A secondary analysis of a randomized clinical trial found that adopting a vegan diet significantly reduced dietary energy density (calories per gram of food). Energy density for each participant was calculated as the division of the total daily energy intake (kcal/day) on the total food weight (g/day). For the association of change in energy density with body weight loss, repeated measures analysis of variance and linear regression were used. One kg of body weight loss correlated with 0.29 decrease in energy density (P < .001) which became 0.36 decrease after adjusting for energy intake (P = .002). This is consistent with a relationship between a low energy density diet and body mass loss.