Is energy density a useful concept for understanding and preventing obesity?

Aim: Short-term studies suggest that dietary energy density may be an important factor for understanding and preventing obesity. This review reassesses this concept in the light of recent prospective cohort studies and randomised controlled trials. Methods: A computerised search was conducted of English language papers on Medline. Additional articles were identified by searching references in relevant papers. Results: Six long-term prospective cohort studies do not consistently support an association between dietary energy density and changes in body weight over time. The largest study finds no relation and the results of other studies are mixed. In three randomised controlled trials, advice to follow low energy density diets ad libitum induces modest, short-term weight loss but has minimal effect in the long term. Weight loss trials employing reduced energy, low energy density diets may be effective for losing body weight over 6 months, the degree of weight loss being comparable to that achieved with other reduced energy diets. The pattern of weight change observed in ad libitum feeding studies suggests adaption to a change in energy density with an increase in the weight of food consumed. This challenges the fundamental assumption of the energy density hypothesis that the weight of food consumed each day is a constant and instead suggests that the body tends to prioritise energy intake in the long term. Conclusions: Despite its intuitive appeal, dietary energy density appears to be of limited use for understanding obesity or preventing its development.