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 ad libitum access to a counter-balanced selection of three groups of familiar foods (10 HP, 10 HC and 10 HF; 30 foods in total). Most energy in each food was derived from one macronutrient (approximately 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 (F3.44 = 7.35; P < 0.001). At lunch, they ate more energy after the HF treatment than after any of the other treatment (F1,38 = 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 (F1.42 = 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.