Metformin prevents weight gain in patients with type 2 diabetes (T2D). However, the mechanisms involved are still unknown. In this post hoc analysis of the HOME trial, we aimed to determine whether metformin affects energy intake. Patients with T2D were treated with 850mg metformin or received placebo added to insulin (1-3 times daily) for 4.3years. Dietary intake was assessed at baseline, after 1year and after 4.3years, according to the dietary history method. Among the 310 included participants, 179 (93 placebo, 86 metformin) completed all 3 dietary assessments. We found no significant difference in energy intake after 4.3years between the groups (metformin vs placebo: -31.0kcal/d; 95% CI, -107.4 to 45.4; F-value, 1.3; df=415; P=.27). Body weight in placebo users increased significantly more than in metformin-users during 4.3years (4.9 +/- 4.9 vs 1.1 +/- 5.2kg; t test: P.001). Linear mixed models did not show a significant effect of energy intake as explanation for the difference in weight gain between the groups (F-value, 0.1; df=1; P=.82). In conclusion, the prevention of weight gain by metformin cannot be explained by reduced energy intake.