Human Resting Energy Expenditure Varies with Circadian Phase.
Level 4 - case-series / case-control
Small prospective physiological laboratory study (case series / within-subject protocol)
PubMed 30416064 · doi:10.1016/j.cub.2018.10.005
What was done
Seven participants completed a forced desynchrony protocol designed to uncouple endogenous circadian rhythms from behavioral cycles (sleep-wake, physical activity, and feeding). Fasted resting energy expenditure (REE) and respiratory quotient (RQ) were measured across different circadian phases and mapped against the endogenous core body temperature nadir.
What was found
The abstract does not provide absolute energy expenditure values, percentages, or effect sizes, but reports directional phase relationships. Fasted REE varied by circadian phase, reaching a minimum at circadian phase ~0° (corresponding to core body temperature nadir in the late biological night) and a maximum at ~180° (biological afternoon and evening). Fasted RQ (macronutrient utilization) was lowest at phase ~240° and highest at ~60° (biological morning).
Why it matters
This study provides evidence that human resting metabolic rate and substrate utilization have an endogenous circadian rhythm independent of diet, sleep, and activity. This rhythm may help explain metabolic disruption and weight gain observed in shift workers.
Limits
The sample size is very small (n = 7), and the abstract provides no demographic details (such as age, sex, or metabolic health) or numerical measurements of effect magnitude. The controlled forced desynchrony environment isolates endogenous rhythms but does not capture real-world behavioral interactions.
Cited by
- context In order to wake up feeling refreshed and energized, core body temperature must increase by approximately 1 to 3 degrees Fahrenheit.