Human dietary responses to covert manipulations of energy, fat, and carbohydrate in a midday meal.

Dietary responses to dilution or supplementation of the energy value and macronutrient content of foods are poorly characterized in humans. After a 1-wk baseline, 16 free-living, normal-weight adults were provided midday meals systematically varying in energy, fat, and carbohydrate contents for 5-d periods. Their compensatory free-feeding intake was monitored through diet records. In response to energy dilution by carbohydrate or fat, mean daily energy intake was 88% and 97% of baseline, respectively. Responses to the energy surfeit led to intakes 104% and 116% of baseline, respectively. However, the absolute magnitude of the carbohydrate supplement challenge was small. Adjustments of macronutrient-specific intake during the high-carbohydrate, low-carbohydrate, high-fat, and low-fat meal periods were 134%, 91%, 165%, and 95% of baseline, respectively. Although these group findings indicate that defense against covert dilution of the energy, fat, or carbohydrate contents of a meal is stronger than that to supplementation, individual responses were highly variable.