Summary: A breakthrough study from researchers provides a definitive mechanistical link between late-night eating and weight gain. The research demonstrates that the body’s internal 24-hour clock independently controls diet-induced thermogenesis (DIT), the energy expended and calories burned to process, digest, and store nutrients after a meal.
While scientists have long observed that human metabolism slows down later in the day, it remained an open question whether this fluctuation was merely a byproduct of behavioral cycles (such as sleep, physical activity, and light exposure) or driven by a true biological clock.
Utilizing the specialized “Constant Routine” laboratory protocol to strip away all environmental and behavioral confounders, the team isolated the endogenous circadian rhythm. Their findings revealed that our internal clock causes a robust metabolic peak in the biological morning (around 7:00 AM), while hitting its absolute lowest point in the biological evening (around 7:00 PM), independent of when a person actually wakes up or moves.
Key Facts
- The Circadian Peak: Diet-induced thermogenesis ($DIT$) naturally peaks in the biological morning at approximately 7:00 AM, maximizing the thermal and caloric cost of digesting food early in the day.
- The Evening Trough: The body’s internal clock independently drops $DIT$ to its lowest baseline values in the biological evening at approximately 7:00 PM, meaning fewer calories are burned processing identical meals at night.
- The Gold-Standard Protocol: The study used a highly controlled “Constant Routine” laboratory environment, keeping posture, dim lighting, temperature, wakefulness, and nutritional delivery constant to isolate pure internal rhythms.
- Independent of Behavior: The dynamic shift in calorie-burning efficiency is driven completely by the endogenous circadian system, entirely independent of sleep/wake cycles, physical activity, or light changes.
- Weight Management Mechanics: This independent rhythm provides a biological framework explaining why delayed mealtimes cause individuals to burn fewer total waking calories and struggle more with weight loss.
- Clinical Timing Implications: These findings validate evidence-based chronobiology recommendations, supporting shifting major caloric intake toward the morning hours to optimize metabolic health.
Source: Mass General
Sleep and circadian disorders researchers at Mass General Brigham published results from a recent study showing that the bodyโs internal clock independently influences diet-induced thermogenesis (DIT), or the extra calories burned after eating.
Han-Chow Koh, PhD, and Frank A.J.L. Scheer, PhD, of theย Medical Chronobiology Programย 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 inย Metabolism, โConstant-routine protocol reveals an endogenous circadian rhythm in diet-induced thermogenesis with a peak in the biological morning.โ
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)โhow much energy the body spends processing and storing nutrients after eatingโvaries at different times of the day, with higher levels in the morning versus the evening. However, itโs 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 โbody clockโ).
Q: What central question(s) were you investigating?
Essentially, we wanted to find out whether thereโs a rhythm in energy expenditure after eating thatโs 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 systemโs 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.
Authorship: In addition to Koh and Scheer, Mass General Brigham authors include Nina Vujoviฤ, Su Wei Heng, Priyanka Panjwani, Charlotte Van Zee, Wei Wang and Jingyi Qian. Additional authors include Marta Garaulet.
Paper cited: Vujoviฤ N., et al. โConstant-routine protocol reveals an endogenous circadian rhythm in diet-induced thermogenesis with a peak in the biological morning.โ Metabolism. DOI: 10.1016/j.metabol.2026.156655
Funding: This study was supported by the National Institutes of Health (NIH) (R01DK099512).
Disclosures: Scheer reports a consulting or advisory relationship with The University of Alabama at Birmingham, Morehouse School of Medicine and Salk Institute for Biological Studies. Vujoviฤ reports a consulting or advisory relationship with Novartis Institutes for BioMedical Research Inc. Vujoviฤ also reports a relationship with Novartis Pharmaceuticals Corporation that includes employment and equity or stocks.
Key Questions Answered:
A: Diet-induced thermogenesis is the temporary boost in metabolic rate that happens after eating as your body expends energy to break down, absorb, transport, and store nutrients. It represents a significant portion of your total daily energy expenditure. Knowing that our internal biological clock naturally maximizes this processing engine at 7:00 AM and suppresses it by 7:00 PM means that the exact same sandwich eaten at dinner requires less physical energy to process than if eaten at breakfast, leaving more residual calories to potentially be stored as fat.
A: In normal daily life, it is impossible to separate your clock from your behaviors, you eat because you are awake, and your metabolism shifts because you are moving around in the light. The Constant Routine protocol solves this by placing human subjects in an unvarying laboratory environment for an extended period. Participants remain awake in a semi-recumbent posture, under continuous dim lighting, in a temperature-controlled room, while receiving identical nutritional snacks evenly spaced out across the hours. By removing changes in sleep, light, and movement, any remaining metabolic waves can be attributed solely to the body’s internal master clock.
A: The core takeaway is that when you eat can be just as biologically relevant as what you eat. Shifting your heaviest meals earlier into the morning hours works in tandem with your natural evolutionary biochemistry, maximizing the amount of heat and energy your body expends during digestion. Conversely, eating large meals late in the evening forces your digestive system to process nutrients at a time when your internal master clock has dialed your thermogenic engine down to its lowest baseline, decreasing your overall daily calorie burn.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this metabolism and circadian rhythm research news
Author:ย Cassandra Falone
Source:ย Mass General Brigham
Contact:ย Cassandra Falone โ Mass General Brigham
Image:ย The image is credited to Neuroscience News
Original Research:ย Open access.
โConstant-routine protocol reveals an endogenous circadian rhythm in diet-induced thermogenesis with a peak in the biological morningโ by Nina Vujoviฤ, Han-Chow E. Koh, Su Wei Heng, Priyanka Panjwani, Charlotte Van Zee, Wei Wang, Jingyi Qian, Marta Garaulet, Frank A.J.L. Scheer.ย 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 increased body mass, although the physiological mechanisms are unknown. While previous research has suggested that identical meals consumed in the morning produce greater thermogenic responses than evening meals, it is unclear whether this is due to endogenous circadian control or due to behavioral and environmental factors.
Therefore, this mechanistic randomized trial tested whether the endogenous circadian system, thus independently of sleep/wake, rest/activity, body posture, dark/light, and fasting/eating cycles, modulates diet-induced thermogenesis (DIT).
To unmask endogenous circadian effects from environmental and behavioral confounds, 16 healthy adults with overweight or obesity (12 males; meanย ยฑย SD age, 36ย ยฑย 11ย years; BMI, 28.8ย ยฑย 2.4ย kgยทmโ2; HbA1c, 5.4ย ยฑย 0.3%) completed a gold-standard Constant Routine (CR) protocol, consisting of 36ย h of continuous wakefulness, rest, semi-recumbent posture, dim light, and identical test meals every 6ย h.
The data demonstrated a significant endogenous circadian rhythm in DIT, with a peak-to-trough amplitude of 44% (โผ10ย kcal/4ย h), a peak during the biological morning and a trough in the evening (pย =ย 0.005; equivalent to โผ8ย am/โผ8ย pm, respectively). After adjusting for the circadian rhythm in fasting energy expenditure, the circadian rhythm in DIT remained significant with similar circadian timing, although with slightly reduced amplitude (โผ7ย am/โผ7ย pm; โผ29%; โผ7ย kcal/4ย h;ย pย =ย 0.026).
In exploratory analyses using an experimental within-subject design, data revealed that this endogenous circadian rhythm in DIT was not affected by prior early versus late eating schedules. The endogenous circadian rhythm in DIT, with a peak in the biological morning, may be one of the mechanisms contributing to the reported link between late meal timing and increased body mass.
