Obesity afflicts approximately 42
percent of the U.S. adult population and contributes to the onset of chronic
diseases, including diabetes, cancer, and other conditions. While popular
healthy diet mantras advise against midnight snacking, few studies have
comprehensively investigated 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. A new study by investigators from Brigham and Women’s Hospital, a founding member of the Mass General Brigham healthcare system, found that when
we eat significantly impacts our energy expenditure, appetite, and molecular
pathways in adipose tissue. Their results are published in 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, PhD, 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 Vujovic, PhD, 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.”
Vujovic, Scheer and
their team studied 16 patients with a body mass index (BMI) in the overweight
or obese range. Each participant completed two laboratory protocols: one with a
strictly scheduled early meal schedule, and the other with the exact same
meals, each scheduled about four hours later in the day. In the last two to
three weeks before starting each of the in-laboratory protocols, participants maintained
fixed sleep and wake schedules, and in the final three days before entering the
laboratory, they strictly followed identical diets and meal schedules at home.
In the lab, participants regularly documented their hunger and appetite,
provided frequent small blood samples throughout the day, and had their body
temperature and energy expenditure measured. 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.
Vujovic 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 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 menstrual phase,
reducing confounding but making recruiting women more difficult. Going forward,
Scheer and Vujovic 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."
Source: https://www.brighamandwomens.org/about-bwh/newsroom/press-releases-detail?id=4268
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