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Fats as ergogensFats as ergogens
Fat bad, Carbohydrate goodFat 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 Why is fat oxidation over glycogen the holy grailglycogen 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 goodFat good
Fats essential for many biological processes– Membrane phospholipids– Steroids– Transport of lipid soluble vitamins
Types of LipidsTypes 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 acidsTypes 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
http://www.kumc.edu/research/medicine/biochemistry/bioc800/lip01fra.htm
Dietary recommendationsDietary 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 dietTypes 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 Fat/lipid metabolism during exerciseexercise
The Substrate Utilization The Substrate Utilization ParadoxParadox
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 Muscle fuel sources in highly trained endurance athletesendurance 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 Contributions of four energy sources over prolonged time in endurance over prolonged time in endurance
athletesathletes
Fat loadingFat loading
Vukovich et al (1993) Randall cycle
– Glucose fatty acid cycle??– At rest active in heart, diaphragm and skeletal
muscle
Prior studiesPrior 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)
PurposePurpose
Compare saturated (Costill) vs unsaturated (hargreaves) to see if differential effect
Exercise for 60 min at 70 % VO2max
Results?Results?
What did they decide?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 adaptationFat adaptation
Burke et al (2001)Fat adaptation may be advantageous over
fat loading for prolonged exercise
Prior studiesPrior 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?
PurposePurpose
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
ResultsResults
What did they decide?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 Fat adaptation and ultraenduranceultraendurance
Carey et al (2001)More on the fat adaptation diet and
increased CHO availability
Prior studiesPrior 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
PurposePurpose
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
ResultsResults
What did they decide?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)
http://www.kumc.edu/research/medicine/biochemistry/bioc800/lip01fra.htm
Intramuscular TG UtilizationIntramuscular 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 25-50 %• Exercise prolonged at 55-70 % VO2max
• During intense exercise 5 min in duration, TG decreased 29 %• Significant contribution of oxidative
metabolism at 5 min