Lipids
To promote good health, lipid intake should probably not exceed 30% of the diet’s energy content. Western diet – 35%
100-150 g/d
Of this, at least 70% should come from unsaturated fatty acids.
Lipids
Long chain FA (LCFA)• C14-C22
Medium chain FA (MCFA)• C8-C10
Short chain FA (SCFA)• 6C or less
Lipids
Digestion • Gastric lipase
• Converts TG to FA, diacylglycerols
• Pancreatic lipase• Somewhat specific to LCFA (>10C)
Lipids
Triglyceride hydrolysis• 3 FFA• acylglycerol
Slightly water soluble Incorporate into
micelles• Transport vehicles
Lipids
MCFA• Absorbed into portal blood – liver
LCFA• Bypass liver• Released in form of chylomicrons
(lipoproteins)• To circulation via lymphatic system
Lipids
Significant reductions in dietary lipid compromise exercise performance.
Low fat vs. High fat diet: Greater injury rate with low-fat
Lipids are necessary to obtain essential fatty acids and fat-soluble vitamins.
Triglycerides as Energy Source
TG• Higher energy density than CHO (9 kcal/g vs.
4)• Also provides more ATP per molecule
• Glucose – 36• Fat – ~400
Limitations of FA Oxidation
Time• Fat has to be broken down and mobilized
from fat cells• Transported to active muscle• Taken up into the muscle• Activated• Transported into the mitochondria• B-oxidation• Krebs• ETC
Limitations of FA Oxidation
Control of FA oxidation• Aerobic training status• Habitual dietary intake• Ingestion of CHO and fat
• Before• During
• Relative and absolute exercise intensity• This is the key
Triglycerides as Energy Source
Triglycerides (adipose) – hydrolyzed• Lipolysis – TG lipase• Hormone sensitive
• Activated by epinephrine, glucagon• Inhibited by elevated plasma glucose, insulin
FA, glycerol - Released into circulation• FA bound with albumin • Glycerol to liver
Oxidation of FA
β-oxidation• Fatty acyl-CoA • 16C fatty acid• C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C• Essentially converted to acetyl-CoA
molecules• TCA cycle
Lipid Metabolism -Exercise Intensity (cont)
25% VO2
• Mostly plasma FA• Majority of energy needs
65% VO2
• Peak for fat metabolism• Closer to 50/50
85% VO2
• Decline in FA oxidation• Insufficient blood flow • Insufficient albumin
• Increased rate of glycogenolysis
Exercise Intensity
>85% VO2max
• Reduced lipolysis Romijn (1995)
• Lipid infusion, 30 min, 85% VO2max
• Partial restoration of FA oxidation (up 27%)• Still less than at 65% VO2max
• FA oxidation impaired-failure of lipolysis
• Upper limit of TG lipolysis – sets FA oxidation
Exercise Intensity
Coyle (1997)• CHO metabolism regulates FA oxidation• Pre exercise CHO ingestion • Increased rate of glycogenolysis
• Inhibits FA oxidation• Inhibiting entry of LCFA into mitochondria • Probably due to competition
Enhance Fat Oxidation-Exercise
Caffeine• High intensity-short term• Prolonged moderate intensity
Effects of caffeine• Central nervous system stimulant• Reduces perception of effort
Enhance Fat Oxidation-Exercise
5 to 9 mg/kg Some glycogen sparing Some prolonged endurance exercise Summary
• Responses variable• Most likely to occur > 6 mg/kg
However, fat oxidation is unchanged
Enhance Fat Oxidation-Exercise
Fat feeding before exercise• Evident only during early stages of exercise• More FA oxidation during 20 min of exercise
• But no enhanced exercise performance
Enhance Fat Oxidation-Exercise
LCFA, MCFA ingestion during exercise• Increased serum TG concentrations• No effect on FA oxidation• Time to exhaustion-similar
Enhance Fat Oxidation-Exercise
High fat (>60%), low CHO diets (<20%)• Retool mitochondria – FA oxidation• Can increase FA oxidation by ~ 40%• Does not alter rate of muscle glycogen
utilization• Doesn’t improve prolonged moderate-
intensity exercise• Increases CVD risk
Enhance Fat Oxidation-Exercise
The Zone diet - 40/30/30• Athlete taps into body fat• No clear evidence of any benefit• Some evidence of impaired performance
Enhance Fat Oxidation-Exercise
L-carnitine supplementation• Needed for transport of LCFA into mito• 2-5 g/day for 5 days to 4 weeks• No effect on fuel utilization
• Rest or exercise
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