Nutritional Recommendations for the Physically Active Person
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Transcript of Nutritional Recommendations for the Physically Active Person
Nutritional Recommendations for the Physically Active Person
Chapter 7Part 2
Lipids Stored triglycerides
• Muscle• Adipose
Nutritional strategies to improve FFA oxidation
Lipids To promote good health, lipid intake
should probably not exceed 30% of the diet’s energy content. Western diet – 35%
100-150 g/dOf 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
Storage Sites
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
Fatty Acid Transport
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
Exercise Intensity
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
Summary/Recommendations Lack of scientific testing
• The Zone Diet Well investigated-no benefit
• L-carnitine Some benefit to performance (not FA ox)
• Caffeine (6 mg/kg)