We review evidence regarding the influence of dietary fat, fiber, the glycemic index and sugar on energy intake and body weight. Although data from comprehensive long-term studies are lacking, published investigations suggest that the previous focus on lowering dietary fat as a means for promoting negative energy balance has led to an underestimation of the potential role of dietary composition in promoting reductions in energy intake and weight loss. More randomized clinical trials are needed to examine the relative utility of different putative dietary factors in the treatment of obesity.