A small calorie surplus builds muscle with less fat

In one small trial, eating a little above what you burn built about as much muscle in trained lifters as eating a lot above it, and the bigger surplus mostly added fat. Other small trials found a larger surplus added a little more muscle along with more fat. Experts suggest starting around 360 to 480 calories a day above maintenance and adjusting from there.

Why it works

Extra energy supports building new muscle, but muscle can only be added so fast, so energy beyond that is likely stored as fat. The small trials fit this trade-off without measuring the limit.

The evidence

• Helms, E.R., Spence, A.J., Sousa, C. et al. (2023). Effect of Small and Large Energy Surpluses on Strength, Muscle, and Skinfold Thickness in Resistance-Trained Individuals: A Parallel Groups Design. Sports Medicine - Open.

  This 8-week trial split resistance-trained lifters into maintenance calories, a small 5% surplus, and a large 15% surplus while they trained 3 days a week (21 randomized, 17 completed after COVID-related dropout). Group comparisons found no difference in squat 1-rep max or in biceps, triceps or quadriceps muscle thickness, but the 15% surplus group gained more bench press 1-rep max than the other two groups and more skinfold thickness (fat) than the maintenance group. Across all lifters, faster body-mass gain strongly predicted skinfold (fat) gain and only weakly predicted biceps thickness gain. The authors concluded that faster gains in body mass mainly speed up fat gain rather than adding strength or muscle, a finding limited to this small, 8-week study of lifters with mixed training experience.

• Slater, G.J., Dieter, B.P., Marsh, D.J. et al. (2019). Is an Energy Surplus Required to Maximize Skeletal Muscle Hypertrophy Associated With Resistance Training. Frontiers in Nutrition.

  This review examined whether extra calories are needed to build muscle with resistance training. It concluded a surplus is not strictly required, since untrained, overweight, or obese people can add muscle even in a calorie deficit, but a modest surplus does help lean-mass gains, especially in already-trained lifters. It cautioned that overfeeding builds fat fast (in one 100-day overfeeding study in young lean men without training, about 2 kg of fat was gained for each 1 kg of lean mass), so it recommended starting conservatively with a surplus of about 1,500 to 2,000 kJ per day (roughly 360 to 480 calories) and adjusting based on body-composition results.

Why we call confidence low

Low: the evidence is a few very small trials and one expert review, and they do not all agree. Helms 2023 randomized 21 trained lifters (17 finished, 8 weeks) to maintenance, a 5 percent surplus or a 15 percent surplus: muscle thickness and squat strength did not differ between groups, bench strength favored the 15 percent group, and faster weight gain was mostly fat. Slater 2019's review recommends a modest surplus of roughly 1,500 to 2,000 kJ a day for trained lifters. Ribeiro 2019 (11 bodybuilders, 4 weeks) found higher intake gave a little more muscle and more fat, and Hatamoto 2024 (23 young men, no resistance training described) found body protein rose only with a 40 percent surplus.

Where it applies

Healthy resistance-trained adults