Description and evaluation of an experimental model to examine changes in selection between high-protein, high-carbohydrate and high-fat foods in humans

Objective: To develop and test an experimental model designed to detect changes in selection between foods individually enriched in protein, carbohydrate and fat in human subjects. Design: Randomised counterbalanced (Latin square) design. Setting: The metabolic suite at the Rowett Research Institute's Human Nutrition Unit. Subjects: 16 normal-weight men (mean BMI = 23.5). Interventions: Subjects were each studied 4 times in a 2-day protocol. On day 1 subjects received a fixed maintenance diet; on day 2 they received a mandatory intake as breakfast (08.30) plus a drink at 10.30. This comprised 80% of resting energy requirements as high-protein (HP), high-carbohydrate (HC) or high-fat (HF) foods (60% of energy in each case) or an equal mixture (M) of macronutrients, 33% by energy. All mandatory treatments contained the same energy content and density. From 12.30 onwards, subjects had nd libitum access to a counter-balanced selection of three groups of familiar foods ( 10 HP, 10 HC and 10 HP; 30 foods in total). Most energy in each food was derived from one macronutrient (similar to 60%), the remainder being equally split between the other two macronutrients. Results: Subjects were significantly less hungry before lunch on the HP and M (33% protein) treatments (F-3.44 = 7.35; P < 0.001). At lunch, they ate more energy after the HF treatment than after any of the other treatment (F-1,(38) = 9.00; P = 0.005). This was largely in the form of fat and protein, and to a lesser extent carbohydrate. Subsequent energy intake (EI) were lower on the HF treatment, largely through selection of less fat in the afternoon (F-1,F-42 = 6.90; P = 0.012). Daily EIs were similar across treatments. Conclusion: This design appears sensitive meal-to-meal to changes in both nutrient and EIs.