Background: Nighttime eating, particularly before bed, has received considerable media attention in recent years. The common thought was to avoid caloric intake post-dinner and pre-sleep due to worries of weight gain and a negative impact on cardiometabolic health. It appears that minimizing nighttime caloric intake by providing a structured low calorie option with a high satiating value (e.g., greater protien content) may alter the risk for overcomsumption and long-term weight gain. Indeed, recent work from our laboratory and others have demonstrated that low-calorie, nighttime snacking options consisting primarily of protein may be beneficial. To date, no studies have investigated the impact of casein intake before bed on overnight and next morning fat metabolism in obese men. Purpose: To determine if casein protein (CAS) consumed at night before sleep will alter overnight subcutaneous abdominal adipose tissue (SCAAT) lipolysis, and next morning whole-body fat oxidation and appetite in overweight and obese men compared to a non-caloric placebo (PLA). Methods: Twelve overweight and obese men participated in this randomized, cross-over, double-blind and placebo-controlled study. Participants came to the laboratory at baseline and twice during each of the treatment periods with CAS and PLA. Each treatment period consisted of one visit in the evening and another the next morning. Participants consumed CAS or PLA and overnight lipolysis was measured with microdialysis, a minimally invasive method used to monitor SCAAT interstitial glycerol concentrations. The next morning fat oxidation and metabolism (indirect calorimetry), and appetite (visual analog scales for hunger, satiety, and desire to eat) were measured. Results: There were no significant differences in overnight SCAAT interstitial glycerol concentrations (CAS, 175.0 ± 26.5; PLA, 184.8 ± 20.7 μmol/L; p =0.77), fat oxidation (CAS, 0.76 ± 0.01; PLA, 0.76 ± 0.01; p =0.75), metabolic rate (CAS, 2126 ± 111; PLA, 2145 ± 106 kcals/day; p =0.94) or any markers of appetite between CAS and PLA. However, the participants in the present study were hyperinsulinemic (fasting insulin > 30 μUL), which may have masked any potential differences in the dependent variables. Conclusion: Despite common concern for eating at night before bed, it appears that casein protein had no impact on overnight lipolysis or whole-body fat oxidation and therefore does not appear to have any negative effects compared to a non-caloric placebo in obese men. (ClinicalTrials.gov NCT02211391)
