Feeding behavior during experimentally induced obesity in monkeys.

In order to investigate the effects of the induction and remission of obesity on feeding behavior, male rhesus monkeys were made obese by sustained intragastric (IG) feeding of a complete liquid diet. Intragastric diet infusion levels of 100, 125, 145, and 165% of the baseline oral intake of each monkey were successively administered. During the initial overfeeding period (100% of the baseline oral intake), at least one week was required to reduce voluntary oral intake to less than 25% of the baseline levels and complete suppression of oral intake did not occur. This increased total caloric intake (IG infusion plus oral intake) resulted in a rapid rate of weight gain of at least 5 times the baseline rate. With successive increases in caloric infusion level, oral intake was eventually suppressed, and rapid weight gain was sustained. When the IG infusion was abruptly terminated after 50 to 130 days, 3 monkeys refused all food for 14 to 35 days. The monkeys' oral intakes stabilized three to ten weeks after the end of the overfeeding period. The length of this period prior to the resumption of normal oral intake was not related to length of overfeeding nor to the amount of weight gained. The monkeys' body weights dropped rapidly in the initial post-overfeeding period and then stabilized, sometimes at levels higher than their baseline body weights. In 2 monkeys, at the end of overfeeding the amounts infused were gradually reduced in order to determine the calories required to maintain their body weights at peak levels. Significantly fewer kcal/kg were required to maintain peak body weights than were ingested during the baseline periods.