Nutritional
Recommendations for the
Physically Active Person
Chapter 7
Part 2
Lipids

Stored triglycerides

Nutritional strategies to improve FFA
oxidation
• Muscle
• Adipose
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)

Medium chain FA (MCFA)

Short chain FA (SCFA)
• C14-C22
• C8-C10
• 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

LCFA
• Absorbed into portal blood – liver
• 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

Romijn (1995)
• Reduced lipolysis
• 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

Effects of caffeine
• High intensity-short term
• Prolonged moderate intensity
• 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

However, fat oxidation is unchanged



• Responses variable
• Most likely to occur > 6 mg/kg
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

Well investigated-no benefit

Some benefit to performance (not FA ox)
• The Zone Diet
• L-carnitine
• Caffeine (6 mg/kg)