The effects of whey and soy liquid breakfast on appetite response, energy metabolism, and subsequent energy intake.

OBJECTIVES: The aim of this study was to examine the effects of animal-based protein (whey; WP) compared with plant-based protein (soy; SP) and carbohydrate (CHO) liquid breakfast on appetite, energy metabolism, and subsequent energy intake.

METHODS: Seventeen healthy individuals consumed three isocaloric breakfast smoothies with whey, soy, or carbohydrate (no protein) in a double-blind, randomized crossover design. Participants completed an 11-point rating scale of appetite profile (before, 0, 60, 120, and 180 min). Indirect calorimetry was used to determine the thermic effect of a meal (TEM; at 45-60, 105-120, and 165-180 min). An ad libitum lunch was offered at 180 min after breakfast and energy intake was assessed.

RESULTS: There was a significant difference in hunger (P = 0.033), fullness (P = 0.002), satiety (P = 0.001), desire to eat (P = 0.024), and prospective food consumption (P = 0.021) between the three breakfast meals. Fullness and SP compared with CHO. A higher (P < 0.001) TEM and lower (P < 0.05) respiratory exchange ratio (RER) was observed after WP and SP compared with CHO. In addition, a higher (P = 0.022) energy intake at lunch was observed after CHO (769 ± 259 kcal) compared with WP (654 ± 252 kcal) and SP (664 ± 296 kcal), with no difference (P = 0.966) between WP and SP. Consuming SP at breakfast exerts comparable effects to WP on appetite profile, energy metabolism, and subsequent energy intake, suggesting that SP is a reasonable alternative to WP as a protein supplement source to aid in body weight control.