Exercise Nutrition and Carbohydrate Dynamics

Exercise Nutrition

• Exercise nutrition focuses on the type and quantity of fluids and food consumed by athletes
• Athletes need to fuel their bodies adequately because exercise degrades the body, requiring nutrition for repair and recovery
• The body needs protein to rebuild muscle, carbohydrate for energy and fat burning, vitamins and minerals for electrolyte balance and antioxidants to stop free radicals and oxidative stress caused by exercise.
• Optimal nutrition in exercise can delay fatigue, enhance energy levels, lead to better and faster recovery, reduce soreness and inflammation, enhance immunity, and minimize injury risk

Carbohydrate Dynamics in Exercise

• The body needs to maintain blood glucose levels during exercise, which is achieved through liver glycogen breakdown into glucose for release into the bloodstream
• Carbohydrate stores are essential for sustained exercise but once exhausted, the body relies on fats for energy which lower exercise intensity

Carbohydrate Timing

• Pre-exercise: consume a high carbohydrate meal (1-4 grams/kg) 1-4 hours before exercise to optimize glycogen stores, maintain blood sugar, optimize hydration, and avoid hunger
• During Exercise (longer than 90 minutes): Take 30-60 grams of carbohydrates per hour (e.g., glucose or maltodextrin) to spare muscle glycogen, prevent hypoglycemia, and improve performance and delay fatigue
• Post-Exercise: consume 1-1.5 grams of carbohydrates/kg within 30 minutes to accelerate recovery and replace muscle glycogen stores

Carbohydrate Loading

• Carbohydrate loading is a strategy used by endurance athletes to increase muscle glycogen stores before competition and fight fatigue
• It occurs in 2 phases:
  • Glycogen depletion phase: deplete glycogen stores through dietary manipulation, moderate calorie restriction, and increased training
  • Glycogen replenishment phase: reduce training intensity and increase carbohydrate intake

Applying Carbohydrate Loading

• Begin 6 days before competition
• Depletion phase (3 days): Maintain high training intensity, eat 5-6 meals daily, and consume 20% fats, 60% protein, and 20% carbohydrates
• Loading phase (3 days): Reduce training, significantly increase carbohydrate intake (10-12 grams/kg/day), and consume 15% fats, 15% protein, and 70% carbohydrates.

Proteins and Their Role in Exercise

• Proteins are essential for muscle repair, recovery, and growth
• During exercise, particularly resistance training, muscle fibers are damaged, and protein is necessary for repair and building stronger muscle tissue

Recommended Protein Intake

• General population: 0.8 grams of protein per kilogram of body weight per day
• Endurance athletes: 1.2-1.4 grams per kilogram of body weight per day, particularly during prolonged activities
• Strength athletes: 1.6-2.0 grams per kilogram of body weight per day due to increased muscle damage and the need for repair and growth during resistance training

Protein Dynamics in Exercise

• Exercise, especially resistance training, increases muscle protein breakdown, requiring post-exercise protein consumption to promote muscle protein synthesis for recovery and hypertrophy
• The balance between muscle protein breakdown and synthesis determines muscle growth or loss
• During prolonged exercise, amino acids from protein can be oxidized for energy when carbohydrate stores are low

Timing and Quality of Protein Intake

• The success of achieving a positive muscle protein balance depends on the amino acid composition of the food ingested, amino acid concentration in the blood supplying muscle cells, and the timing of the protein feeding
• Pre-exercise: Moderate protein intake helps to minimize muscle breakdown
• Post-exercise: Consuming 20-30 grams of high-quality protein within 30 minutes to 2 hours post-exercise with carbohydrates accelerates recovery and promotes muscle repair

Lipids and Their Role in Exercise

• Lipids are a concentrated source of energy, particularly important for long-term endurance activities when carbohydrate stores are depleted
• Fats are essential for cell membrane integrity, hormone production, and fat-soluble vitamin absorption (A, D, E, and K).
• Omega-3 fatty acids (DHA and EPA) have beneficial effects on the cardiovascular system, act as inflammatory moderators, and enhance strength and aerobic performance

Recommended Lipid Intake

• General population: 20-35% of daily caloric intake (0.5-1.5 grams/kg/day) should come from fats, focusing on healthy fats like monounsaturated and polyunsaturated fats
• Athletes: Fat intake should generally fall between 20-35% of daily calories, but endurance athletes may consume slightly more for long-duration activities

Lipid Dynamics During Exercise

• Triglyceride Storage and Mobilization: Triglycerides stored in adipose tissue are mobilized and broken down into free fatty acids (FFAs) during exercise
• Free fatty acids are transported to mitochondria, where beta-oxidation occurs, producing acetyl-CoA that enters the Krebs cycle to produce ATP

Lipids and Exercise

• At rest and low-intensity exercise, lipids are the primary fuel source
• During prolonged exercise, the body increases its reliance on fat oxidation to sustain energy because glycogen stores are depleted.