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Nutritional Recommendations for the Physically Active Person Chapter 7 Part 2
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Lipids Stored triglycerides Muscle Adipose Nutritional strategies to improve FFA oxidation
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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.
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Lipids Long chain FA (LCFA) C14-C22 Medium chain FA (MCFA) C8-C10 Short chain FA (SCFA) 6C or less
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Lipids Digestion Gastric lipase Converts TG to FA, diacylglycerols Pancreatic lipase Somewhat specific to LCFA (>10C)
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Lipids Triglyceride hydrolysis 3 FFA acylglycerol Slightly water soluble Incorporate into micelles Transport vehicles
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Lipids MCFA Absorbed into portal blood – liver LCFA Bypass liver Released in form of chylomicrons (lipoproteins) To circulation via lymphatic system
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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.
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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
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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
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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
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Storage Sites
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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
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Fatty Acid Transport
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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
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Exercise Intensity
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Lipid Metabolism - Exercise Intensity (cont) 25% VO 2 Mostly plasma FA Majority of energy needs 65% VO 2 Peak for fat metabolism Closer to 50/50 85% VO 2 Decline in FA oxidation Insufficient blood flow Insufficient albumin Increased rate of glycogenolysis
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Exercise Intensity >85% VO 2max Reduced lipolysis Romijn (1995) Lipid infusion, 30 min, 85% VO 2max Partial restoration of FA oxidation (up 27%) Still less than at 65% VO 2max FA oxidation impaired-failure of lipolysis Upper limit of TG lipolysis – sets FA oxidation
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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
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Enhance Fat Oxidation-Exercise Caffeine High intensity-short term Prolonged moderate intensity Effects of caffeine Central nervous system stimulant Reduces perception of effort
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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
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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
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Enhance Fat Oxidation-Exercise LCFA, MCFA ingestion during exercise Increased serum TG concentrations No effect on FA oxidation Time to exhaustion-similar
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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
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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
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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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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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