVE INTO THE ETHER.” If fasted resistance training

has you lagging, eat something the next time and disregard studies that suggest “YOUR POST-

WORKOUT MUSCLE PROTEIN SYNTHESIS AND INSULIN SENSITIVITY WILL SKYROCKET TO

THE HEAVENS ABOVE.” In the long run, it may not matter. People have gotten in great shape eating

six meals a day or just one.

Whatever you do, don’t fall prey to paralysis by over-analysis, as did one of the Worker Bees. This

guy got way too deep in the fasting literature. He was reading PubMed articles, scouring online

weightlifting forums for anecdotes about fasted training and running multiple self experiments with his

eating and training. He become so enamored by the idea that working out in a fasted state would elicit

superior metabolic and performance effects that he found himself unable to workout if he’d eaten

anything at all. And it wasn’t a physical inability; it was a mental hang up. He became frozen, stuck

and often unable to reap all these wonderful benefits he spent so much time reading about, all

because he felt guilty working out if he’d had so much as a few pieces of beef jerky, a couple eggs,

and a banana. Don’t be that guy. He has since seen the light and now realizes that something is

better than nothing, that even “non-optimal” training can still be effective. But he wasted a lot of time

getting there because he obsessed over studies performed on people who were not him which

suggested some (often obscure) benefit to working out in a fasted state.

Do what works for you and if you find that fasted training qualifies, so be it. But don’t think it’s a

requisite of Primal living. While I absolutely recommend that people play around with it, and most

people find that Primal eating makes it easier, fasted training is not required.

Part Six – Choosing a MethodAssuming you’ve been keeping up with the series, you should be saying to yourself “Hey, maybe this

fasting thing would be a cool thing to try out, and it might even make me healthier/live longer/lean

out/lose weight/etc.,” which is a sufficiently extensive list of benefits, don’t you think? I could probably

go on theorizing and speculating about all the reasons why you should consider intermittent fasting,

but I’d rather move on to the implementation. Thinking about fasting, reading about fasting, and

reciting the benefits of fasting are all pointless if you don’t know how to go about doing it.

First, let’s go over the different variations of fasting. I’ll give a quick rundown. Each involves not eating

for a period of time, unsurprisingly.

A couple other rules that apply to all the given methods:

1. Sleeping hours (provided you don’t sleep-eat) count as fasting hours.2. Eat well regardless. While some fasting plans tout their adherents’ ability to eat crappy food and

still lose weight, I’m not interested in fasting solely as a weight loss method.

Okay, on to the variations.

Leangains

Martin Berkhan’s incredibly popular fasting protocol is slightly more involved than others, but still

pretty simple:

1. A daily 16 hour fast (Martin sometimes recommends 14 for women, who just seem to do better on shorter fasts) during which you eat nothing. Coffee, tea, and other non-caloric fluids are fine.

2. A daily 8 hour (or 10 for women) eating window.3. Three days of weight training, ideally performed at the tail end of the fasting period. To improve

performance and muscle protein synthesis, you have the option of consuming 10 grams of branched chain amino acids 10 minutes before the workout.

4. Always eat high protein.5. On training days, eat more carbs and less fat.

6. On rest days, eat more fat, fewer carbs, and slightly reduce calories.7. Most people begin their fast after dinner (say, 9 PM), workout in the afternoon (at around 12 PM),

and break their fast immediately post-workout (at around 1 PM), but you can use any schedule you prefer.

8. Your post-workout meal should have about 50% of your day’s caloric allotment (a real feast).

Who should try it?

Because it’s geared toward people interested in losing fat and putting on muscle and strength,

Leangains presupposes that you will also be lifting heavy things several times a week, usually in the

fasted state. Therefore, Leangains is best-suited for people who will be training on a regular basis. In

fact, it’s probably the most meticulously-designed IF program.

