Age-related changes in rat adipose tissue cellularity are altered by dietary restriction and exercise

This study examined the effects of diet restriction and exercise training during aging on adipocyte size and number in male Wistar rats. An average of 30 weanling rats each were assigned to one of four experimental groups: ad libitum access to food, nonexercised; diet restricted, nonexercised; ad libitum access to food, exercised; diet restricted, exercised. Diet-restricted groups were allowed free access to food every other day, and, over the course of the study, they consumed 18-25% less than the groups allowed ad libitum access. Exercise training consisted of swimming on alternate days for up to 3 h per exercise period. Fat cell size, number and fat depot mass were determined in the inguinal, epididymal and perirenal fat depots at 12 mo of age and every 4 mo thereafter until 28 mo of age. Fat cell number was not influenced by age, exercise or food restriction in the epididymal or perirenal fat depots. Inguinal cell number was lower (P < 0.05) in the diet-restricted, exercised group at all ages compared with all other treatments. Dietary restriction and exercise training significantly decreased fat depot mass and fat cell size, with dietary restriction having the greatest effect. A bimodal distribution of adipocytes was observed in the epididymal, perirenal and inguinal depots of animals allowed ad libitum access to food. The presence of a large population of small fat cells (< 35 microns) indicated that even in the very aged animal there was the propensity for large variations in fat pad mass. The influence of diet restriction, exercise and aging on adipocyte cell size was highly variable and these effects were dependent on adipose tissue depot location.