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Eating late increases hunger and changes fat tissues

Obesity affects over 42 percent of Americans and contributes to the onset of a variety of chronic diseases, including diabetes and cancer. While midnight snacking is considered by many to have a negative impact on health, few studies have comprehensively investigated the effects of late eating on the three main factors contributing to body weight regulation and thus obesity risk: the regulation of calorie intake, the number of burned calories, and molecular changes in fat tissue. Now, a research team from Brigham and Women’s Hospital has found that when we eat significantly impacts our energy expenditure, appetite, and molecular pathways in adipose tissue.

“In this study, we asked, ‘Does the time that we eat matter when everything else is kept consistent?’” said study lead author Nina Vujović, an expert in Medical Chronobiology at Bingham. “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.”

The scientists studied 16 participants with a body mass index (BMI) in the overweight or obese range. Each of them had to complete two laboratory protocols – one with an early meal schedule, and the other with the exact same meals, each scheduled approximately four hours later in the day. For two or three weeks before starting the experiment, participants had to maintain a fixed sleeping schedule, and in the final three days before entering the laboratory, they followed identical diets and meal schedules.

In the lab, participants had to document their hunger and appetite levels, provide frequent blood samples throughout each day, and have their body temperature and energy expenditure measured. To assess how eating schedules affected the molecular pathways involved in adipogenesis – the way in which the body stores fat – the experimenters collected biopsies from a subset of the participants in both the early and late eating protocols.

The analyses revealed that eating later had a profound effect on the hunger- and appetite-regulating hormones leptin and ghrelin. For instance, the levels of leptin, which signals satiety, were decreased in the late eating condition. Moreover, late eaters burned calories at a slower rate and exhibited adipose tissue gene expression towards increased adipogenesis and decreased lipolysis, which promotes fat growth.

Since this study only involved five female participants, the researchers aim to recruit more women in future studies to increase the generalizability of the results. 

“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 senior author Frank Scheer, the director of the Medical Chronobiology Program at Bingham. “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.” 

The study is published in the journal Cell Metabolism.

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By Andrei Ionescu, Staff Writer

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