Metformin added to lifestyle intervention for physical function in older adults with obesity (DEMFOS trial): a randomised controlled trial

BACKGROUND: Obesity in older adults is associated with functional decline and increased risk of disability. Lifestyle interventions improve physical function, but the role of metformin as an adjunct to lifestyle intervention in this population remains unclear. In this randomised clinical trial, we evaluated whether metformin enhances the effects of an intensive lifestyle intervention on physical function in older adults with obesity. METHODS: ) were randomly assigned to intensive lifestyle intervention (weight-management and exercise training) plus placebo, intensive lifestyle intervention plus metformin, or healthy lifestyle (diet education) plus metformin groups. The primary outcome was change in the modified physical performance test score at 6 months. The primary analysis was by intention-to-treat. FINDINGS: Of 221 participants assessed for eligibility between March 30, 2021, and Dec 12, 2024, 114 were included in this study (mean age 72·8 years [SD 5·2]; 101 [89%] men and 13 [11%] women). 64 (56%) participants were White, 50 (44%) were Black, and 15 (13%) were Hispanic or Latino. Changes in physical performance test differed between groups (group-by-time interaction p<0·0001). At 6 months, physical performance test improvement was greater in the intensive lifestyle plus metformin group than in the healthy lifestyle plus metformin group (mean difference 2·5 points, 95% CI 1·2-3·8; p=0·0002), whereas there was no difference between the intensive lifestyle plus metformin and intensive lifestyle plus placebo groups (0·1 points, -1·2 to 1·4; p=0·92). Serious adverse events were infrequent and not attributed to the study interventions. INTERPRETATION: Our findings suggest that in older adults with obesity undergoing intensive lifestyle intervention, metformin does not provide additional improvement in physical function. These results support prioritising lifestyle-based strategies to improve functional outcomes in this population. FUNDING: US Department of Veterans Affairs.