Compared with pharmaceutical research, studies evaluating diet or dietary interventions for chronic diseases like obesity (to be distinguished from micronutrient deficiency syndromes like scurvy or rickets) have far greater challenges in terms of consistency, quality control, confounding, and interpretation. For instance, a placebo for an active drug can be easily prepared, but dietary assignment can rarely be truly masked. Moreover, diet is highly heterogeneous, with myriad interacting and potentially confounding factors. If an intervention increases intake from one food category, participants may well eat less from other food categories.