The three macronutrients — protein, carbohydrates, and fats — form the foundation of any sports nutrition plan. Each provides energy at a different density: protein and carbohydrates yield approximately 4 kcal per gram, while fat delivers about 9 kcal per gram. A calorie (technically a kilocalorie) is a unit of energy representing the heat needed to raise the temperature of 1 kg of water by 1 °C. In nutrition, calories quantify both the energy content of food and the energy expenditure of physical activity, making them the basic currency of any diet plan.
Understanding total energy needs is the first step in designing an athlete's diet. Total Daily Energy Expenditure (TDEE) is calculated as Basal Metabolic Rate (BMR) multiplied by an activity factor. The Mifflin-St Jeor equation is the most accurate method for estimating BMR: for males, \( \text{BMR} = 10 \times \text{weight (kg)} + 6.25 \times \text{height (cm)} - 5 \times \text{age} - 5 \), and for females the same formula minus 161. Activity factors range from 1.2 for sedentary individuals to 1.9 for very active athletes. Once TDEE is known, athletes can determine whether they need a caloric surplus, deficit, or maintenance to match their training goals.
The thermic effect of food (TEF) also plays a role in energy balance, representing the energy required to digest, absorb, and process nutrients. Protein has the highest thermic effect at 20–30% of calories consumed, followed by carbohydrates at 5–10% and fat at 0–3%. TEF accounts for roughly 10% of total daily energy expenditure. The thermic effect of exercise (TEE), including both structured workouts and non-exercise activity thermogenesis (NEAT), is the most variable component of energy expenditure, ranging from 15–30% of TDEE depending on activity level.