People with steady schedules will have more success than people with erratic schedules. A huge part

of Leangains is the hormonal entrainment induced by regular feeding times. Once you get locked into

your routine, your hunger hormones will adapt to the schedule, and the fasting should get easier, or

even effortless.

Eat Stop Eat

Put together by Brad Pilon, Eat Stop Eat is really basic:

1. Once or twice a week, don’t eat for 24 hours.2. Start your fast in the morning, at lunch, or at dinner. It doesn’t matter as long as you don’t eat for

24 hours.3. Break your fast with a “normal-sized meal.” Don’t try to make up for the lost calories by feasting.4. Exercise regularly.

Who should try it?

People interesting in fasting for the therapeutic benefits (cancer protection, autophagy, life extension,

etc.) would probably get a lot out of this method, as opposed to people interested in the body

composition benefits.

Going a full 24 hours without food is a much tougher slog than going for 16 hours. In my experience,

going lower-carb and higher-fat makes longer fasts easier, so I’d have to say a low-carb Primal eater

would do better than most.

The Warrior Diet

Ori Hofmekler’s plan is based on the feast-and-fast concept:

1. Eat one meal a day, at night, and make it a big one. A real feast. You have three or four hours to eat until full. So it’s basically 20/4 hours.

2. You can occasionally snack on low-calorie raw fruit and vegetables during the day, but try to limit protein as much as possible until the feast.

3. Exercise during the day, in a fasted state.

Who should try it?

People who have trouble sticking to a stricter fast will do better on the Warrior Diet, as it allows light

eating during the time leading up to the feast, but I wonder if you’d be squandering some of the

benefits by eating.

Alternate Day Fasting

Researchers often use this method in lab studies:

1. Eat normally one day (last meal at, say, 9 PM Monday).2. Don’t eat the next day.3. Resume eating the day after that (at, say, 9 AM Wednesday).4. It works out to a 36-ish hour fast, although there’s plenty of wiggle room. You could eat at 10 PM

Monday and break the fast at 6 AM Wednesday for a “mere” 32 hour fast.

Who should try it?

People who have no trouble going to bed hungry. With Leangains, Eat Stop Eat, and the Warrior Diet

methods, you can always manage to get to bed with a full belly; with ADF, you will be going to bed on

an empty stomach several times a week. That can be tough.

That said, the therapeutic benefits to serious conditions will most likely really be pronounced with this

way of fasting. The casual 20-something Primal eater who lifts heavy things and enjoys going out with

friends? Probably not ideal. The older Primal eater interested in generating some autophagy and

maybe staving off neurodegeneration? It might just work out. And while I’m not able to tell a cancer

patient undergoing chemotherapy what to do, I’d guess that the longer fasts will be more beneficial in

that regard, too.

But my personal favorite way of implementing fasting?

Eat WHEN – When Hunger Ensues Naturally

I’m not going to put any bullet points here, because none are required. Instead, I’ll give a few

scenarios:

I wake up bright and early on a Saturday morning. It’s about 65 degrees, the sun’s

out, Buddha’s walking around with the leash in his mouth, and Red Rock Canyon is kinda calling my

name. I’ve got my coffee already and I’m actually not all that hungry from dinner. You know what? I’ll

go on that hike, skip breakfast, and really work up an appetite for lunch. Or not. If I’m hungry

afterwards, I’ll eat. It’s a fast, but not really.

I hit the gym, put in a light workout, then swing by the beach for some sand sprints. I’m toast by the

end and have to stagger back to my car, but I’m not hungry. Even when I get home and smell the

grilled salmon, I have no desire for it. I might eat later that night, but only if my appetite returns.

I’m fasting post-workout only because it doesn’t occur to me to eat, not because I’m following a plan.

I’m away on business, stuck on a layover that’s turned into a delay that’s turned into an overnighter.

