Once total daily energy expenditure is known, athletes manipulate calorie intake to match their training goals. A caloric surplus — consuming more calories than expended — is used for muscle gain, with a moderate surplus of 250–500 kcal per day above TDEE promoting muscle growth while minimizing fat accumulation. A caloric deficit — consuming fewer calories than expended — is necessary for fat loss, with a moderate deficit of 300–500 kcal per day below TDEE promoting fat loss while preserving muscle mass when combined with adequate protein and resistance training.
It is important to distinguish between weight loss and fat loss. Weight loss includes loss of fat, muscle, water, and glycogen, while fat loss specifically targets adipose tissue. To maximize fat loss while preserving muscle, athletes should maintain a moderate caloric deficit, keep protein intake high at 2.0+ g/kg, perform resistance training, and aim to lose 0.5–1% of body weight per week. However, as dieting progresses, the body undergoes metabolic adaptation (adaptive thermogenesis), reducing energy expenditure beyond what is predicted by weight loss alone. This includes decreased BMR, reduced NEAT, improved movement efficiency, and hormonal changes such as lower leptin and thyroid hormone levels, all of which make continued fat loss progressively harder.
Planned diet breaks and refeeds can help counteract these adaptations. Diet breaks are planned periods of 1–2 weeks of eating at maintenance calories during a fat loss phase, while refeeds are shorter 1–2 day periods of increased carbohydrate intake. Both may help restore leptin levels, reduce psychological stress, and mitigate metabolic slowdown. To calculate macronutrient ratios, athletes first determine calorie needs via TDEE, then set protein at 1.6–2.2 g/kg, fat at 20–35% of total calories, and fill the remaining calories with carbohydrates. For example, an 80 kg athlete needing 3000 kcal might consume 160 g protein (640 kcal), 83 g fat (750 kcal), and 403 g carbohydrates (1610 kcal). Periodized nutrition takes this further by adjusting calorie and macronutrient intake based on training phase: more carbohydrates during high-volume training, more protein during strength phases, and moderate intake during the off-season.