Why Eating Late At Night Can Be Bad For Your Weight


There is some disagreement regarding the precise time you should stop eating for the day. When someone stops, eating is influenced by various factors, including appetite, habits, culture, work schedules, individual preferences, and social contexts. Everyone has an opinion about when to stop eating, but it needs to be clarified whether these opinions are supported by scientific evidence.

Due to the belief that eating past bedtime results in weight gain, many people are curious about when to stop eating at night. It is a well-known fact that consuming more than your body requires results in weight gain. As a result, you risk gaining weight if you frequently eat after midnight in addition to your usual meals. This popular wisdom is also supported by some studies that link eating later in the day with a higher risk of obesity and slower weight reduction following weight loss surgery.

However, according to researchers from Brigham and Women’s Hospital who published the findings of a brand-new randomized, controlled, crossover study in the journal Cell Metabolism, little research has been done on how the timing of eating affects physiological mechanisms. They, therefore, sought to examine the mechanisms that would explain why eating later raises the chance of becoming obese and made some intriguing findings, which we will summarize in this article.

Answering Why Late-Night Eating Increases Risk of Obesity

Sixteen participants in the study had a body mass index (BMI) that fell within the overweight or obese category. Their average age was 37, and their age ranged from 25 to 59. 11 men and 5 women took part. The study reports that one Hispanic, three Asian, and five Black subjects participated.

Participants have to be in good health to be chosen for the study. They also mentioned consistently eating breakfast and engaging in consistent amounts of physical activity.

In the previous twelve months, none had performed shift work. Except for birth control and one person who used hypertension medicine throughout, none of the individuals used caffeine, alcohol, nicotine, or any other substance for the two weeks before each testing session.

No perimenopausal women participated in this trial. To avoid hormone spikes around ovulation, pre-menopausal women were scheduled to participate at specified points in their menstrual cycles.

Participants underwent two 9-day laboratory stays at the Brigham and Women’s Hospital Center for Clinical Investigation. The interval between each laboratory visit was 3 to 12 weeks.

Additionally, participants got ready for the study by going to bed and waking up on the same schedule for two to three weeks before they arrived at the lab for the initial stay. Wearing wrist actigraphy enabled researchers to keep track of how long individuals spent in bed during a predetermined, fixed 8-hour period.

In addition, participants kept sleep diaries and left time-stamped voicemails before bed and after waking up.

The participants were also told to adhere to identical diets and meal regimens for three days before arriving at the lab.

Temperature and light levels were closely regulated in the facility. Participants were prohibited from having visitors and were not permitted to use phones, radios, or the internet. They didn’t work out. Each room had a video camera to monitor compliance.

Participants followed set diets of predetermined nutrients during each stint at the lab. The early meal participants ate their first meal one hour after waking up and then every 250 minutes after that.

Every meal was planned for a 4-hour later time slot under the late meal schedule. Participants were timed as they ate, and no meal exceeded 30 minutes.

The Findings of The Study

The findings showed that eating later significantly impacted the hunger and appetite-controlling chemicals leptin and ghrelin, which has implications for our desire to eat. Leptin levels, which indicate fullness, were lower over 24 hours in the late meal condition than in the early feeding condition.

Participants who ate later burnt calories more slowly and showed altered gene expression in their fatty tissue, encouraging greater adipogenesis and decreased lipolysis. These results reveal convergent physiological and molecular mechanisms that underlie the association between eating later in the day and a higher risk of obesity.

On the late-eating schedule, the subset of subjects who consented to a biopsy showed altered adipose tissue gene expression toward enhanced adipogenesis and decreased lipolysis, which promotes fat growth.

The results demonstrate that eating after a certain time regularly changed the biochemical and physiological systems involved in controlling energy intake, expenditure, and storage—each of these three in a manner that promotes weight gain.

The study’s authors also noted that this is the first to show how late eating affects adipose tissue. Therefore, future research will be required to determine how various signals are combined at the adipose tissue level to produce the observed alterations in gene expression.

Journal Reference

Vujović, N., Piron, M. J., Qian, J., Chellappa, S. L., Nedeltcheva, A., Barr, D., Heng, S. W., Kerlin, K., Srivastav, S., Wang, W., Shoji, B., Garaulet, M., Brady, M. J., & Scheer, F. A. J. L. (2022). Late isocaloric eating increases hunger, decreases energy expenditure, and modifies metabolic pathways in adults with overweight and obesity. Cell Metabolism, 34(10). https://doi.org/10.1016/j.cmet.2022.09.007 

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