Compensation for caloric dilution in humans given unrestricted access to food in a residential laboratory

Six adult male research volunteers, in two groups of three subjects each, lived continuously in a residential laboratory for 14 days. All contact with the experimenters was through a networked computer system and subjects' behaviors, including food intake, were continuously recorded. During the first part of the day, subjects remained in their private rooms doing work activities. During the remainder of the day, they had the option to socialize with each other. A wide variety of food items were continuously available. Subjects were in complete control of their pattern of food intake and could consume any item, or number of items, at any time during the day. On days 6 through 11, reduced calorie versions of approximately one third of the food items were covertly substituted for the regular caloric content items. This manipulation decreased intake from the reduced-calorie group of foods by 500 kcal. The subjects immediately and completely compensated for the loss of calories by increasing the number of non-calorie-manipulated food items consumed. When regular calorie foods were again available during the last 3 days of the experiment, subjects failed to compensate for this increase in caloric intake. Thus, under conditions of unlimited access to food, human volunteers completely compensated for caloric dilution, but were less accurate in responding to increases in caloric intake.