Effects of repeated cycles of fasting-refeeding on brown adipose tissue composition in mice.

Mice fasted for 24 h showed reductions in carcass fat and gonadal fat depots and atrophy of brown adipose tissue (BAT) that was characterized by loss of protein and succinate dehydrogenase. These changes were reversed on 24 h of refeeding. Cycling mice experienced 14 cycles of 1 day of fast followed by 2 days of refeeding, whereas control mice were fed ad libitum. Weight loss during each fast remained constant, and the animals lost and regained in excess of twice their initial weights within 6 wk. However, final weight and carcass and gonadal fat weights were similar to those of animals fed ad libitum. Total food intake was similar between cycling mice and those fed ad libitum suggesting an increase in feeding efficiency. There was no development of resistance to food deprivation since the preceding fasting experience of the animal had no effect on weight and carcass fat loss during a 24- or 48-h fast. Norepinephrine-stimulated oxygen consumption that was reduced in cycling mice was probably the result of a reduction of BAT thermogenic capacity. BAT succinate dehydrogenase content and the concentration of uncoupling protein in isolated mitochondria were significantly reduced. These changes in BAT composition were not observed when the refeeding period of each cycle was increased to 6 days. These results suggest that reduced energy expenditure in BAT may play a role in the conservation of energy during intermittent and frequent bouts of food deprivation.