Resistant Starch: A Low-Carb Carb?

Resistant Starch:A Low-Carb Carb

Allison BaileyFall 2016http://www.webweaver.nu/clipart/img/misc/food/chinese-take-out-container.png

Hello, everyone, and welcome to my presentation on Resistant Starch. You may be wondering about my title: resistant starch a low-carb carb? Now obviously resistant starch is technically a carbohydrate and therefore not really low-carb, but resistant starch gets its name from its characteristic of being impossible or difficult for human digestive enzymes to break down. Functionally, then, a person ingesting resistant starch will have different metabolic effects than a person intaking a more easily digestible carbohydrate. Youll see what I mean as we continue.1

http://time.com/4318201/carbohydrates-weight-loss-resistant-starch/Published online May 6, 2016

Claims that even though health-conscious Americans avoid carbs, they can and should be eating resistant starches

Listed benefits include weight control, unspecified changes to body composition, increased satiety, and serves as a prebiotichttps://upload.wikimedia.org/wikipedia/commons/thumb/b/b3/Time_Magazine_logo.svg/3000px-Time_Magazine_logo.svg.png

Earlier this year, Time Magazine published an online article entitled, Eat This Carb and You Wont Gain Weight! Wow- what amazing click-bait! If you access the link I provided, not only can you read this article, you can also see the umpteen ads that Time is making a fortune from when desperate to lose weight people click on this article hoping for a miracle weight loss solution. Suddenly Im seeing unripe bananas and bizarrely textured leftover rice in a new light!

The article claims that even though health conscious Americans apparently all avoid carbs, resistant starch is a key way to help control weight. The Time article cites two research studies, which I will discuss in the presentation, and broadly discusses many health benefits from resistant starch, such as weight control, possible changes to body composition, and fermentation in the large intestine as a prebiotic.2

Four Main Types of Resistant Starch

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However, the Time article neglects to mention that there are actually four major types of resistant starch. The first type, simply called RS1, consists of indigestible starch within plant cell walls from some whole grains and seeds. Remember, cell walls are made of cellulose, so in this case, the starch is indigestible because amylase is physically blocked from the starch. The second type, RS2, requires ripening or cooking for the amylose to be released from the granules in which it is very tightly packed. While the glysosidic bonds connecting the monomers are alpa 1-4, the tight packing prevents amylase from accessing the bonds to break them down during digestion. RS1 and RS2 are considered dietary fibers, because they naturally cannot be broken down by human enzymes. However, RS3 and RS4 are considered functional fibers, because human food processing causes resistant starch to form. RS3, or retrograde starch, is formed when starchy foods such as rice and pasta are cooked then cooled as the structure changes, making it hard for enzymes to bind. A more crystalline structure with double helices makes RS3 more resistant to hydrolysis by digestive enzymes. RS4 is chemically modified starch produced in food laboratories as a functional source of fiber, purposefully mimicking the chemical properties that make the other forms naturally resistant to digestion. While the article alludes to all of these types, the research studies it refers to use RS2 and RS4, respectively, so this presentation will focus on those as well.3

Resistant Starch and Type 2 DiabetesGargari et al., 2015 in Complementary Therapies in MedicineIs there any place for resistant starch, as alimentary prebiotic, for patients with type 2 diabetes?

Now lets look at the first study cited by the article, which uses resistant starch 2. The aim of this study is to investigate whether RS2 can be used to decrease inflammation and improve metabolic markers such as glucose tolerance and blood lipid profile in women with type 2 diabetes. The hypothesis hinges on the fact that RS2, remember, the kind found in green bananas, is fermented in the large intestine by the gut microbiota. As a prebiotic, RS2 is thought to increase anti inflammatory bacteria such as lactobacilli and Bifidobacteriaceae as well as produce short chain fatty acids such as butyrate which also have anti inflammatory properties. 4

Baseline measurements 60 middle-aged women with T2DMTriple-blinded, randomized controlled clinical trial

10 g/d of maltodextrin (placebo)

10 g/d of high amylose maize starch (RS2)8 weeksPost-measurements

Measurements:

Fasting blood sugarHbA1cTriglyceridesCholesterolhsCRPIL-6TNF

So heres the experimental design of this study, which was a triple-blinded, randomized controlled clinical trial. After baseline measurements were taken, 60 women with type 2 diabetes were divided into either a treatment group or control group. The treatment group took a total of 10 g/d of Resistant starch as high amylose maize starch suspended in water. The control group also took 10 g/d but of maltodextrin. After 8 weeks, the trial ended and final measurements were taken. The data collected included measurements of glycemic control including fasting blood sugar and glycated hemoglobin, lipid profile including triglycerides and cholesterol, and the inflammatory markers high sensitivity c reactive protein, IL 6,and TNF alpha.5

