Effect of Nighttime Consumption of Protein or Placebo on Morning Measures of Resting Metabolic Rate and Appetite in Pre- and Postmenopausal Women

PURPOSE: To determine the acute effects of nighttime pre-sleep consumption of casein protein and a placebo supplement on morning measures of RMR and appetite in pre- and postmenopausal women. METHODS: This study was a randomized crossover double-blind placebo-controlled trial. Fourteen pre- (n=7, age: 20 ± 2 years) and postmenopausal (n=7, age: 56 ± 5 years) women participated this study. On visit one subjects arrived to the laboratory between 8:00am and 12:00pm. Measurements of anthropometrics, body composition (DXA) and familiarization with RMR measurement were conducted. Visits two and three were used to assess the responses of appetite and RMR to nighttime pre-sleep consumption of a casein protein (35 g, 130 kcals) or placebo supplement 7.2g, 10 kcals). On both visits subjects arrived to the laboratory between 6:00am and 9:00am. Subjects completed a visual analogue scale (VAS) to assess hunger, satiety and desire to eat. This was followed by measurement of RMR via indirect calorimetry. After the completion of visit two subjects returned for visit three and the protocol was repeated. Dependent variables were analyzed by one-way analysis of variance (ANOVA) to determine differences between pre- and postmenopausal women. RMR and measures of hunger, desire to eat, and satiety was analyzed using 2x2 ANOVA (menopause status by supplement). Significance was accepted at p≤0.05 and data were reported as means ± standard deviations. RESULTS: There were no differences in subject characteristic of body composition and caloric intake between pre- and postmenopausal women except for age (pre:20 ± 2; post: 56 ± 5 yrs, p=0.001). There were significant group (pre- vs. postmenopausal) by supplement (casein protein vs. placebo) interactions for RMR expressed as total calories per day [F(1,12)=14.474, p=0.003, effect size (ES)=0.547] and oxygen consumption (VO2) (F(1,12)=7.633, p=0.017, ES=0.389). After consuming casein protein, total caloric expenditure (placebo: 1426 ± 260; casein protein: 1304 ± 269 kcals/day) and relative VO2 (placebo: 3.46 ± 0.40; casein protein: 3.14 ± 0.28 ml/kg/min) were significantly lower in premenopausal women. There were no effects of the supplements in postmenopausal women. No group by supplement interactions or main effects were found on measures of appetite. CONCLUSION: Casein protein did not benefit RMR and appetite in pre- and postmenopausal women. In premenopausal women RMR was lower after consumption of casein protein. This seems unlikely since VO2 measures were extremely high under the placebo condition in premenopausal women. Although casein protein showed no metabolic or appetite effects it is conceivable that an increase of protein in the diet could lead to other advantageous health outcomes over time. Overall the findings support the growing evidence that snack sized portions (150-200 kcal) are not harmful to metabolism or appetite when consumed before sleep.