Why do mice over-eat high fat diets? How high fat diet alters the regulation of daily caloric intake in mice

OBJECTIVE: Ad libitum high fat diet (HFD) spontaneously increases caloric intake in rodents, which correlates positively with weight gain. However, it remains unclear why rodents overeat HFD. We investigated how changing the proportion of diet that came from HFD might alter daily caloric intake in mice. METHODS: Mice were given 25%, 50%, or 90% of their daily caloric need from HFD, along with ad libitum access to a low-fat rodent chow diet. Food intake was measured daily to determine how these HFD supplements impacted total daily caloric intake. Follow up experiments addressed timing of HFD feeding. RESULTS: HFD supplements did not alter total caloric intake or body weight. In a follow up experiment, mice consumed ~50% of their daily caloric need from HFD in 30 minutes during the light cycle, a time when mice do not normally consume food. CONCLUSIONS: HFD did not disrupt regulation of total daily caloric intake, even when up to 90% of total calories came from HFD. However, HFD increased daily caloric intake when provided ad libitum, and was readily consumed by mice outside of their normal feeding cycle. Ad libitum HFD appears to induce overconsumption beyond the mechanisms that regulate daily caloric intake.