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)