Eating Late Changes Your Fat Tissue and Decreases Calories Burned

New research provides experimental evidence that late eating reduces energy expenditure, increases hunger, and changes fat tissue, all of which may raise the risk of obesity.

About 42% of adults in the United States are obese, which increases the risk of developing chronic diseases including diabetes, cancer, and other conditions. While popular healthy diet mantras warn against midnight snacking, few studies have thoroughly studied the combined impacts of late dining on the three key factors in body weight regulation and therefore obesity risk: calorie intake regulation, calorie burn, and molecular changes in fat tissue.

Researchers at Brigham and Women’s Hospital, a founding institution of the Mass General Brigham healthcare system, discovered in a recent study that the timing of meals has a big impact on our energy expenditure, appetite, and molecular pathways in adipose tissue. Their findings were recently published in the journal Cell Metabolism. 

“We wanted to test the mechanisms that may explain why late eating increases obesity risk,” explained senior author Frank A. J. L. Scheer, Ph.D., Director of the Medical Chronobiology Program in the Brigham’s Division of Sleep and Circadian Disorders. “Previous research by us and others had shown that late eating is associated with increased obesity risk, increased body fat, and impaired weight loss success. We wanted to understand why.”

“In this study, we asked, ‘Does the time that we eat matter when everything else is kept consistent?’” said first author Nina Vujović, Ph.D., a researcher in the Medical Chronobiology Program in the Brigham’s Division of Sleep and Circadian Disorders. “And we found that eating four hours later makes a significant difference for our hunger levels, the way we burn calories after we eat, and the way we store fat.”

A total of 16 individuals with a body mass index (BMI) in the overweight or obese range were examined by Vujovi, Scheer, and their colleagues. Every participant completed two lab protocols: one with a rigidly planned early meal schedule and the other with the exact same meals, each set for around four hours later in the day.

Participants maintained set sleep and waking times for the last two to three weeks before beginning each of the in-laboratory protocols, and they closely followed similar diets and meal schedules at home for the last three days before entering the laboratory. In the lab, participants underwent regular body temperature and energy expenditure monitoring, frequent small blood sample collection throughout the day, and regularly recorded their hunger and appetite.

To measure how eating time affected molecular pathways involved in adipogenesis, or how the body stores fat, investigators collected biopsies of adipose tissue from a subset of participants during laboratory testing in both the early and late eating protocols, to enable comparison of gene expression patterns/levels between these two eating conditions.

Results revealed that eating later had profound effects on hunger and appetite-regulating hormones leptin and ghrelin, which influence our drive to eat. Specifically, levels of the hormone leptin, which signals satiety, were decreased across the 24 hours in the late eating condition compared to the early eating conditions. When participants ate later, they also burned calories at a slower rate and exhibited adipose tissue gene expression towards increased adipogenesis and decreased lipolysis, which promote fat growth. Notably, these findings convey converging physiological and molecular mechanisms underlying the correlation between late eating and increased obesity risk.

Vujović explains that these findings are not only consistent with a large body of research suggesting that eating later may increase one’s likelihood of developing obesity, but they shed new light on how this might occur. By using a randomized crossover study, and tightly controlling for behavioral and environmental factors such as physical activity, posture, sleep, and light exposure, investigators were able to detect changes in the different control systems involved in energy balance, a marker of how our bodies use the food we consume.

In future studies, Scheer’s team aims to recruit more women to increase the generalizability of their findings to a broader population. While this study cohort included only five female participants, the study was set up to control for the menstrual phase, reducing confounding but making recruiting women more difficult. Going forward, Scheer and Vujović are also interested in better understanding the effects of the relationship between meal time and bedtime on energy balance.

“This study shows the impact of late versus early eating. Here, we isolated these effects by controlling for confounding variables like caloric intake, physical activity, sleep, and light exposure, but in real life, many of these factors may themselves be influenced by meal timing,” said Scheer. “In larger scale studies, where tight control of all these factors is not feasible, we must at least consider how other behavioral and environmental variables alter these biological pathways underlying obesity risk. ”

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