The Effect of Pre Sleep Casein Protein Consumption on Next Morning Resting Metabolic Rate in Resistance Trained Women

Abstract

Nighttime eating has been discouraged by the media due to its purported negative implications on metabolism. However, recent studies have shown that nighttime casein protein (PRO) either increases or has no effect on next morning resting metabolic rate (RMR). However, the effects of eating PRO at night on RMR in resistance-trained women is unclear. PURPOSE: To examine the effect of consuming nighttime PRO on next-morning RMR in resistance-trained women. METHODS: Thirteen healthy, resistance- trained (squat 100% body weight, bench press 70% body weight), normal weight and fatness (BMI, 19.9±2.3 kg/m2; body fat 28.7±4.9%), eumenorrheic females (age, 22±3 years) volunteered for this study. Participants reported to the lab on four different occasions: pre-testing and maximal testing familiarization (1a), maximal testing (1b), and two experimental trials (2 and 3). Thirty minutes before bed participants consumed micellar casein protein (PRO; 30g protein, 120kcals) or a non-caloric, sensory-matched placebo (PLA; 0g protein, 0kcals) in random order. RMR and respiratory exchange ratio (RER) were measured using open-circuit indirect calorimetry at baseline (BL) and immediately upon waking (AM) the following morning. RESULTS: There was no significant change in next-morning RMR when consuming PLA (BL: 1554±193; NM: 1537±204 kcal/d; Δ= -17kcal/day; p=0.41), or PRO before bed (BL: 1551±156; NM: 1525±171 kcal/d; Δ=-26 kcal/day; p=0.36). There was no significant change in next-morning RER when consuming PLA (BL: 0.74±0.05 CO2/O2; NM: 0.76±0.04 CO2/O2; Δ=0.02 CO2/O2; p=0.13) or PRO before bed (BL: 0.77±0.05; NM: 0.77±0.02; Δ=0.0; p=0.29). CONCLUSIONS: In resistance-trained women, 30g of casein PRO pre-sleep does not significantly change next morning RMR or RER. Therefore, it is metabolically feasible for women to consume protein at night without negative metabolic implications. This study was supported by Dymatize® Nutrition and FrieslandCampina®.