Fats

Functions of Fat

• Fuel for cells• Organ padding and protection• transport fat-soluble vitamins• Constituents of cell membranes• Constituents of hormones

Categorization of Fats

• Degree of Saturation– Saturated– Monounsaturated– Polyunsatrated

• Chain Length– Short– Medium– Long

Saturated Fat

• Lacks C-C double bonds• Saturated with H• Animal fat & tropical

oils• Most unhealthy??• Hydrogenated oils

Monounsaturated Fat

• Contains single C-C double bond

• Most healthy• Most common

– Olive oil– Canola oil– Peanut(s) oil– Walnuts– Almonds

Polyunsaturated Fat

• Two or more C-C double bond

• Omega 3– Flax oil, Fish oil– -linolenic acid

• Omega 6– Corn, soyben, safflower,

sunflower– Linoleic acid

Hydrogenated Fats

• Process used to convert unsaturated oils into saturated oils– Increases temp at which oil burns– Increases shelf life– Stays in mixture better

• Health impact is same as saturated fats

Trans Fatty Acids

• Formed from hydrogenation process• May have worst health impact of all fats

TABLE 5.1 Fatty Acids in fats and oilsOil/Fat Saturated Mono-unsat PolyunsatBeef 50 43 4Chicken 30 46 22Tuna 27 26 37Olive 14 74 9Canola 6 62 30Tuna 27 26 37Coconut 87 6 2

Fatty Acids by Chain Lengths

• Short Chains– 6 or less carbon atoms– Found in butter, coconut oil, palm kernel oil

• Medium Chain– 8 or 10 carbons– Absorbed into blood more quickly

• Long Chain – 12 or more carbons, most are 16 and 18– Most common in the diet

Key Terms

• Lipolysis• Triglycerides (triacylglycerols)• Glycerol• Gluconeogenesis

– Lactate– Glycerol– Alanine

• 3500 kcal = 1 lb fat

Sources of Triglycerides/Fatty Acids for Fuel

• Adipose tissue– 140 lb @ 3% fat = 20,000 kcal– 280 lbs @15% fat = 170,000 kcal

• Muscle Triglycerides– 2,000 - 3,000 kcal– Supplies energy at 1/3 rate of CHO

• Plasma triglycerides– Minimal contribution (40 kcals)

Characteristics of Fat That Make It Preferential to CHO as a Fuel Substrate

Reserve

• 2+ X as much energy per gram• Not hydrated when stored

– 3 g H2O per g glycogen– Equivalent energy as glycogen would increase

body weight by 50% or more

FFA Availability

• At rest, 70% of all FFA released during lipolysis are re-esterified.

• During exercise, re-esterification is suppressed by 50% which increases FFA avaiability.

• Exercise increases lipolysis (300%) which contributes to the plasma FFA.

• Blood flow to adipose tissue and to muscle is increased increasing overall delivery of FFA

FFA Transport into Muscle

• Protein carrier mediated process• Carriers become saturated at high plasma FFA

levels (1.5 mmol/liter)• Muscle contraction increases the activity of

the carriers which increases the transport of FFA into the cell.

Intramuscular Triglycerides (IMTG)

• Type I muscle fibers have higher concentrations.

• Endurance training translocates the IMTG next to the mitochondria

• Lipolysis of IMTG mediated by hormone sensitive lipase (HSL) and inhibited by insulin, just like in adipose tissue.

Training

Fig. 2. Contribution of the four major fuel substrates to energy after 30 min of exercise at 25%, 65%, and 85% of VO2max in fasted subjects.

Fig. 4. Substances providing energy during exercise at a given absolute intensity of 65% VO2max before and after 12 weeks of training.

Fat Oxidation and Exercise Duration

• Fat oxidation increases as duration increases• Maximal oxidation rates are approximately 1.5

g/min.• Fat oxidation increases probably because

glycogen goes down.

Fat Oxidation and Intensity

• Fat oxidation rates peak at ~ 60-65% VO2max in trained (VO2max = 60 ml/kg/min) and then declines (range 50-85%)

• Fat oxidation rates range from 0.23 g/min to 0.91 g/min)

• At low intensities (25% VO2max), most fat is from adipose tissue

• At 65% VO2max, most is from IMTGs• At high intensities, fat oxidation is suppressed

Why is Fat Oxidation Suppressed at Higher Exercise Intensities?

• Reduced blood flow to adipose tissue due to sympathetic constriction of vessels

• Lactate increases re-esterification of Fas• Transport into the muscle is reduced• Breakdown of IMTG is reduced• Transport into mitochondria is reduced

Muscle Adaptations Which Enhance Fat Use

• Increase in enzymes of beta-oxidation• Increase of ETS capacity• Increase sensitivity of SNS stimulation• Increase in transport mechanism across

sarcolemma and within muscle

Systemic Adaptations Which Enhance Fat Use

• Decrease in insulin• Decrease in lactate• Increase delivery of substrate

– Cardiovascular– Capillarization

Fat Supplementation During Exercise

• Cannot consume FFA because they are too acidic and require protein carrier for absorption

• LCT are slowly absorbed and rate of uptake by muscle is slow

• MCT are directly absorbed and easily transported into muscle– 30 g is limit of tolerance– Practically can contribute no more than 10% of

total energy

Short-Term Dietary Fat Supplementation Before Exercise

• Consuming high fat diet increases fat utilization but reduces or does not change exercise intensity that can be tolerated

• Consuming high GI CHO just prior to exercise will inhibit fat utilization during first 50 min of exercise and increase use of blood glucose

Long-Term High-Fat Diet and Exercise Tolerance

• Exercise duration may be increased at intensities <65% VO2max

• Durations at competitive intensities are not improved

Combined Fat and CHO Loading

• No demonstrated beneficial effect on performance of combining high fat diet in days before exercise and CHO loading immediately before exercise.

Fat Intake During Recovery

• Requires 2gm/kg to resynthesize IMTG• Take ~ 22 hrs to resysnthesize• Optimizing IMTG may compromise CHO