Learned control of meal size in spontaneously obese and nonobese bonnet macaque monkeys

Ten pairs of obese and nonobese monkeys, matched for age and sex, received one liquid test meal a day for 4 days. Testing was conducted during the middle of a 6-h period of food deprivation. At all other times the monkeys were freely fed on maintenance chow biscuits. The first test meal of grape and orange flavor drinks familiarized them with fluids containing an intermediate level of added carbohydrate (CHO) (27.5%); equal volumes of grape and orange flavors were presented. During testing, the positions of the two flavors were switched three times, thus forcing the monkey to make four choices during the meal. On days 2 and 3, four pairs of monkeys received low-energy liquid meals (10% CHO), and six pairs received high-energy meals (45% CHO); half of the pairs in each group had orange flavor, half grape. On day 2, meal volumes did not differ between the 10% and 45% CHO groups; rather, the size of the meal (regardless of CHO composition) correlated with mean daily chow intake. On day 3, the volume consumed of the 10% CHO solution increased and the volume of the 45% CHO solution decreased, generating a difference between groups that indicated one-trial learning of control of meal size. On day 4, each monkey was given a test meal of repeated choices between samples of grape and orange flavor, both containing the intermediate 27.5% CHO.(ABSTRACT TRUNCATED AT 250 WORDS)