The impact of the covert manipulation of macronutrient intake on energy intake and the variability in daily food intake in nonobese men

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To investigate the effect of macronutrient composition on ad libitum food intake in nonobese men.


Balanced, incomplete-block, crossover study where subjects received two of three treatments. Macronutrient composition was manipulated by providing 2.1 MJ/day high-carbohydrate (CHO), high-fat (FAT), and/or high-protein (PRO) drinks every day over the course of two, 8-week periods.


In all, 12 healthy normal weight men (age: 39±9 years, BMI: 24.1±1.4 kg/m2).


Ad libitum food intake was measured continuously for 16 weeks at the Beltsville Human Nutrition Research Center (BHNRC). Body composition (DEXA) and body weight were also measured.


Average energy intake (EI) during weeks 1 and 2 was lower for CHO than FAT (P<0.05), but this effect disappeared by week 3. EI during CHO increased by 11% from week 1 to 8 through the increased selection of carbohydrate and protein-containing foods, but not fat foods. Food intake was variable, both between and within subjects, but was not related to macronutrient composition.


EI appears to be influenced by macronutrient composition in the short-term when diets are modified, but the effect dissipates in a few weeks if the diet is maintained. These data suggest the presence of macronutrient-specific regulatory mechanisms in the body, but do not support the notion that a high intake of any of the three macronutrients suppresses EI over a prolonged period of time. The high variability in food intake does not appear to be related to macronutrient composition.

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