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%

100-150 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% 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)