Meal-to-meal and day-to-day macronutrient variation in an ad libitum vending food paradigm

Background Theory posits that macronutrient intake is regulated by protein consumption and adequate intake of protein results in consumption of less carbohydrates and fat. The current study investigates the effect of protein intake on calorie and macronutrient content using an ad libitum vending machine paradigm. Methods Healthy volunteers (n = 287; 177m; Age = 36 ± 11; BMI = 32 ± 8) were admitted to our clinical research unit. Macronutrient meal content (grams) and energy intake (Kcal) were quantified by specialized food processing software and collected on an hourly basis over a three-day period using a validated ad libitum vending machine paradigm. Body composition was assessed by DXA. Lagged multi-level models accounting for age, sex, race/ethnicity, fat and fat free mass indices were fitted to examine the impact of prior macronutrient content on subsequent meals. Results Protein intake was associated with decreased energy intake (Kcal; B = −1.67 kcal, p = 0.0048), lower protein and carbohydrate intake (B = −0.08 grams, p = 0.0006; B = −0.21 grams, p = 0.0003, respectively) at subsequent meals. Daily Macronutrient intake and subsequent intake were positively associated. Conclusions Dietary protein exhibits a negative regulatory effect on a short-term meal-to-meal rather than day-to-day basis. In the setting of readily available food, protein intake impacts energy intake only over very short time courses.