Nutrition and Hydration
Domain 3 - Nutrition and Hydration
This domain tests practical fueling and hydration decisions: energy availability, carbohydrate and protein needs, timing, sweat-rate calculation, and sodium replacement. Expect scenario questions rather than isolated definitions.
Core rules and concepts
- Energy availability = energy intake − exercise energy expenditure, expressed per kilogram of fat-free mass. Chronic low energy availability raises risk of relative energy deficiency in sport (RED-S).
- Carbohydrate needs scale with training load, commonly about 3–10 g/kg/day; higher loads need the upper end.
- Protein for adaptation is commonly 1.6–2.2 g/kg/day, distributed across meals at roughly 0.25–0.3 g/kg per meal.
- Fat should not be driven chronically low; roughly 20–25% of energy supports hormone and cell function.
- Sweat rate = (pre-exercise body mass − post-exercise body mass + fluid consumed) ÷ exercise hours.
- Replace about 125–150% of body-mass deficit over the next 2–4 hours; include sodium when sweat is salty or exercise is long.
Worked example
A 70 kg athlete loses 1.2 kg over a 2-hour session and drinks 0.5 L. Sweat rate = (1.2 + 0.5) ÷ 2 = 0.85 L/hour. Replacement = 1.2 kg × 1.25–1.5 = 1.5–1.8 L over 2–4 hours. Reasoning: body-mass change already includes the fluid consumed, so add intake back before dividing by time.
Traps that cost marks
- Blaming cramps only on sodium; fatigue, intensity, and individual variation matter.
- Recommending very high protein without evidence.
- Using “clean eating” as a substitute for adequacy and timing.
- Forgetting that rapid weight loss can reflect dehydration, not fat loss.
Exam takeaway
Calculate, then contextualize: training load, sweat losses, and total energy availability.