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.  Western diet – 35%  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

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% 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

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

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)