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Circadian misalignment may explain weight gain among nightshift workers
A reduced total daily energy expenditure seen in nightshift workers, combined with a similar inhibition in response to eating dinner at off hours, could explain the high risk for weight gain in this population, according to research published in the Proceedings of the National Academy of Sciences.
“Healthy individuals placed in a nightshift work schedule and consuming the majority of their meals at night have a lower daily energy expenditure than when they are awake and consuming the same meals during the day,” Andrew W. McHill, PhD, of the University of Colorado, Boulder, told Endocrine Today. “This decrease in energy expenditure may represent a contributing mechanism for weight gain when being awake and eating at night.”
Andrew W. McHill
McHill and colleagues studied 14 healthy adults (eight women; aged 26.4 ± 1.2 years) for 6 days of simulated shiftwork to determine how circadian misalignment may affect metabolic dysregulation.
Participants had a BMI of 22.7 ± 0.5 kg/m2, with 27.4 ± 2.2% body fat as determined by DXA. The investigators quantified changes in energy expenditure, macronutrient utilization, appetitive hormones, sleep and circadian phase during dayshift vs. nightshift work.
Total daily energy expenditure increased by approximately 4% on the transition day to the first nightshift, consisting of an afternoon nap and extended wakefulness. Total daily energy expenditure decreased by approximately 3% on both the second and third nightshift days, consisting of daytime sleep, an afternoon and nighttime wakefulness. An approximate 12% to 16% drop in energy expenditure was seen during scheduled daytime sleep opportunities, despite sleep disturbances.
The amount of energy expenditure above the resting metabolic rate also was reduced in response to a late dinner on the first nightshift. Total daily fat utilization rose on the first and second nightshift days, and carbohydrate and protein utilization dropped on the second nightshift day.
“Our findings of lower energy expenditure when working a nightshift schedule would contribute to weight gain over time if food intake was not reduced or physical activity was not increased,” McHill said.
Hunger ratings waned during nightshift days, despite decreases in 24-hour levels of satiety hormones leptin and peptide YY.
Clinically translatable research is needed to further elucidate the mechanisms for weight gain in shift workers, McHill noted.
“Why energy expenditure was lower during daytime sleep in our study is not clear and requires further research,” he said. “Other potential areas of future research include studying individuals working different shift schedules, with access to ad libitum food and activity. Varying levels of weight and/or body composition also are needed.” – by Allegra Tiver
For more information:
Andrew W. McHill, PhD, can be reached at the Division of Sleep and Circadian Disorders
221 Longwood Ave., Suite 438, Boston, MA 02115; email: andrew.mchill@colorado.edu.
Disclosure: The researchers report no relevant financial disclosures.