Key Takeaways
- Carbohydrate recommendations for athletes: 5-7 g/kg/day for moderate training; 7-10 g/kg/day for high-volume training.
- Protein recommendations: 1.2-2.0 g/kg/day for athletes; optimal per-meal dose is 20-40g with leucine threshold of 2-3g.
- Fat should comprise 20-35% of total calories; very low-fat diets can impair hormone production and nutrient absorption.
- Glycogen storage capacity is approximately 400-500g (muscle) and 100g (liver); can be increased through carbohydrate loading.
- Protein timing around training (within 2 hours pre/post) supports muscle protein synthesis, though total daily intake matters most.
Macronutrients and Energy
Quick Answer: Athletes need 5-10 g/kg/day carbohydrates (based on training volume), 1.2-2.0 g/kg/day protein, and 20-35% of calories from fat. Energy balance determines body weight changes; create a 500 kcal/day deficit for ~1 lb/week weight loss or surplus for weight gain.
Carbohydrates
Carbohydrates are the primary fuel source for high-intensity exercise and are stored as glycogen in muscles and liver.
Carbohydrate Recommendations for Athletes
| Training Volume | Carbohydrate Intake |
|---|---|
| Light training (low intensity, skill-based) | 3-5 g/kg body weight/day |
| Moderate training (1 hour/day) | 5-7 g/kg body weight/day |
| High volume (1-3 hours/day moderate-high intensity) | 6-10 g/kg body weight/day |
| Extreme volume (4-5+ hours/day) | 8-12 g/kg body weight/day |
Glycogen Storage
| Location | Storage Capacity | Function |
|---|---|---|
| Muscle Glycogen | 400-500g (1,600-2,000 kcal) | Primary fuel for working muscles |
| Liver Glycogen | 100g (400 kcal) | Maintains blood glucose |
Key Point: Glycogen depletion leads to fatigue and decreased performance. Athletes must consume adequate carbohydrates to maintain glycogen stores.
Carbohydrate Loading
For endurance events lasting >90 minutes:
| Phase | Timing | Carb Intake |
|---|---|---|
| Loading Phase | 1-3 days before event | 10-12 g/kg/day |
| Pre-Event Meal | 3-4 hours before | 1-4 g/kg |
Glycemic Index Considerations
| GI Category | When to Use | Examples |
|---|---|---|
| High GI | During/immediately post-exercise | White bread, sports drinks, potatoes |
| Low GI | Pre-exercise (for sustained energy) | Oatmeal, whole grains, most fruits |
Protein
Protein is essential for muscle repair, growth, and numerous metabolic functions.
Protein Recommendations
| Population | Protein Intake |
|---|---|
| Sedentary adult | 0.8 g/kg/day |
| Endurance athlete | 1.2-1.4 g/kg/day |
| Strength/power athlete | 1.6-2.0 g/kg/day |
| During caloric restriction | Up to 2.3-3.1 g/kg/day (lean mass) |
Protein Quality
| Factor | Description | High-Quality Sources |
|---|---|---|
| Complete proteins | Contains all essential amino acids | Meat, fish, eggs, dairy, soy |
| Leucine content | Key amino acid for muscle protein synthesis | Whey, eggs, beef, chicken |
| Digestibility | How well protein is absorbed | Animal proteins > most plant proteins |
The Leucine Threshold
Muscle protein synthesis is optimally stimulated when:
- Per-meal protein intake: 20-40g (or 0.25-0.40 g/kg)
- Leucine content reaches: 2-3g per meal
Protein Timing
| Timing | Recommendation | Purpose |
|---|---|---|
| Pre-exercise | 20-40g, 2-3 hours before | Amino acid availability |
| Post-exercise | 20-40g, within 2 hours | Stimulate MPS, recovery |
| Throughout day | Distribute evenly across meals | Sustained MPS stimulation |
| Before sleep | 30-40g casein | Overnight recovery |
Important: Total daily protein intake is MORE important than precise timing. However, distributing protein across 4-5 meals optimizes muscle protein synthesis.
Fat
Fat is essential for hormone production, nutrient absorption, and serves as an energy source for low-intensity exercise.
Fat Recommendations
| Recommendation | Amount |
|---|---|
| Minimum intake | 20% of total calories |
| Recommended range | 20-35% of total calories |
| Avoid | <20% (can impair hormone production) |
Types of Dietary Fat
| Type | Effect | Sources |
|---|---|---|
| Saturated | Limit to <10% of calories | Meat, dairy, coconut oil |
| Monounsaturated | Heart-healthy, emphasize | Olive oil, avocados, nuts |
| Polyunsaturated | Essential fatty acids needed | Fish, flaxseed, walnuts |
| Trans | Avoid completely | Processed foods, hydrogenated oils |
Essential Fatty Acids
| Type | Recommendation | Sources |
|---|---|---|
| Omega-3 | 1-2g EPA+DHA daily | Fatty fish, fish oil supplements |
| Omega-6 | Adequate in most diets | Vegetable oils, nuts |
Energy Balance and Weight Management
Energy Balance Equation
Energy Balance = Energy Intake - Energy Expenditure
| State | Equation | Result |
|---|---|---|
| Positive balance | Intake > Expenditure | Weight gain |
| Negative balance | Intake < Expenditure | Weight loss |
| Energy balance | Intake = Expenditure | Weight maintenance |
Weight Change Guidelines
| Goal | Daily Caloric Adjustment | Expected Rate |
|---|---|---|
| Weight loss | -500 kcal/day deficit | ~1 lb/week loss |
| Weight gain | +250-500 kcal/day surplus | 0.5-1 lb/week gain |
| Rapid weight loss | >1,000 kcal deficit | Not recommended (muscle loss) |
Warning: Rapid weight loss (>1-2 lbs/week) typically results in muscle loss in addition to fat loss. Athletes should aim for gradual changes.
Components of Energy Expenditure
| Component | Contribution | Modifiable? |
|---|---|---|
| Basal Metabolic Rate (BMR) | 60-70% | Limited (affected by muscle mass) |
| Thermic Effect of Food (TEF) | 10% | Slightly (protein has highest TEF) |
| Physical Activity | 20-30% | Yes (training, daily activity) |
What is the recommended daily carbohydrate intake for an athlete engaged in moderate training (approximately 1 hour per day)?
What is the recommended daily protein intake range for strength and power athletes?
The leucine threshold for optimal muscle protein synthesis stimulation is approximately:
What is the MINIMUM recommended percentage of total calories from fat for athletes?