RS2 and Diabetes ResultsImproved:

HbA1c TriglyceridesHDLTNF

No change:

Fasting blood sugarhsCRPIL-6

Supplementation with RS2 improves blood sugar control, decreases inflammation, and improves lipid metabolism

What this study found was that glycated hemoglobin, serum triglycerides, and TNF alpha significantly decreased while HDL increased. They found no signficant changes in fasting blood sugar, high sensitivity CRP, or IL 6. Their conclusion was that supplementation with RS2 improves blood sugar control, decreases inflammation, and improves lipid metabolism in women with type 2 diabetes. 6

Limitations and Weaknesses

Mixed resultsDid not measure SCFANo gut microbiotal measures despite that being a main part of their hypothesis

However, it is curious that HBA1C improved but not fasting glucose, and only one of the measured inflammatory markers decreased. I think their conclusion is a bit overenthusiastic about the health effects of RS2. Particularly when you consider a few major things they did not measure, including serum levels of short chain fatty acids and importantly, the gut microbiota. The results of this study are promising but limited, especially since their title focuses on RS2 as a prebiotic. I imagine it would have been very expensive to collect fecal samples from a sample of 60 women, but it would have potentially added to their papers impact.7

Resistant Starch and Protein IntakeGentile et al., 2015 in Nutrition JournalResistant starch and protein intake enhances fat oxidation and feelings of fullness in lean and overweight/obese women

The second study cited by the Time Magazine article looked at RS4, the chemically modified starch that works as a functional fiber. Also published in 2015, this study again looked at middle aged women, however, the women had different body compositions ranging from lean to obese and were otherwise healthy. This study aimed to looked at the possibility of combining RS4 and protein to change energy expenditure and increase satiety as a way to promote weight management. They chose to look at RS4 because of some recent studies indicating that it may have underappreciated weight loss potential. In particular, a study done on mice by Keenan et al in 2015 found that RS4 was more effective for weight loss than RS2. Their working hypothesis was that due to proteins established satiety promoting effects and RS4s potential, the combination of the two would encourage fat oxidation while increasing satiety more than either protein or resistant starch alone. 8

24 middle-aged womenSingle-blinded, randomized crossover design

Waxy maize starch (control)1 of 4 pancake meals

Measurements:

RMR, RQ, TEMInsulin, glucoseGLP-1, PYYGhrelin, leptinVAS scalesHungerDesire to eatSatietyWaxy maize starch + whey protein

RS + whey proteinRSFigure 1 from Gentile et al 2015

This experiment was conducted as a single blinded randomized crossover design with 24 women who were brought into the lab after a 12 hour fast to consume 1 of 4 pancake test meals made from either control starch, control starch plus protein, resistant starch alone, or resistant starch plus protein. Other than that is was type 4, no other information about the chemistry of the resistant starch was given. You can see the time line of the test day in the figure as some basic baseline measurements were taken, RMR was measured, an initial blood draw and set of Visual Analog Scales (or VAS) were completed. The VAS were participant subjective measures of hunger, desire to eat, amount that could be eaten, and satiety. After the test meal was consumed, participants were retained to measure the thermic effect of the meal through indirect calorimetry and VAS and blood draws were completed hourly for 3 hours. A final body composition measurement was obtained. The blood was used to quantify a large number of measurements, which I have summarized here, including insulin and glucose, satiety factors GLP-1 and PYY, as well as ghrelin and leptin.9

RS4 and Protein Major Findings

RS + protein resulted in increased fat oxidation

Both protein meals led to increased fullness

No change in circ. hunger/satiety factors

Meals combining RS4 and protein lead to increased fat oxidation, PYY, and satiety.

Figure 4 from Gentile et al 2015

Despite the rather broad measurements taken, the major findings can be summarized quite simply. First, the Resistant Starch and protein pancakes led to decreased carbohydrate oxidation compared to the other meals, as seen in panel a of figure 4. This meal also led to significantly increased fat oxidation compared to other meals as seen in panels b and c. As expected, both protein meals led to increased feelings of fullness and decreased feelings of hunger as measured by the visual analog scales, but there was no change in circulating hunger or satiety factors. The Resistant starch had no effect on fullness or satiety. However, at the 3 hour post prandial mark, peptide YY was increased significantly in the Resistant starch and protein meal compared to just the resistant starch and just the control starch. The paper concluded that meals combining RS4 and protein lead to increased fat oxidation, PYY, and satiety which may help with weight loss efforts. 10