The only food available is a Kudos candy bar – I mean, healthy granola bar (they seriously still make

these?) from the mini fridge, a greasy pizza joint on the corner across the street from the hotel, a

Chinese takeout place next to the pizza joint, and a slew of fast food restaurants some ways down the

road. It’s late, I’m tired, I had a Big Ass Salad before I left for LAX… you know what? I’m just going to

skip the “meal.” I’ll figure out something at the airport in the morning (20 hour fast) or once I land (24

hour fast). And I’ll be okay either way.

That’s eating When Hunger Ensues Naturally.

This is the most natural, most effortless way of “fasting,” at least for me, because it allows a person to

eat intuitively. Although most people will eventually acclimate to more regimented fasting schedules,

and many may even need and thrive with that structure, I prefer a more fractal, loose, random pattern

of “missing” (in quotations because I don’t feel like I’m missing anything, and that’s the whole point!)

meals. I have no data on whether it’s as effective or more effective than the more popular methods,

but I do know that I’ll often fast for 16 hours and eat for eight, or skip an entire day of eating, or

sometimes (but very, very rarely) even approach a full 30 hours, and it seems likely that this random

pattern of eating characterized the eating “schedules” of our ancestors.

In short, we’re all doing the same thing, chasing the same goals. We’re all skipping meals, reducing

calories, staying active, and all the while we’re doing this without feeling miserable and restricted. It

just so happens that because we’re efficient Primal fat-burning beasts, switching over to burning our

own body fat reserves for energy during a fast is a natural, seamless transition. We often don’t even

notice it. There’s no effort involved.

That’s the key: lack of stress. If any or all of these fasting methods stress you out, make you irritable,

kill your performance, make you feel restricted, or reduce your ability to enjoy life, and these feelings

persist beyond the first five fasts you attempt (when some adaptation difficulties are totally expected),

you shouldn’t employ them. You should shelve fasting for a while and come back to it later, or never.

It’s not a “requirement” or anything. It’s just a tool you can wield if your situation warrants it. In fact,

this is the perfect opportunity to conduct an informal experiment of one. Try Leangains for a week or

two, then throw in a full 24 hour fast once or twice a week for a bit, then try the WHEN method.

Compare and contrast. How did you feel? How did you perform at work, at home, and in the gym?

Take some waist measurements perhaps, or analyze your favorite barometer of body composition to

see how the different fasting methods worked – or didn’t work – for you.

Part Seven – Q&A

By now, you should be caught up on all the benefits that fasting offers. By now, you’re likely either

intrigued by the practice, strongly considering taking it up, or basking in the smug satisfaction that

your longtime breakfast-skipping ways weren’t destroying your metabolism after all. But although I

tried to cover just about everything I could in the last six posts of this fasting series (links at the bottom

of this article), I apparently didn’t hit every angle, because I received a barrage of questions from

readers via email and comments looking for clarifications, answers, and explanations. I can’t quite

answer them all, but I did manage to put together a fairly representative selection of the most common

and relevant ones, and today I’ll provide answers.

I would like to IF but I have osteopenia and am concerned about losing bone mass. I have been gluten/dairy free for three years and paleolithic for about 3 months. Would IF be good for me?

Your hesitance is understandable, as caloric restriction has long been associated with bone loss,

likely due to the reduction in circulating IGF-1 (insulin like growth factor 1) levels. Since intermittent

fasting does not appear to have the same effect on IGF-1 levels, however, I’d imagine it’s pretty safe

for bone health. Just make sure you’re eating enough calories when you do eat (the IF rodents in the

study did not reduce calories overall) and lift some heavy stuff now and then, and I think you’ll be

good to go.

There was a study that found in utero IF had a negative effect on fetal skeletal development, but

you’re not typing this question from the womb, right? If so, amazing!

Won’t IF induce the body to break down muscle to get amino acids for de novo gluconeogenesis?

