Nutrition Fundamentals for Athletes
Evidence-based guide to fueling performance, recovery, and adaptation
Nutrition as Performance Infrastructure
Nutrition isn't about "eating healthy"—it's about providing the substrate for energy production, tissue repair, immune function, and hormonal balance. For athletes, nutrition determines whether training adaptations occur, performance peaks, or the body breaks down.
This module covers the fundamentals: macronutrients, energy balance, meal timing, and nutrient density. Separate modules address race-day fueling, recovery nutrition, and hydration.
The Three Macronutrients
Carbohydrates: Primary Fuel for High-Intensity Work
Function
Stored as glycogen in muscles and liver. During moderate-to-high intensity exercise (≥60% VO2max), carbohydrate oxidation provides the majority of energy. Limited stores (~500g total, ~2000 kcal) mean they must be replenished daily.
Daily Requirements
- • Low-intensity athletes (<1 hr/day): 3-5 g/kg bodyweight
- • Moderate training (1-2 hrs/day): 5-7 g/kg
- • High-volume endurance (>2 hrs/day): 7-10 g/kg
- • Ultra-endurance (4+ hrs/day): 10-12 g/kg
Example: 70kg runner training 1.5 hrs/day → 350-490g carbs/day (1400-1960 kcal)
Sources
Complex (Prioritize):
- • Oats, quinoa, brown rice
- • Sweet potatoes, whole grains
- • Legumes, beans
Simple (Strategic Use):
- • Sports drinks, gels (during)
- • Fruit, honey (post-training)
- • White rice/bread (quick refuel)
Key Insight: Carbs aren't "bad"—they're essential for high-intensity performance. The "low-carb athlete" can work for ultra-endurance at low intensities, but impairs VO2max efforts.
Protein: Tissue Repair & Adaptation
Function
Provides amino acids for muscle protein synthesis (MPS), immune function, enzyme production, and hormone synthesis. Training increases protein requirements significantly above sedentary norms.
Daily Requirements
- • Endurance athletes: 1.2-1.6 g/kg bodyweight
- • Strength/power athletes: 1.6-2.2 g/kg
- • During calorie deficit: Up to 2.4 g/kg (preserve lean mass)
- • Recovery from injury: 2.0-2.5 g/kg
Example: 70kg triathlete → 84-112g protein/day minimum (336-448 kcal)
Timing & Distribution
More important than total amount: Distribute evenly across 4-5 meals to maximize MPS.
- • Per meal: 20-40g protein (0.25-0.4 g/kg)
- • Post-training: 20-40g within 2 hours (critical window)
- • Before bed: 30-40g slow-digesting (casein, Greek yogurt)
Sources
Animal (Complete):
- • Chicken, turkey, fish
- • Eggs, Greek yogurt
- • Lean beef, whey protein
Plant-Based:
- • Legumes, lentils, tofu
- • Quinoa, tempeh
- • Pea/rice protein powder
Key Insight: More protein ≠ better beyond ~2.2 g/kg. Excess is oxidized for energy or converted to fat. Focus on distribution and timing.
Fats: Hormones, Inflammation, & Fuel
Function
Essential for hormone production (testosterone, estrogen, cortisol), cell membrane integrity, vitamin absorption (A, D, E, K), and low-intensity fuel substrate. Omega-3s reduce inflammation.
Daily Requirements
- • General athletes: 0.8-1.2 g/kg bodyweight (minimum)
- • Or 20-35% of total calories
- • Never below: 0.5 g/kg (hormonal dysfunction risk)
Example: 70kg athlete → 56-84g fat/day (504-756 kcal)
Types & Sources
✓ Prioritize (Unsaturated):
- • Omega-3: Salmon, sardines, walnuts, flaxseed, chia (anti-inflammatory)
- • Monounsaturated: Olive oil, avocado, almonds
⚠ Moderate (Saturated):
- • Red meat, butter, coconut oil (<10% of calories)
✗ Avoid (Trans Fats):
- • Processed foods, fried foods, margarine (pro-inflammatory)
Key Insight: Fat isn't "slow fuel" that limits performance—it's essential for health. Low-fat diets (<15% calories) impair testosterone and estrogen production.