Limitations and Weaknesses

Only 9 out of 24 women did the control starch + whey protein test mealCould not measure plasma variables for that mealMore research is needed about what role the RS4 played versus the proteinLacking comparison of RS2 vs RS4I have not failed. I've just found 10,000 ways that won't work. Thomas Edison

This study is not without some major limitations and weaknesses. To start, the paper is clear that only 9 out of the 24 women completed the control starch and whey protein test meal and they were not able to analyze plasma variables for that meal, which is a problem because this was an important control for the effects of protein. We know that protein promotes satiety and has a lower RQ than carbohydrates, so it is unclear what role the RS4 actually played. Given that part of their rationale for using RS4 was that it may be more effective for weight loss than RS2, it would have been nice to see a comparison between RS2 and RS4. RS2 is naturally found in foods while RS4 is a potentially marketable functional food. It seems like both of these papers felt compelled to spin rather mixed results as positive in order to get published, which is a shame because resistant starch seems like it does have potential to aid in weight control or weight loss and gut microbiota are such a hot area of research. The pressure to spin the results makes it difficult for the reader to determine what is really going on. I always think about how Thomas Edison would be ashamed that we do not value results that do not support our hypotheses.11

Problems with Article

Lumps carbs into refined sugar or resistant starch

Does not distinguish between types of RS

Slips in lack of evidence for actual weight loss

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Now that we have examined the studies the Time Magazine article is based on, lets revisit it for a more critical look. My first problem with the article is that it lumps all carbohydrates into either two categories: blood-sugar spiking refined sugar or miracle fermentable resistant starch. The article does not discuss complex carbohydrates or fiber other than resistant starch, while these carbohydrates certainly have different metabolic effects than refined sugar. This needlessly promotes the negative hype around carbs leading to reader bias and misinformation. This article also, as previously mentioned, does not distinguish between types of resistant starch, even though they have different chemical properties and may have different metabolic functions, particularly as regards fermentability. The article also alludes to great weight management claims but at the end slips in that there is no evidence yet for actual weight loss, just weight maintenance. For me at least, weight maintenance isnt really the issue, I need to lose a few pounds and if I had no nutrition knowledge would be eagerly looking for a way to do so.12

Questions Remaining

How does type of RS impact its potential for weight control?

Can RS lead to actual weight loss or just weight management?

Is RS more effective than just eating the recommended amounts of dietary fiber from typical sources?

https://image.freepik.com/free-icon/question-mark_318-52837.jpg

With those article problems, we can now ask some questions that need further invesitgation. First, How does the type of resistant starch impact its potential for weight control? Are some types, such as RS4, indeed more efffective than other types? What about RS3, which is probably the most commonly consumed because it is found in leftovers even after reheating? Also, can resistant starch lead to actual weight loss or just weight management? A longer term clinical trial would be needed here with the rest of the diet and physical activity controlled. And finally, is focusing on resistant starch more effective than just eating the recommended amounts of dietary sources form typical sources such as whole grain bread, fruit, and vegetables or are they just trying to find ways to market a new cash product? A randomized crossover design could be used to test this, with participants alternately eating a diet where fiber needs are met through Resistant starch or intestinally fermentable fruits and vegetables.13

References

Gargari BP, Namazi N, Khalili M, Sarmadi B, Jafarabadi MA, Dehghan P. Is there any place for resistant starch, as alimentary prebiotic, for patients with type 2 diabetes?Complementary Therapies in Medicine. 2015;23(6):810-815. doi:10.1016/j.ctim.2015.09.005.

Gentile CL, Ward E, Holst JJ, et al. Resistant starch and protein intake enhances fat oxidation and feelings of fullness in lean and overweight/obese women.Nutrition Journal. 2015;14(1). doi:10.1186/s12937-015-0104-2.

Gropper SAS, Smith JL.Advanced Nutrition and Human Metabolism. 6th ed. Australia: Wadsworth/Cengage Learning; 2013.

Higgins JA. Resistant Starch and Energy Balance: Impact on Weight Loss and Maintenance.Critical Reviews in Food Science and Nutrition. 2014;54(9):1158-1166. doi:10.1080/10408398.2011.629352.

Keenan MJ, Zhou J, Hegsted M, et al. Role of Resistant Starch in Improving Gut Health, Adiposity, and Insulin Resistance.Advances in Nutrition: An International Review Journal. 2015;6(2):198-205. doi:10.3945/an.114.007419.

Wang S, Li C, Copeland L, Niu Q, Wang S. Starch Retrogradation: A Comprehensive Review.Comprehensive Reviews in Food Science and Food Safety. 2015;14(5):568-585. doi:10.1111/1541-4337.12143.

To conclude, here are my references and thank you for viewing my presentation. I would be happy to answer any questions or hear any feedback you may have via email.14