Let me hammer this point home: Once you become a fat-burning and keto-adapted beast, most of

your energy demands will be met by stored fat and ketones, so you won’t need to eat protein to spare

muscle. If you are fat-adapted and keto-adapted, fasting (at least IF) is protein sparing. If you DO

need to get some glucose for a hard workout, some will come from glycerol (from triglyceride) and

some from de novo gluconeogenesis. But you won’t need much from muscle tissue because your

glucose requirements have dropped, you are better at burning fats and ketones, and, presumably you

are NOT doing a 2-hour blood-letting in the gym.

As I often say, this is NOT the case when you are a sugar-burner. Then you probably DO need some

protein to stoke the gluconeogenesis process, and I’d suggest eating a protein-rich meal (see Meat)

before you embark on your fast so your body will have plenty of dietary amino acids on which to draw

for gluconeogenesis. Of course, this doesn’t apply to all you fat-burning readers out there. To you I

say, don’t worry about muscle loss during IF.

Workout intensity? Should I just be a slug during the fast, normal activity (long, slow walks or bike rides), intense workouts? Intense workouts usually make me hungry shortly after.

Long walks are great while fasting. My favorite pastime is an early morning hike on an empty

stomach. I typically fast for a couple hours after my resistance training to maximize growth hormone,

but then again, these days I’m generally doing bodyweight exercises (sometimes supplemented with a

weight vest). Most sources say to end your fast with a workout and eat afterwards. If intense workouts

make you hungry, save them for the end of the fast. That way you can derive the benefits of a long

fast, the benefits of a fasted workout, and the benefits of a massive feast after it all. Win win win.

Above all, I would stay as active as possible during the fast. Sitting around like a slug will only make

you dwell on food, and the lack thereof in your body. Don’t do that unless you want to obsess over

what you’re not eating. Walk, ride a bike, get some work done, do housework, read something. Just

keep mind and body active.

I am on a regimented meal/medication plan. I am adopting the Primal lifestyle, but I need to make room to allow for the tasting of these products. Sure, the menu items I can handle, as I just really need to take a couple bites, and that is it. The problem comes from having to taste for quality of the other items, like sauces that an employee makes, for consistency sake. In each, I might only have to taste a teaspoon or two at most to correct for seasoning, but when you have 10 items to test, that adds up.

How would you manage something like this? Would you make the working hours like a fast or something, to account for the tasting?

How does a chef fit the Primal Protocol?

Sounds like a great job to me! Personally, I wouldn’t worry a whole lot about fasting, especially as you

start a new job and acclimate to a new schedule. Plus you have a family, which can add even more

stress (love you, kids). Intermittent fasting might heap another stressor onto your busy schedule, so

keep that in mind.

If you’re dead set on it, though, there are two ways you can incorporate fasting into your schedule, as

I see it. First option: don’t sweat the tastings. You’re only doing a teaspoon at a time (and you could

probably cut that to half a teaspoon, am I right?), and since fasting is not controlled by an on/off

switch, you won’t necessarily be “breaking” the fast. Just consider your work day your fasting period.

You’ll be on your feet throughout the fast, so you’ll be staying active and your mind will be engaged

with things other than food. Er, scratch that: you’ll be engaged with food, but not necessarily eating it.

Another option is to fast on your off days. Assuming you get a day or two off, just do a full-on

legitimate fast for one of them. It doesn’t have to be a full 24 hours or anything, but try to make it at

least 16 or 18 hours without eating. Good luck!

Are you suggesting that it really is OK to skip breakfast?

Yes, I am. While epidemiology suggests that breakfast skippers are fatter and less healthy, that’s a

correlation, not necessarily causation. It could just as easily be explained by the fact that people are

more likely to skip breakfast because they’re overweight and want to lose weight. Or maybe because

skipping breakfast is widely regarded as an unhealthy activity (like eating red meat), those who are

already healthy are more likely to eat breakfast. See how it works? To date, there has never been

research conclusively showing that skipping breakfast causes the metabolism to “slow down” or the

skipper to gain more weight. In fact, the bulk of the evidence suggests that meal frequency and timing

have no effect on weight gain or health (and it might even be the opposite, as my fasting series

suggests).

