Circadian rhythm influences calorie burning after eating

Han-Chow Koh, PhD, and Frank A.J.L. Scheer, PhD, of the Medical Chronobiology Program at the Division of Sleep and Circadian Medicine in the Mass General Brigham Department of Medicine, are the co-lead and senior author, respectively, of a paper published in Metabolism, "Constant-routine protocol reveals an endogenous circadian rhythm in diet-induced thermogenesis with a peak in the biological morning."

Q: What challenges or unmet needs make this study important?

There is emerging evidence linking eating meals in the later part of the day to greater body weight. Our previous work has supported this premise, showing that when people delay their mealtimes by about four hours, they burn fewer calories across the time they spend awake. However, whether this is due to the influence of our body clock was not clear.

It is also known that diet-induced thermogenesis (DIT)-how much energy the body spends processing and storing nutrients after eating-varies at different times of the day, with higher levels in the morning versus the evening. However, it's been unclear whether this time-of-day difference in DIT is due to behaviors or environmental factors (such as sleep/wake, rest/activity, fasting/eating or dark/light cycles) or to the endogenous circadian system (our 24-hour "body clock").

Q: What central question(s) were you investigating?

Essentially, we wanted to find out whether there's a rhythm in energy expenditure after eating that's dictated, or at least partially dictated, by our body clock. We hypothesized that the discovery of such a rhythm could mechanistically link late eating with increased body weight.

Q: What methods or approach did you use?

In order to determine whether our circadian rhythms influence diet-induced thermogenesis independent of confounding influences like behavioral and environmental factors, we used a gold standard methodology in the field of circadian biology called the Constant Routine protocol.

In this protocol, variations in environmental factors (such as light exposure and indoor temperature) and behavioral factors (such as sleep, posture and physical activity) are removed. This reveals the true impact of underlying endogenous circadian rhythms alone.

Q: What did you find?

The data revealed an independent influence of the human circadian timing system on diet-induced thermogenesis. Our body clock causes diet-induced thermogenesis to peak in the biological morning (around 7 a.m. for our participants) and to reach the lowest values in the biological evening (around 7 p.m.).

Our work is important because it provides evidence to support the theoretical framework that eating primarily towards the morning hours increases daily energy expenditure, while evening-predominated eating decreases daily calories burnt.

By detailing the circadian system's influence on our metabolism, we help explain why late eating may contribute to increased body weight or struggles with weight loss.

Q: What are the real-world implications, particularly for patients?

These findings address a fundamental question in chronobiology (the branch of science that studies how biological processes follow natural timing patterns) and human metabolism. They have important implications for understanding energy balance and body weight regulation, and developing evidence-based meal timing recommendations for metabolic health.