Strength training keeps muscle while you cut
When a runner loses weight, resistance training protects muscle, so more of the loss comes from fat rather than lean tissue.
In plain English
Dieting alone strips some muscle along with fat. Keeping resistance training in the plan prevents most of that muscle loss; in one analysis, about 93% of it.
Why it works
Resistance training signals the body to hold onto muscle protein even when energy is scarce, preserving the lean tissue that energy restriction alone would erode.
What it means in practice
A runner trying to lose weight should keep strength training in the plan rather than swap it for extra cardio. This protects muscle, strength, and metabolism while the fat comes off.
The evidence
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Adding resistance training to caloric restriction prevented almost all of the lean-mass loss seen with dieting alone, while fat-mass and total-mass reductions were similar between groups. Resistance training offset roughly 93.5% of the muscle loss caused by caloric restriction.
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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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Resistance training combined with caloric restriction was the most effective approach for reducing body fat percentage and total fat mass, while resistance training attenuated the lean-mass loss that usually accompanies weight loss. Resistance training alone modestly increased lean mass.
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Adding exercise to energy restriction improved fitness, strength, and fat loss and better preserved fat-free mass than dieting alone. Across studies the decrease in lean mass was smaller (roughly 1-2% less) when exercise accompanied the diet, and the review noted that lean-mass loss should stay a small share of total weight lost.
Why we call confidence high
Several meta-analyses across dieting populations show resistance training markedly reduces the lean-mass loss that occurs with energy restriction alone. Most data are in older or overweight adults, so the exact effect in lean runners is less certain.
Where it applies
Adults losing weight in an energy deficit; strongest evidence in older and overweight populations, with supporting athlete data.
Does not apply to: very lean athletes at extreme deficits, where muscle loss is harder to prevent.
Last reviewed 2026-06-20. See how we score.