Context: While popular weight-loss medications have raised concerns about lean mass loss, the normative effects of nonpharmacologic weight loss on body composition remain unclear.
Objective: We assessed how the extent of weight loss from dietary changes affects lean mass and bone mineral content (BMC) in women and men.
Methods: We conducted a secondary analysis of the DIETFITS trial (NCT01826591), a randomized controlled study with 609 adults (aged 18-50, body mass index [BMI] 28-40). Data from 323 participants (200 women, 123 men) who lost weight at 6 months and had dual-energy x-ray absorptiometry (DXA) assessments at baseline, 6 months, and 12 months were analyzed. Participants were stratified as follows: less than 5% (n = 102), 5% to 9% (n = 121), and 10% or more (n = 100). The primary outcome was the percentage of lean mass lost relative to total weight loss (%LML).
Results: Baseline mean BMI (33 kg/m2) was similar across weight-loss groups and sexes. Mean percentage weight loss was greatest at 6 months (2.9%, 7.3%, 14.6% in those losing <5%, 5%-9%, and ≥10%, respectively) and was similar between sexes. %LML varied widely with weight loss of less than 5% but plateaued with greater loss. Men had higher %LML than women when weight loss was 5% or greater (median [interquartile range], 33% [24-41] vs 28% [17-36]; P < .001). All groups, except for women losing 10% or more, significantly regained weight and fat mass at 12 months, while BMC continued to decline.
Conclusion: Contrary to our hypothesis, %LML plateaus with greater weight loss. Moreover, men experience greater %LML than women. The decline in BMC despite weight regain warrants further investigation.
Keywords: DXA; body composition; fat mass; lean mass; weight loss.
© The Author(s) 2026. Published by Oxford University Press on behalf of the Endocrine Society.