Research

Energy balance

Deliberate overfeeding consistently induces weight gain in normal-weight adults, with approximately 38-44% of the gain consisting of lean body mass (LBM) rather than just fat.

If you are a normal-weight adult and you consistently eat more calories than you burn, you will gain weight. About 40% of that gain will be lean tissue (muscle, organs), not just fat. This happens regardless of whether you are male or female, or whether you are naturally thin or slightly overweight. There is no 'magic' resistance to weight gain in thin people.

GoodSupportsHIGH confidence
Based on the observed ratio of the regression slopes for Figs. 1 and 2 (0.0114/0.0297 = 0.384), the average composition of the weight gain was 38 % lean and 62% fat; based on means, these values are 44% lean and 56% fat.
Gilbert B. Forbes et al. · British Journal Of Nutrition · 1986

Why this rating

Controlled clinical environment, rigorous body composition assays (40K counting, densitometry), and large combined dataset (n=48).

Source

Deliberate overfeeding in women and men: energy cost and composition of the weight gain

Gilbert B. Forbes et al. · British Journal Of Nutrition · 1986

DOI 10.1079/bjn19860080

clinical_trial · n=15Cited 169×
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DOI resolved against Crossref · corpus check 2026-06-10

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