Energy Balance & Body Composition
The Energy Balance Equation
Energy In (Calories Consumed) - Energy Out (Expenditure) = Change in Body Mass
Caloric Surplus (Building)
- • Purpose: Build muscle, support high training volumes
- • Surplus: +200-500 kcal/day above maintenance
- • Risk: Excess fat gain if surplus too large or protein inadequate
Caloric Maintenance (Sustaining)
- • Purpose: Maintain body composition during competition phases
- • Balance: Intake = Expenditure
- • Most athletes should be here most of the time
Caloric Deficit (Fat Loss)
- • Purpose: Reduce body fat for power-to-weight optimization
- • Deficit: -300 to -500 kcal/day (max ~1% body weight loss/week)
- • Critical: High protein (2.0-2.4 g/kg) to preserve muscle
- • Risk: Performance decline, hormonal disruption if too aggressive
Danger Zone: Low Energy Availability (LEA)
Energy Availability (EA) = (Calories In - Exercise Expenditure) / Fat-Free Mass
- • Optimal: >45 kcal/kg FFM/day
- • LEA (risk zone): <30 kcal/kg FFM/day
- • Consequences: Menstrual dysfunction, bone loss, immune suppression, injury
Never chronically restrict calories during heavy training blocks.
Nutrient Timing: When to Eat What
Pre-Training (2-4 hours before)
Goal: Top off glycogen, provide sustained energy, avoid GI distress
- • Carbs: 1-4 g/kg (higher for longer sessions)
- • Protein: 15-25g (slow digestion, MPS preparation)
- • Fat: Low-moderate (slows digestion)
- • Example: Oatmeal + banana + peanut butter + protein shake
During Training (>90 minutes)
Goal: Sustain blood glucose, delay glycogen depletion
- • Carbs: 30-60 g/hour (90-120g/hr for ultra-endurance)
- • Forms: Sports drinks, gels, chews, bars
- • No protein/fat needed during (delays absorption)
- • See dedicated Race Day Nutrition module for details
Post-Training (0-2 hours after)
Goal: Maximize glycogen resynthesis and muscle protein synthesis
- • Carbs: 1.0-1.2 g/kg (immediately post for glycogen)
- • Protein: 20-40g (maximize MPS)
- • Timing: Sooner = better, but 2-hour window is fine
- • Example: Chocolate milk, protein shake + fruit, rice bowl + chicken
See dedicated Recovery Nutrition module for detailed protocols
Before Bed
Goal: Sustain MPS overnight (8-hour fast)
- • Protein: 30-40g slow-digesting (casein ideal)
- • Sources: Greek yogurt, cottage cheese, casein shake
- • Evidence: Pre-sleep protein enhances overnight recovery
Micronutrients: Don't Neglect the Details
Vitamins and minerals don't provide energy, but they're cofactors for energy metabolism, immune function, and tissue repair. Deficiencies impair performance.
Critical for Athletes:
- • Iron: Oxygen transport (hemoglobin). Deficiency → fatigue, poor performance. Sources: red meat, spinach, lentils. Women at higher risk.
- • Calcium: Bone health, muscle contraction. 1200-1500mg/day. Sources: dairy, fortified plant milk, leafy greens.
- • Vitamin D: Bone metabolism, immune function, muscle function. 1000-2000 IU/day, supplement if serum <30 ng/mL.
- • Magnesium: Muscle relaxation, energy metabolism. 400-500mg/day. Sources: nuts, seeds, whole grains.
- • B-Vitamins: Energy metabolism cofactors. Sources: whole grains, meat, eggs.
- • Antioxidants (C, E): Reduce oxidative stress. Sources: fruits, vegetables. Don't megadose—may blunt training adaptations.
Best approach: Eat a varied, colorful diet with whole foods. Consider multivitamin if restrictive diet or blood tests show deficiencies.
Key Takeaways
- Carbs fuel high-intensity work—don't fear them (5-10 g/kg/day for endurance athletes)
- Protein distribution matters more than total—aim for 20-40g per meal, 4-5x/day
- Fat is essential for hormones—never go below 0.5 g/kg bodyweight
- Energy availability >45 kcal/kg FFM/day prevents RED-S and injury
- Post-training: 1-1.2g/kg carbs + 20-40g protein within 2 hours
Further Modules
- • Race Day Nutrition Strategy
- • Recovery Nutrition Protocols
- • Hydration for Performance
- • Fueling for Ultra-Endurance
Key Research References
- • Thomas, D. T., et al. (2016). Position of the Academy of Nutrition and Dietetics: Nutrition and Athletic Performance. Journal of the Academy of Nutrition and Dietetics, 116(3).
- • Burke, L. M., et al. (2011). Carbohydrates for training and competition. Journal of Sports Sciences, 29(S1).
- • Jäger, R., et al. (2017). International Society of Sports Nutrition Position Stand: protein and exercise. Journal of the International Society of Sports Nutrition, 14(1).
