Probing the causes of high-fat diet hyperphagia: a mechanistic and behavioral dissection

High-fat diets promote hyperphagia in both rats and humans; however, understanding of the process by which dietary fat increases intake is incomplete. Since altering the fat content of a diet simultaneously changes both its sensory properties and postingestive effects, it is unclear whether high-fat diet hyperphagia is driven by oral influences, postingestive factors, or both. Previous findings from both animal and human studies indicate that relatively "less palatable" high-fat diets are overeaten relative to high-carbohydrate diets, indicating that the postingestive effects of high-fat foods are sufficient to promote hyperphagia. A program of research on rats is described, which isolates and assesses the independent effects of sensory and postingestive influences on intake of liquid high-fat and high-carbohydrate diets. An integrated series of experiments investigates both short-term (meal size, postprandial satiety) and long-term (ad lib intake over weeks) effects of diet composition on intake in order to "dissect" the causes of high-fat diet hyperphagia. Preliminary findings from this approach indicate that the postingestive effects of a high-fat diet promote longer meal size, less postprandial satiety per calorie, and greater daily calorie intake than a high-carbohydrate diet.