What frequency do you recommend the average guy on Primal/paleo fast?

It depends entirely on the duration of your fasts. If you’re doing a Leangains-esque slightly

compressed eating window, daily fasts are in order and even well-tolerated. If you’re doing longer

fasts that stretch toward 24 hours and beyond, once a week is all you “need.” Two would be fine, as

well, but any more often might make it difficult to obtain enough calories to prevent the negative

effects we often see with chronic calorie restriction – muscle wasting, bone mineral density reduction,

libido lowering, general malaise.

Can I drink coffee or tea during a fast? How about adding cream or coconut oil to it – will that take me out of the fasted state?

Coffee is actually beneficial for fat-burning, especially during a fast. One study found that an infusion

of epinephrine – a hormone which coffee increases – during “starvation” enhanced its lipolytic and

thermogenic effects. In other words, fat-burning and metabolism up-regulated in response to

epinephrine (more so than usual). Epinephrine also lowers appetite, which can be extremely helpful

for people trying to stave off hunger during a fast. Tea, and anything non-caloric, is also fine.

Adding a pure fat source won’t “take you out” of the fasted state, and it may take the edge off the

hunger, but it will reduce the body fat you burn by a bit.

One should eat protein and carbs 30-60m post workout to build the muscles. Am I wrong?

If your sole intent is to get stronger, build muscle, and pack on weight – all fine, commendable goals –

then, yes, you should eat some protein and carbs within an hour of working out. Of course, this is

totally compatible with fasting. Just end your fast with a workout, and feast right after.

I play competitive sports 3d/week. Should one make sure to eat on the days one plays sports? Or is it more important to eat the day after?

Personally, I would eat on game days. It might be fun to try out a few fasted games, just to see how

you perform, but the likely optimal way to integrate fasting into competition is to save the fasting days

for your training days. By doing this, you’ll be “training low, playing high,” which should result in some

beneficial adaptations after training and improved performance in the game (when you’re “high,” or

fully replete with nutrients and calories).

Should fasting be considered when you try to GAIN weight?

Usually, no. But there are a couple special cases where fasting might help someone gain mass.

I’ve mentioned Leangains a number of times in the past several posts, and I’ll do it again. It’s right

there in the name: “lean” and “gains.” Plenty of people have success gaining lean mass on the 16/8

Leangains IF plan. It’s slower gaining, but it minimizes and sometimes even eradicates fat gain. Of

course, you also have to be sure to lift heavy weights and overfeed on training days (most find the two

are a natural pairing, though).

I’ve also heard from people who used intermittent fasting to increase their appetite to the point where

eating enough calories to gain weight was possible. The constant snacking was keeping them

perpetually full, whereas a good solid 18-20 hour fast really ramped up their hunger and allowed them

to eat an actual meal.

Can I take vitamins or supplements during a fast?

Sure, but absorption might be hampered without a meal to go along with it. Vitamin and mineral

absorption is generally better in the presence of food, particularly fat. For instance, vitamin K2 is

absorbed seven times greater when taken with a meal than without (PDF). I personally skip the

supplements when I fast.

I’m actually posting this in a fasted state. It’s been about 20 hours since my last meal. Should I keep fasting till I hit the 48 hour mark? I’m not really hungry, but I’ve been doing the one meal a day thing for some time. Thoughts?

Sure, give it a shot. I always say that pushing the limits is healthy from time to time. Plus, this will give

you a good baseline. If you know you can fast for, say, 36 hours without doing too much damage or

incurring too much stress, you’ll know your limits for the future. People have fasted for far longer and

lived to tell the tale, and you seem to be reasonably experienced. Good luck.

Should pregnant or breastfeeding mothers do it?

