Few studies have thoroughly examined the simultaneous effects of late eating on the three main players in body weight regulation and thus obesity risk: regulation of calorie intake, the number of calories you burn, and molecular changes in fat tissue. Popular healthy diet mantras discourage midnight snacking, but few studies have investigated the effects of late eating on all three players simultaneously. Researchers from 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 metabolism, hunger, and biochemical pathways in adipose tissue. Cell Metabolism has reported its findings.

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"We wanted to test the mechanisms that may explain why late eating increases obesity risk," according to senior author and director of Brigham's Division of Sleep and Circadian Disorders Frank A. J. L. Scheer, Ph.D., medical chronobiology program. "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?'” noted the study's first author Nina Vujovic, PhD, a researcher in the Brigham's Division of Sleep and Circadian Disorders' Medical Chronobiology Program. "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."

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16 patients with a body mass index (BMI) in the overweight or obese range were the subject of a study by Vujovic, Scheer, and their colleagues. Each participant did two lab protocols: one with an exact early meal schedule and the other with the same meals timed exactly four hours later in the day. Participants kept set sleep and wake times in the final two to three weeks before beginning each in-lab regimen, and in the final three days before entering the lab, they closely adhered to similar meals and meal times at home. Participants frequently kept track of their hunger and appetite in the lab, gave us numerous times during the day tiny blood samples, and had our researchers assess their body temperature and energy expenditure.

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

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To make their findings more applicable to a larger population, Scheer's team plans to increase the proportion of female participants in subsequent trials. Although there were only five female participants in this study cohort, the study was designed to control for the menstrual phase, which reduced confounding but made it more challenging to get women to participate. In the future, Scheer and Vujovic want to learn more about how the link between mealtime and nighttime affects energy balance.