Summary: A new controlled study provides clear mechanistic evidence linking late-night eating to weight gain. Researchers show that the body’s internal 24-hour clock—our circadian system—directly regulates diet-induced thermogenesis (DIT), the extra calories burned to digest, absorb, and store a meal. The study demonstrates a pronounced daily rhythm in DIT that peaks in the biological morning and falls to its lowest point in the biological evening, independent of sleep, activity, or light exposure.
Previous observations have shown that human metabolism tends to be more active earlier in the day and slower at night, but it was unclear whether those patterns were caused by behavior (sleep, movement, light) or by an intrinsic biological clock. Using a rigorous laboratory approach that removes environmental and behavioral influences, investigators isolated the endogenous circadian signal and documented a robust timing effect on post-meal energy expenditure.
Key Findings
- Circadian peak: Diet-induced thermogenesis naturally reaches its highest point in the biological morning (approximately 7:00 AM), so the body expends more energy processing the same food early in the day.
- Evening trough: DIT falls to its lowest baseline in the biological evening (around 7:00 PM), meaning identical meals consumed at night require less energy to process and therefore leave more calories available for storage.
- Rigorous protocol: Researchers used the gold-standard Constant Routine protocol to eliminate changing light, posture, sleep, temperature, and activity, allowing measurement of internal circadian effects alone.
- Independent of behavior: The circadian modulation of calorie-burning after meals is driven by the body’s internal clock and occurs regardless of a person’s sleep–wake schedule or physical activity.
- Weight regulation: The endogenous rhythm provides a biological explanation for why delaying mealtimes reduces total waking calorie expenditure and is associated with greater difficulty losing weight.
- Clinical implications: Findings support chronobiology-based recommendations that prioritize larger calorie intake earlier in the day to align meals with peak metabolic processing.
Source: Mass General Brigham
Study team and publication: Sleep and circadian researchers at Mass General Brigham, including Han-Chow Koh, PhD, and Frank A.J.L. Scheer, PhD, led this investigation. The results are published in the journal Metabolism under the title “Constant-routine protocol reveals an endogenous circadian rhythm in diet-induced thermogenesis with a peak in the biological morning.”
Why this matters
Emerging evidence links late eating with higher body weight. Earlier work by this group found that delaying meals by several hours reduces total calories burned while awake. The present study addresses whether such effects are caused by behavioral habits or by an intrinsic circadian rhythm. By isolating internal timing, the investigators confirmed that the circadian system itself controls fluctuations in DIT across the day, offering a direct physiological mechanism that connects meal timing to energy balance and body weight.
Methods in brief
To separate the effects of behavior and environment from the internal clock, researchers used the Constant Routine protocol. Participants remained awake for 36 hours in a controlled setting with dim lighting, a semi-recumbent posture, stable temperature, and evenly spaced identical meals. This approach removes changes in sleep, activity, light, or posture so that remaining patterns reflect endogenous circadian rhythms.
What the study found
Among 16 adults with overweight or obesity who completed the protocol, the team observed a significant circadian rhythm in diet-induced thermogenesis. DIT peaked in the biological morning and reached a trough in the biological evening, with a peak-to-trough amplitude representing a meaningful difference in caloric processing across the day. The rhythm persisted after adjusting for circadian changes in fasting energy expenditure, and it was not altered by prior meal timing schedules in exploratory analyses.
Clinical and practical implications
The core practical takeaway is that meal timing matters: eating more calories earlier in the day aligns food intake with the body’s peak thermogenic capacity, increasing daily energy expenditure from digestion. Conversely, large evening meals are processed at a time when the circadian system reduces thermogenesis, lowering daily calorie burn and potentially promoting weight gain. These results bolster time-of-day strategies for metabolic health and weight management that emphasize earlier, not later, caloric intake.
Authorship and acknowledgments
Lead and senior authors include Han-Chow Koh and Frank A.J.L. Scheer. Additional Mass General Brigham co-authors are Nina Vujović, Su Wei Heng, Priyanka Panjwani, Charlotte Van Zee, Wei Wang, and Jingyi Qian. Marta Garaulet is listed among the other contributing authors.
Funding
This work was supported by the National Institutes of Health (NIH), grant R01DK099512.
Disclosures
Frank Scheer reports consulting or advisory roles with The University of Alabama at Birmingham, Morehouse School of Medicine, and the Salk Institute for Biological Studies. Nina Vujović reports consulting or advisory relationships and employment and equity ties with Novartis organizations.
Key Questions Answered:
A: Diet-induced thermogenesis is the rise in metabolic rate after eating, reflecting the energy cost of digesting, absorbing, transporting, and storing nutrients. Because DIT is a substantial component of daily energy expenditure, its timing influences overall calorie burn. The study shows that DIT is highest in the biological morning and lowest in the biological evening, so identical meals eaten at night demand less energy to process, potentially increasing the risk of storing excess calories as fat.
A: The Constant Routine protocol holds environmental and behavioral conditions constant—continuous dim light, controlled temperature, fixed posture, and regular identical snacks—while keeping participants awake. By removing external fluctuations, any remaining rhythmic changes in metabolism can be attributed to the internal circadian clock rather than to sleep, activity, or light exposure.
A: Consider aligning meal timing with the body’s natural metabolic rhythm by consuming larger meals earlier in the day and avoiding large late-evening meals. Such timing may enhance the energy cost of digestion and support daily energy balance, complementing calorie and nutrient-focused dietary strategies.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- The journal paper was reviewed in full by the editorial team.
- Additional context and clarifications were added by staff to aid reader understanding.
About this metabolism and circadian rhythm research news
Author: Cassandra Falone
Source: Mass General Brigham
Contact: Cassandra Falone – Mass General Brigham
Image: Image credited to Neuroscience News
Original research: Open access. Paper: “Constant-routine protocol reveals an endogenous circadian rhythm in diet-induced thermogenesis with a peak in the biological morning” by Nina Vujović et al., published in Metabolism. DOI: 10.1016/j.metabol.2026.156655
Abstract
Constant-routine protocol reveals an endogenous circadian rhythm in diet-induced thermogenesis with a peak in the biological morning
Late meal timing has been linked to higher body mass, but the underlying physiology was unclear. Prior research suggested that the same meal generates a larger thermogenic response in the morning than in the evening, yet whether that difference results from behavior or from internal biological timing remained unresolved.
This randomized mechanistic study tested whether the endogenous circadian system modulates diet-induced thermogenesis independently of sleep/wake cycles, activity, posture, light exposure, and feeding patterns. Sixteen adults with overweight or obesity completed a 36-hour Constant Routine protocol featuring continuous wakefulness, dim light, semi-recumbent posture, a controlled environment, and identical meals every six hours.
Results showed a clear endogenous circadian rhythm in DIT, with a peak-to-trough amplitude equivalent to an approximately 44% difference (around 10 kcal per 4-hour interval) and timing consistent with a morning peak and an evening trough. After adjusting for circadian changes in fasting energy expenditure, the DIT rhythm remained significant, with somewhat reduced amplitude. Exploratory within-subject analyses indicated that this internal DIT rhythm was not altered by prior early versus late eating schedules. The findings suggest that a circadian peak in DIT during the biological morning may be one mechanism linking late meal timing to increased body mass.