Read the guide · Nutrition
Building muscle: how much to eat and what to expect
Building muscle requires eating above energy expenditure, but the curve is not linear: beyond a modest surplus, the excess turns into fat without accelerating muscle growth. The useful range is 5 to 15% of energy expenditure, with weight gain of up to about 0.5% of body weight per week. Letz applies 10% as default, capped between 150 and 300 kcal, and the weight forecast alerts you when the pace exceeds this range instead of celebrating any number on the scale.
Numbers derived from this rule
| Parameter | Range | Weight | Rule |
|---|---|---|---|
| Weekly weight change | 0.5–1 % of body weight/week1 variant by context | 60% | Lose 0.5 to 1% of body weight per week; gain up to about 0.5% per week when the goal is mass.Rate of weight loss · Calorie surplus for muscle gain |
| Calorie surplus | 5–15 % of energy expenditure | 50% | A modest surplus of 5 to 15% of energy expenditure supports hypertrophy without accumulating unnecessary fat.Calorie surplus for muscle gain |
| Dietary fat | 20–35 % of calories | 50% | Fat between 20 and 35% of calories; below 20% impairs hormones and adherence.Calorie surplus for muscle gain · Carbohydrates and Workout Performance |
| Daily protein | 1.6–2.2 g/kg/day2 variants by context | 90% | 1.6 to 2.2 g/kg/day for those who train; in a deficit, the upper end of the range protects lean mass.Protein and Training Adaptation · Higher Protein Intake During a Calorie Deficit |
| Calorie deficit | 10–25 % of expenditure1 variant by context | 80% | Deficit of 10 to 25% of expenditure, aiming for a loss of 0.5 to 1% of body weight per week; faster rates cost lean mass and metabolism.Rate of weight loss · Higher Protein Intake During a Calorie Deficit · Weight change is dynamic |
Rules and studies
- 01Calorie surplus for muscle gainA modest surplus supports hypertrophy; large surpluses primarily increase fat gain. Beginners and individuals with higher body fat can build muscle even without a surplus.Letz sets the surplus at 10% of energy expenditure, between 150 and 300 kcal, and the weight trend projection flags when weekly gain exceeds the target range.
- 02Protein and Training AdaptationSufficient protein can support gains in lean mass and strength alongside training; the response varies and does not increase indefinitely with higher intakes.The Letz protein target uses 1.6 to 2.2 g/kg depending on the goal, calculated using whichever is lower between current weight and target weight.
- 03Weight change is dynamicThe body's weight response to sustained changes in energy intake is gradual and involves adaptations; projections should use curves and ranges rather than a rigid linear rule.The weight forecast in Progress uses the observed trend and an uncertainty range, never a promised target date.