Nutritional Strategies for Enhanced Lipid Oxidation During Exercise

Fat vs. CHO

CHO is both aerobic and anaerobic, BUT it has limited stores. It does, however, have a greater energy yield per unit of O2 (fat is about 10% less).

Sparing CHO

Sparing CHO by upregulating lipid oxidation should be advantageous. This leads to:

• More lipid oxidation
• Decreased sympathetic nervous system activity (recruitment of CHO)
• Increased mitochondrial volume and enzymatic adaptations
• Reduction in signals that activate major CHO metabolic enzymes

In lower exercise intensity, more FFA and TG are present in plasma. The more intense the exercise becomes, the more glycogen/glucose is used. At ~62% of VO2 max, the highest lipid oxidative rate is experienced.

Nutritional Strategies to Improve Lipid Oxidation

• High-fat diets: long term vs. short term
• Smart training: manipulating CHO availability -> train low, compete high
• Medium-chain TG/medium-chain FFA
• Fat burners -> caffeine/carnitine

Long Fatty Acids vs. Medium Fatty Acids

• LFA: slow gastric emptying – incorporation into chylomicrons
• MCFA: rapid gastric emptying and absorption (like glucose) – do not need carnitine shuttle – may lead to gastrointestinal complaints, quickly oxidized, however, the contribution to EE is low ~3-7% no performance effect.

Caffeine: metabolizes fatty acids from TG stores, adrenaline, SN

L-Carnitine: needed to transport FFA into mitochondria. At 50% reduces glycogen breakdown, at 80% VO2max no longer effective

Long Term (7 Week) High-Fat Diet:

• Endurance performance is better when finally exposed to a carbohydrate-rich diet.
• Increased FA transport and oxidation; reduced CHO metabolism, saving the glycogen.
• Improved lipid metabolism
• Impaired endurance exercise performance
• Low glycogen, CHO metabolism
• Unable to train hard, impaired adaptation

Short Term High-Fat Diet:

• NO effect pre-exercise meal, leads to low glycogen and no increased lipid oxidative capacity.
• SWITCHING high fat with high carb leads to more fat oxidation and less carb oxidation.
• Increase muscle triglyceride stores
• Reduce glycogen utilization
• Improve fat oxidation
• Improved lipid oxidation after > 3 days
• No performance effect

NOTA: More CPT-1 (carnitine), less GLUT4, more CD36/FAT, more HSL, less glycerol in muscle fiber, more triglycerides in fibers, less PDH leading to less CHO oxidation during exercise.

Training twice every second day enhances time until exhaustion, resting muscle glycogen concentration, and CS activity. But not better performance.

Training Strategies

• Low CHO diets
• Twice-a-day training
• Overnight fast
• Prolonged training – overnight fast/withholding CHO
• Withholding CHO first hours of recovery