Dose Response Effect of a Whey Protein on Appetite Profile, Energy Metabolism and Intake

PURPOSE: To determine the effects of high (HWP) and low whey protein (LWP) at breakfast[TM1] on appetite profile, thirst, energy metabolism and subsequent energy intake. METHODS: Seventeen healthy participants (age 27 ± 7 y, BF 21.5 ± 6.9%, BMR 1741 ± 391 kcals/day) consumed one of three smoothies at breakfast on three separate days in randomized order. The energy intake from smoothies consisted of control (10% fat and 90% carbohydrate), LWP (20% whey protein, 10% fat and 70% carbohydrate) and HWP (40% whey protein, 10% fat and 50% carbohydrate), followed by an ad libitum lunch 3 hours later. Appetite profile was completed using a visual analog scale (VAS) before, at 0, 60, 120, and 180 minutes. Resting metabolic rate (RMR) 30 minutes before and thermic effect of a meal (TEM) at 45-60, 105-120, and 165-180 minutes were measured by indirect calorimetry to determine oxygen consumption (VO2) and respiratory quotient (RQ). The accepted level of significance was set at p < 0.05. RESULTS: Energy intake at lunch was higher (p = 0.02) following control (770 ± 289 kcals) compared to HWP (654 ± 252 kcals) and LWP (671 ± 217 kcals). Participants hunger, desire to eat, and perceived amount were significantly higher, whereas, satiety and fullness were lower after control compared to HWP and LWP. A significant difference over time was observed in thirst and cravings of sweet, salty savory and fatty, however there were no significant condition by time interactions. Additionally, a lower RQ (p < 0.001) and higher VO2 (p < 0.001) was observed for HWP (4.3 ± 0.6, 4.2 ± 0.5, and 4.0 ± 0.5 ml · kg-1· min-1) compared to LWP (4.1 ± 0.6, 3.9 ± 0.5, and 3.5 ± 0.5 ml · kg-1· min-1) and control (4.0 ± 0.6, 3.7 ± 0.5, and 3.5 ± 0.4 ml · kg-1· min-1) at 45-60, 105-120, and 165-180 minutes, respectively. CONCLUSION: Breakfast with HWP and LWP were rated as more satiating coinciding with reduced subsequent energy intake at lunch. In addition, these results suggest a dose-response effect of whey protein on energy metabolism over 3 hours following breakfast.