Long term control of food intake in the monkey

Deceleration in cumulative food intake curves, changes in body temperature and diet-induced thermogenesis

In order to assess the relationship between the shape of the cumulative food intake curve and a reflection of internal processes, eating behaviour, postprandial thermogenesis, and skin and core temperature of normal weight restrained and unrestrained eating women and of obese restrained eating women were recorded during four-course solid food lunches, eaten in a laboratory setting (respiration chamber) at a constant ambient temperature of 22 degrees C. The skin temperature (upper arm, upper leg, liver proximity) and core temperature were measured constantly from one hour prior to until two hours after the lunch. Normal weight unrestrained eaters displayed decelerated cumulative food intake curves and an increase in the liver temperature data of 0.8-1.5 degrees C, from the beginning of the meal onwards, remaining high until 60-90 minutes after the meal was consumed. The postprandial thermogenesis of normal weight unrestrained eaters was on average 8.1 +/- 1.3%, calculated over two and a half hours from the beginning of the meal. Overweight and normal weight restrained eaters displayed linear cumulative food intake curves, almost no changes in skin and core temperatures and a postprandial thermogenesis of 4.2 +/- 0.3% and 4.8 +/- 0.7%, calculated over two and a half hours from the beginning of the meal onwards. In conclusion, deceleration in cumulative food intake curves is positively correlated with a temperature increase in the skin in the proximity of the liver, and with postprandial thermogenesis.

Interdependency of food and water intake in humans

The temporal and quantitative relationship between food and water intake and the effect of fluid restriction on voluntary food intake were studied in 20 male subjects over two 48-h periods. Food intake was limited to specific mealtimes, but subjects could eat as much as they wanted during these times. Drinking was ad libitum in one condition, and limited by about 40% of ad libitum drinking in the other condition. Approximately 68% of all drinking occurred when food was available at mealtimes when drinking was ad libitum. When fluid intake was limited, subjects voluntarily reduced their food intake. Food acceptability, as measured by hedonic ratings, was not significantly affected by fluid restriction even though food intake was significantly reduced. The intensity rating of thirst was negatively correlated with food intake. Indirect comparisons are drawn with eating and drinking relationships in non-human species.

Characteristics of spontaneous obesity in male rhesus monkeys

Adult male rhesus monkeys representing a wide range of adiposity were characterized according to body dimensions, eating behaviors, and endocrinologic/metabolic indices. Body fat, located most prominently on the abdomen, ranged from 30 to 61% of body weight. Three groups were formed on the basis of body composition data: Very Obese (VO), Moderately Obese (MO) and Nonobese (N). These groups did not differ in food intake, preferences for sweet solutions, or compensatory changes in food intake following consumption of sugar solutions. Glucose tolerance was normal, but fasting insulin levels and insulin response to glucose loading increased with increasing adiposity. Fasting triglyceride levels were highly correlated with insulin values and body fat. It is concluded that some adult male rhesus monkeys develop obesity without obvious differences in eating behavior and that obese monkeys, like obese humans, are at risk for diabetes mellitus and its complications.

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.