Resting energy expenditure and substrate oxidation do not differ between night and day shift workers: A real-life...

This cross-sectional study investigated differences in resting energy expenditure (REE), respiratory quotient (RQ), and substrate utilization between night and day shift workers. A total of 62 male workers (30-night shift, 32 d shifts), aged 21 to 62 y, were assessed for anthropometric measurements, sleep parameters, social jetlag, and daytime sleepiness. Indirect calorimetry was used to evaluate REE, RQ, and carbohydrate and fat oxidation. Linear regression models and Generalized Estimating Equations (GEE) were applied, adjusting for potential confounders. Night shift workers exhibited lower RQ and carbohydrate oxidation and higher fat oxidation compared to day shift workers after adjusting for age. However, after further adjustment for workload, no significant differences in REE were observed (night: 1843.31 [1737.21-1931.42] kcal/day; day: 1732.74 [1639.58-1825.91] kcal/day, p = 0.133), RQ (night: 0.88 [0.86-0.91]; day: 0.90 [0.88-0.93], p = 0.331), or substrate oxidation rates - carbohydrate oxidation (g/min: night: 0.20 [0.18-0.23]; day: 0.21 [0.19-0.24], p = 0.583) and fat oxidation (g/min: night: 0.04 [0.03-0.06]; day: 0.03 [0.02-0.04], p = 0.134) - between night and day shift workers. Night shift work does not differ from day shift work in terms of REE and substrate oxidation. Further longitudinal studies with larger samples are needed to confirm these findings.