Diet composition alters the acceptance of fat by rats

The acceptance of dietary fat by rats is influenced by changes in fat digestion and metabolism. In these experiments, rats were fed diets that differed in fat, carbohydrate and fiber content, and the acceptance of fat was measured. Rats fed a high fat (HF) diet ate more corn oil in 30-min or 6-h tests than did rats fed an isocaloric high carbohydrate (HC) diet. This effect was seen after the diets were switched and rats retested. Differences in dietary fiber between the isocaloric HF and HC diets did not account for this effect because rats fed HF diets, either high or low in fiber content, drank more oil than rats fed the HC diet. Rats fed the HF diet with added carbohydrate drank less oil than rats fed the HF diet, and the same amount of oil as rats fed the HC diet. Compared with rats fed the HC diet, rats fed the HF diet drank more oil in a two-bottle preference test with sucrose or when mixed with sucrose in a single-bottle test. Rats offered a variety of fats, sugars or other test foods, ate more nutritive liquid fats and some solid fats, but did not eat more sugar or other items if they were fed the HF diet rather than the HC diet. These studies taken together strongly suggest that rats fed a high fat diet show a greater acceptance of fat compared with rats fed a high carbohydrate diet.