Effects of aging on food intake and body composition in rats.

Alterations in the ability to adjust energy intake when optional dietary foods are available may contribute to aging-related changes in body composition. Ingestive behavior, however, has not been extensively studied in aging models. The present research used young, middle-aged and old rats to examine food intake under several different schedules of optional fat availability. All rats were provided with continuous access to a nutritionally complete diet throughout the 6-week study. In addition, different subgroups within each age had access to an optional source of vegetable shortening under schedules in which the frequency of access was manipulated: controls (C)-- no shortening access; MWF--2-h shortening access on Monday, Wednesday and Friday; D2--2-h shortening access every day; D24--24-h shortening access every day. Energy intake was significantly greater in groups with more frequent access to shortening regardless of age. The length of time the rats remained hyperphagic, however, increased with age. Body weight increased significantly in the D24 group in middle-aged and old rats, but not in young rats. Total body fat was also significantly higher in middle-aged and old groups with more frequent access to shortening, but not in young rats. Finally, body ash mass was significantly reduced in old rats on the D24 diet. These results suggest that alterations in responses to an optional source of dietary fat may contribute to aging-associated body fat accretion and body mineral loss.