Mixed
Combining resistance exercise training (RET) with adequate protein intake (≥1.2 g/kg/day) during a very low-calorie diet (VLCD) preserves skeletal muscle mass, whereas VLCD alone results in significant lean mass loss.
If you are on a strict low-calorie diet, you must lift weights and eat enough protein (at least 1.2 grams per kilogram of body weight daily) to keep your muscle. Doing just the diet without exercise or protein will cause you to lose muscle mass along with fat.
When adhering to a VLCD, RET will be the most powerful nonpharmacological stimulus for maintaining muscle mass and attenuating muscle atrophy. When RET is combined with a higher protein intake (≥1.2 g/kg), they work synergistically to promote lean mass sparing during periods of an energy deficit.
Why this rating
The paper cites specific randomized controlled trials (Jo et al., Longland et al.) showing preserved or increased lean mass, though it is a review paper.
Source
The impact and utility of very low-calorie diets: the role of exercise and protein in preserving skeletal muscle mass
Tom A.H. Janssen et al. · Current Opinion in Clinical Nutrition & Metabolic Care · 2023
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