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Nutritional Recommendations for the Physically Active Person

Nutritional Recommendations for the Physically Active Person. Chapter 7 Part 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.

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Nutritional Recommendations for the Physically Active Person

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  1. Nutritional Recommendations for the Physically Active Person Chapter 7 Part 2

  2. Lipids • Stored triglycerides • Muscle • Adipose • Nutritional strategies to improve FFA oxidation

  3. 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.

  4. Lipids • Long chain FA (LCFA) • C14-C22 • Medium chain FA (MCFA) • C8-C10 • Short chain FA (SCFA) • 6C or less

  5. Lipids • Digestion • Gastric lipase • Converts TG to FA, diacylglycerols • Pancreatic lipase • Somewhat specific to LCFA (>10C)

  6. Lipids • Triglyceride hydrolysis • 3 FFA • acylglycerol • Slightly water soluble • Incorporate into micelles • Transport vehicles

  7. Lipids • MCFA • Absorbed into portal blood – liver • LCFA • Bypass liver • Released in form of chylomicrons (lipoproteins) • To circulation via lymphatic system

  8. 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.

  9. 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

  10. 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

  11. 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

  12. Storage Sites

  13. 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

  14. Fatty Acid Transport

  15. 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

  16. Exercise Intensity

  17. 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

  18. 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

  19. 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

  20. Enhance Fat Oxidation-Exercise • Caffeine • High intensity-short term • Prolonged moderate intensity • Effects of caffeine • Central nervous system stimulant • Reduces perception of effort

  21. 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

  22. 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

  23. Enhance Fat Oxidation-Exercise • LCFA, MCFA ingestion during exercise • Increased serum TG concentrations • No effect on FA oxidation • Time to exhaustion-similar

  24. 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

  25. 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

  26. 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

  27. 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)

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