Summary: A new controlled study provides a clear mechanistic link between late-night eating and weight gain. Researchers show that the body’s internal 24-hour clock independently controls diet-induced thermogenesis (DIT) — the extra energy burned to digest, absorb, transport, and store nutrients — producing a strong daily rhythm in how many calories are burned after a meal.
While prior research has observed slower metabolism later in the day, it was unclear whether that change was driven by behavior (sleep, activity, light exposure) or by an intrinsic biological clock. Using a rigorous laboratory protocol that removes behavioral and environmental influences, the investigators isolated the endogenous circadian effect and found a pronounced metabolic peak in the biological morning (around 7:00 AM) and a clear trough in the biological evening (around 7:00 PM), independent of when participants actually woke or moved.
Key Facts
- The Circadian Peak: Diet-induced thermogenesis (DIT) naturally reaches its highest level in the biological morning, approximately 7:00 AM, increasing the calories burned to process food early in the day.
- The Evening Trough: The internal clock lowers DIT to its minimum in the biological evening, around 7:00 PM, so an identical meal consumed at night is processed with less caloric cost.
- Gold-standard Protocol: Researchers used the Constant Routine protocol to hold posture, lighting, temperature, wakefulness, and nutritional delivery constant, isolating internal circadian effects from external influences.
- Independent of Behavior: The daily variation in post-meal calorie burn is driven by the endogenous circadian system, not by sleep/wake cycles, physical activity, or light exposure.
- Implications for Weight Management: This internal rhythm helps explain why delayed meal timing can reduce total calories burned during waking hours and make weight loss more difficult.
- Clinical Timing Guidance: The results support chronobiology-based recommendations to concentrate larger meals earlier in the day to align eating with peak metabolic capacity.
Source: Mass General Brigham
Study overview
Researchers in the Sleep and Circadian Disorders group at Mass General Brigham examined whether the human circadian system independently controls diet-induced thermogenesis. Han-Chow Koh, PhD, and Frank A.J.L. Scheer, PhD, co-led the study, which was published in 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 study matters
Epidemiological and experimental evidence have linked late eating to higher body weight. Earlier work by this team showed that delaying mealtimes by several hours reduces calories burned across waking hours. However, it remained unclear whether that effect was produced by behavioral factors or by a true internal clock. This study addresses that gap by testing whether DIT follows an endogenous circadian rhythm.
Methods
The investigators used the Constant Routine (CR) protocol, a gold-standard method in circadian biology that removes changing environmental and behavioral influences. Participants remained awake for 36 hours in a semi-recumbent posture under continuous dim light and stable room temperature, receiving identical meals every six hours. This design reveals rhythms driven by internal biology rather than by sleep, activity, or light.
Results
Sixteen adults with overweight or obesity completed the protocol. The data showed a robust endogenous circadian rhythm in DIT: a peak in the biological morning and a trough in the evening. The peak-to-trough amplitude was approximately 44% (about 10 kcal per 4-hour window), centered near ∼8:00 AM and ∼8:00 PM. After adjusting for circadian variation in fasting energy expenditure, the DIT rhythm remained significant with similar timing but a somewhat reduced amplitude (peak ∼7:00 AM, trough ∼7:00 PM; about 29%, roughly 7 kcal per 4-hour window).
Exploratory within-subject analyses suggested that this endogenous DIT rhythm was not altered by prior early versus late eating schedules. These findings identify an internal metabolic mechanism that likely contributes to the association between late mealtimes and increased body mass.
Key Questions Answered:
A: Diet-induced thermogenesis is the temporary increase in metabolic rate after eating, reflecting the energy required to digest, absorb, transport, and store nutrients. It is a meaningful component of total daily energy expenditure. Because the internal clock maximizes DIT in the morning (around 7:00 AM) and reduces it by the evening (around 7:00 PM), the same meal can require substantially more energy to process in the morning than at night, which affects how many calories are available for storage.
A: In normal life, behavior and environment change together with the circadian cycle, making it hard to separate their effects. The Constant Routine protocol removes these changes by keeping participants awake, in a stable posture, under dim light and constant temperature while providing identical snacks on a fixed schedule. Any remaining rhythmic changes in DIT under these conditions can be attributed to the endogenous circadian system.
A: Timing of food intake matters. Aligning the largest meals with the biological morning, when DIT is highest, can increase daily energy expenditure from digestion. Conversely, consuming large meals late in the evening occurs when DIT is at its lowest, reducing calorie burn from digestion and potentially promoting calorie storage.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- The underlying journal paper was reviewed in full by editorial staff.
- Additional context was added by the editorial team to clarify clinical and behavioral implications.
About this metabolism and circadian rhythm research news
Author: Cassandra Falone
Source: Mass General Brigham
Contact: Cassandra Falone – Mass General Brigham
Image: The image is credited to Neuroscience News
Original Research: Open access. “Constant-routine protocol reveals an endogenous circadian rhythm in diet-induced thermogenesis with a peak in the biological morning” by Nina Vujović, Han-Chow E. Koh, Su Wei Heng, Priyanka Panjwani, Charlotte Van Zee, Wei Wang, Jingyi Qian, Marta Garaulet, Frank A.J.L. Scheer. 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 associated with higher body mass, but the physiological mechanisms have been unclear. Prior studies found that identical meals generate a larger thermogenic response when eaten in the morning than in the evening, yet it was uncertain whether this difference reflected behavior and environment or a true circadian effect.
To test whether the endogenous circadian system modulates diet-induced thermogenesis independently of sleep/wake, activity, posture, light exposure, and fasting/eating cycles, 16 adults with overweight or obesity (12 males; mean age 36 ± 11 years; BMI 28.8 ± 2.4 kg·m−2; HbA1c 5.4 ± 0.3%) completed a 36-hour Constant Routine protocol. Participants remained continuously awake in a semi-recumbent posture under dim light and received identical test meals every six hours.
The results demonstrated a significant endogenous circadian rhythm in DIT, with a peak-to-trough amplitude of ~44% (≈10 kcal per 4 hours), peaking in the biological morning and reaching a trough in the biological evening (statistical significance p = 0.005; approximate timing ∼8 AM and ∼8 PM). After adjusting for circadian changes in fasting energy expenditure, the DIT rhythm remained significant with similar timing but reduced amplitude (peak ∼7 AM, trough ∼7 PM; ~29%, ≈7 kcal per 4 hours; p = 0.026).
Exploratory analyses indicated that prior early versus late eating schedules did not modify this endogenous DIT rhythm. The documented circadian peak in morning DIT may be one mechanism linking late meal timing to greater body mass.
Funding: This study was supported by the National Institutes of Health (NIH) (R01DK099512).
Disclosures: Dr. Scheer reports consulting or advisory relationships 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 with Novartis Institutes for BioMedical Research Inc., and an employment and equity relationship with Novartis Pharmaceuticals Corporation.