Lose weight slowly to keep muscle
A moderate calorie deficit, about half a percent to one percent of body weight per week, preserves more muscle than an aggressive one, and large deficits raise the risk of lost strength, illness, and injury.
In plain English
Losing weight slowly, roughly half a percent to one percent of body weight a week, keeps muscle and training intact. Crash deficits cost muscle and raise the odds of getting hurt or run-down.
Why it works
Large energy deficits suppress muscle protein synthesis and recovery; moderate deficits leave enough energy to train hard and hold onto muscle.
What it means in practice
Guide cutting runners toward a moderate rate of loss (about 0.5-1% of body weight per week) rather than the largest deficit they can stand, and steer leaner athletes toward the conservative end.
The evidence
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Training in an energy deficit impaired gains in lean mass relative to training in energy balance, but strength gains were comparable between conditions. The meta-regression suggested deficits beyond about 500 kcal/day prevented lean-mass gains, so people building muscle should avoid prolonged large deficits and those preserving muscle during weight loss should keep deficits below roughly 500 kcal/day.
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Recommends losing about 0.5-1.0% of body weight per week, with more conservative deficits as the athlete gets leaner. Protein of roughly 2.3-3.1 g/kg of fat-free mass per day (about 1.6-2.4 g/kg body weight) is advised, with carbohydrate set to support training (about 2.5 g/kg/day or more) and fat kept above roughly 0.5 g/kg/day.
Why we call confidence medium
A meta-regression points to lean-mass gains being prevented beyond roughly a 500 kcal/day deficit, and athlete-nutrition reviews converge on 0.5-1% of body weight per week. The precise thresholds vary by individual and leanness.
Where it applies
Adults, including athletes, losing weight while training.
Does not apply to: clinically supervised rapid weight loss for medical reasons.
Last reviewed 2026-06-20. See how we score.