Relationship between overnight energy expenditure and BMR measured in a room-sized calorimeter

OBJECTIVE: The purpose of this study was to determine if overnight energy expenditure, the lowest energy expenditure sustained for 60 min during the night, measured and predicted basal metabolic rate are equivalent. DESIGN: Overnight energy expenditure (ON-EE), the lowest energy expenditure sustained for 60 min during sleep (LS-EE) and basal metabolic rate (BMR) were measured two to seven times in a room-sized indirect calorimeter in 69 adult subjects. Subjects' gender, age, weight and height were also used to predict BMR (FAO/WHO/UNU, 1985) (BMR-WHO). SETTING: Beltsville Human Nutrition Research Center, Beltsville, MD, USA. RESULTS: The results from calorimetry measurements (mean +/- s.d.) included: ON-EE (6.87 +/- 0.99 MJ/d), LS-EE (6.18 +/- 0.94 MJ/d) and BMR (6.87 +/- 0.99 MJ/d). Predicted BMR mean was: BMR-WHO, 6.95 +/- 1.03. The mean within-subject difference for the calorimetry measurements were: ON-EE, 0.21 MJ/d; LS-EE, 0.16 MJ/d; and BMR, 0.34 MJ/d. Results indicate there was no significant difference between ON-EE, BMR and BMR-WHO. LS-EE was significantly lower (P < 0.0001) than ON-EE, BMR and BMR-WHO. CONCLUSION: These results indicate that while metabolic rate drops significantly below BMR during sleep, overnight metabolic rate and BMR are equivalent.