The effect on spontaneous food intake of concealed variations in nutritive density of machine-dispensed liquid diet was studied in 5 lean and 4 obese young adults and two obese juvenile subjects. They were unaware of the changes in caloric concentration and that food intake was being monitored.
The lean subjects maintained weight during machine feeding, and when nutritive density was altered, promptly adjusted the volume consumed to maintain near constant energy intake. The obese adults ingested a small fraction of the calories needed to maintain weight and failed to adapt volume intake to appreciable changes in caloric concentration. The obese juvenile subjects consumed large quantities of formula however, one also failed to adjust volume intake when caloric density was varied.
Lean young adults appear to regulate energy intake at the physiologic level when the nutritive concentration of the diet is altered covertly. Grossly obese adults seem incapable of such regulation.
