Effects of early overnutrition and undernutrition in rats on the metabolic responses to overnutrition in later life.

Weanling rats fed a palatable "cafeteria" diet consumed 40-70% more energy than stock fed controls but also showed a marked (80%) increase in energy expenditure (diet-induced thermogenesis) so that body weight and body energy gain were almost identical in both groups. Animals previously fed the cafeteria diet for 30 days after weaning exhibited lower weight gains when re-exposed to the cafeteria diet at 90 days of age than either naive rats or rats which had been fed the cafeteria diet continuously from weaning. Rats which had been undernourished for 30 days form weaning and allowed to recover for 30 days showed similar responses to the cafeteria diet as normal animals. Hypertrophy of brown adipose tissue (BAT) was seen in all cafeteria fed rats but hyperplasia (increased DNA content) was observed only in rats which had been overfed in early life. These results suggest that overfeeding young, weanling rats can result in a lower fat content, a greater thermogenic capacity and resistance to obesity later in life and may be due to a permanent increase in BAT cell number.