Probably not. Whatever you do, listen to your hunger signaling. Don’t force yourself to adhere to an

arbitrary fasting regimen just because it’s shown to confer all sorts of benefits in other, non-pregnant

populations. While I wasn’t able to find any studies on breastfeeding and fasting, there are several on

maternal fasting:

Intermittent maternal fasting alters fetal breathing patterns. Intermittent maternal fasting alters fetal heart beat. Maternal “diet restriction” increases gestational diabetes and induction of labor.

There have been studies on calorie restriction and lactation, and it looks like mild calorie restriction

(coupled with exercise) has little impact on breastfeeding. If you’re going to do this, make sure your

milk quality and quantity aren’t negatively affected. Keep the fasts short (12-ish hours) and infrequent,

just to be safe. And, of course, consult your doctor prior to doing it.

Should I fast if I’m trying to get pregnant?

Generally, no. Fasting is a stressor, and if you’re already stressed out over something and cortisol is

high (say, because you’re trying to get pregnant and finding it difficult), throwing a fast on top of that

will likely compound the problem and make it harder to get pregnant. Cortisol is a potent inhibitor of

fertility.

However, if you find that fasting improves your health, reduces your weight, enhances your

metabolism, fixes your metabolic syndrome, which can all have negative effects on fertility, it will likely

have a net benefit. If you intend on fasting, opt for the “WHEN” method rather than a regimented one,

and keep your fasts pretty short. Fertility requires “plenty.” An extended fast does not exactly send

that message to your body. A 12 hour fast every once in awhile should probably be the limit, and only

if it’s improving other subjective and objective markers of health.

On the other hand, men who are trying to impregnate someone may find it helpful to fast.

Should kids do it?

Kids shouldn’t be put on a fasting regimen or anything like that, but they might forget to eat now and

again, and that’s totally fine. As a kid, I often spent my summer days in a fasted state from early

morning through early evening, simply because I was out running around, playing capture the flag,

skipping rocks, and generally getting into trouble. It didn’t always occur to me to eat. I think I turned

out okay.

Should seniors do it?

Seniors should absolutely try it. Although we’re talking elderly humans here, elderly rats derive a lot of

beneficial neurological effects from intermittent fasting. I see no reason why older folks can’t also

enjoy the neurological, life-extending, and health-promoting benefits of fasting, too. It might increase

healthspan, stave off age-related cognitive decline, and improve quality of life.

Under what circumstances would you recommend that someone not fast?

High stress. Overtraining. Chronic lack of sleep. SAD dieting. And then there’s my previous take on

the subject.

I’m thinking about giving IF a try and am wondering if you have any thoughts on how to track its effectiveness. Would you recommend a logbook? What should I be recording and looking for?

I think for many people looking to track the effectiveness of a given fasting protocol, a logbook can be

extremely helpful. Think of it like a training log for your workouts. You can track:

Objective measures, like weight, body fat percentage, waistline, blood sugar, dress size, hours slept, plus markers of physical performance, like weight lifted, reps completed, distance run/walked/cycled/rowed. These are easy to track, as they come with numerical figures built-in.

Subjective measures, like mood, energy levels upon waking, energy levels halfway through the fast, energy levels during workouts, perceived performance during cognitive tasks. These are trickier to track, so you may want to assign numerical figures to them in order to quantify what is essentially a

subjective measurement. Something as simple as rating your mood 1-10, with 1 being “very bad” and 10 being “very good,” should suffice.

And if you’re fasting for a specific health effect, say to boost the effectiveness of chemotherapy, you’ll

definitely want to track those specific health markers.

Ultimately, what I hope this series has done is inspire you to self-experiment with fasting. I always

maintain that fasting is not essential to Primal living, but it certainly seems to mesh well with it.

Whatever you do or don’t do, I want to stress something: don’t stress out over this stuff. If you’re going

to give it a shot, do so and do so intelligently – by tracking your progress, maybe even doing so

formally – but don’t drive yourself crazy obsessing over the minutiae. Whatever you do, good luck!