Fats as ergogens

Fat bad, Carbohydrate good Traditionally fat as an ingested fuel source during exercise has been considered taboo Conversely, the ability to oxidize fat preferentially during exercise has been the holy grail Carbs thought of as the preferred macronutrient ingested prior to or during exercise

Generally, high dietary fat intake is associated with high incidence of heart disease and other maladies Fat also has more energy per unit mass (9 cal/gram) – Contributes to caloric surplus and fat gain

Why is fat oxidation over glycogen the holy grail Typical energy stores in the form of glycogen for a well fed athlete – 2500 cal Typical energy stores in the form of triglycerides for a well fed athlete – >100,000 cal

Fat good Fats essential for many biological processes – Membrane phospholipids – Steroids – Transport of lipid soluble vitamins

Types of Lipids Triglycerides – Glycerol and fatty acid – Storage form of fat in humans Free fatty acid – Ingested fats released into blood – Triglycerides broken down and released into blood Phospholipids – Structural Steroids – Regulatory

Types of fatty acids Saturated – Bad fats Monounsaturated – Olive oil Polyunsaturated (PUFA) – Essential fatty acids – Must be ingested in diet Omega 3 and omega 6, linoleic acid, alpha linoleic acid, arachidonic acid

Dietary recommendations < 30% of the diet should come from fat in sedentary individuals Athletes may need greater caloric intake, but fat intake should not increase in absolute terms – ~20-25 % calories from fat Many athletes may restrict fat intake to below 15% – Impairs regulatory functions, vitamin transport, membrane integrity

Types of fat in the diet Although sedentary or active individuals may consume less than 30% of calories from fat, high proportion typically from saturated fats – Keep saturated fat intake less than 10% of caloric intake – PUFAs should constitute 20% (equal amounts of omega 3 and omega 6) Tough to do without supplements

Fat/lipid metabolism during exercise

The Substrate Utilization Paradox As exercise intensity increases, the relative contribution from fat oxidation decreases During light to moderate exercise though, the increase in oxygen consumption offsets the relative decrease in contribution from fat – Up to ~60 – 70 % – No lactate accumulation

Muscle fuel sources in highly trained endurance athletes

Also, as duration of exercise progresses, relative contribution from fat metabolism increases – Decrease in RER after several hours of light intensity exercise – Determined by substrate availability and oxidative capacity

Contributions of four energy sources over prolonged time in endurance athletes

Fat loading Vukovich et al (1993) Randall cycle – Glucose fatty acid cycle?? – At rest active in heart, diaphragm and skeletal muscle

Prior studies In support – In rats elevated FFA and heparin decreased carbohydrate utilization and spared glycogen – Confirmed in humans Against – TG (MCT and LG) feeding to rats did not spare glycogen – Hargreaves saw no effect in one-legged knee extensions (intralipid)

Purpose Compare saturated (Costill) vs unsaturated (hargreaves) to see if differential effect Exercise for 60 min at 70 % VO2max

Results?

What did they decide? Fat loading decreased glycogen utilization in both intralipid and fat feeding trials Greater elevation in FFA levels with FF did not result in greater glycogen sparing compared to intralipid

Fat adaptation Burke et al (2001) Fat adaptation may be advantageous over fat loading for prolonged exercise

Prior studies Same lab reported 5-day adaptation to high fat/low carb diet resulted in increased fat oxidation and reduced glycogen oxidation during 2 hr cycling at 70 % VO2peak – 2 fold increase in fat oxidation vs control – No clear advantage during 30 min TT following 2 hr bout

Blood glucose availability during the TT may play a role in performance If maintain or elevate blood glucose during bout, does increased fat oxidation persist? – If so, does this result in improved performance?

Purpose Determine if enhanced fat oxidation with 5 day high fat diet persist with high CHO availability – Ho: High CHO intake would eliminate increased fat oxidation

Results

What did they decide? 5-day adaptation to high fat diet enhanced fat oxidation during exercise despite increased CHO availability CHO/glycogen sparing still enhanced to levels observed in low CHO availability These adaptations still did not enhance performance in the TT at the end of the 2 hr bout

Fat adaptation and ultraendurance Carey et al (2001) More on the fat adaptation diet and increased CHO availability

Prior studies Same lab showed previously that 5-day adaptation to high fat diet and increased CHO availability before and during 2 hr bout, increased fat oxidation and decreased CHO oxidation, but did not improve performance in subsequent 30 min TT

Maybe the bout was not sufficient intensity or duration to deplete glycogen stores If this is the case, increased fat oxidation may not be of benefit until glycogen is depleted

Purpose Determine if fat adaptation and increased CHO availability spare CHO during 4 hr cycling bout > 65% VO2peak and improves performance in subsequent 1 h TT

Results

What did they decide? Fat adaptation did result in significant sparing of CHO during the 4 hr bout Performance in subsequent TT was not enhanced (p=0.11)

Intramuscular TG Utilization Intramuscular triglyceride oxidation is dependent upon exercise intensity and duration In animals, whole body exercise to exhaustion results in decreases in intramuscular TG content Lower intensity exercise, results are equivocal

Intramuscular TG utilization is also fiber type dependent – FOG>SO>FG

In humans using various modes of exercise, TG content of VL decreased % Exercise prolonged at % VO2max During intense exercise 5 min in duration, TG decreased 29 % Significant contribution of oxidative metabolism at 5 min