The time you eat dinner in the evening significantly affects how many calories you burn during the day, your appetite and your adipose tissue — or adipose tissue — in your body, according to a study conducted by Harvard Medical School investigators at Brigham and Women’s Hospital.
The study, published in Cell Metabolism, found that late eating doubled the odds of being hungry, compared to early eating.
“Accumulating data suggest that eating earlier in the day is associated with lower body weight and improved weight loss success,” senior author Frank AJL Scheer, Ph.D., professor of medicine at Harvard Medical School and director of the Medical Chronobiology Program at Brigham and Women’s Hospital in Boston told Fox News Digital.
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Scheer, who is also a neuroscientist, said the study simultaneously looked at three mechanisms in the body that may explain weight gain associated with eating late.
The researchers said that previous studies suggest that eating late is associated with a higher risk of obesity and reduced success in losing weight – and the team wanted to understand why.
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“The three [mechanisms] was hunger regulation, how many calories we burn and changes in our adipose tissue,” Scheer said.
Sixteen participants in the study, he said, stayed in a laboratory to allow the investigators to control for other factors, such as how much and what the participants ate, their level of physical activity, their sleep, and the environmental temperature and light exposure — which might otherwise affect their measurements.
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“We found that late eating affected all three biological mechanisms, all in the direction that would promote weight gain,” says Scheer.
“Late eating increased hunger and appetite throughout the day (including related hormones), decreased the amount of calories burned during the day, and altered molecular pathways in adipose tissue that would promote fat growth.”
First author Nina Vujović, a researcher in the Medical Chronobiology Program, said in a Harvard University press release: “In this study, we asked, does the time we eat matter when everything else is held constant.”
The study’s 16 participants all had a body mass index considered in the overweight or obese range — and they followed specific laboratory protocols.
Each participant completed two different eating schedules: one where they followed a strict schedule for early meals – then another where they ate the same meals but four hours later in the day.
Two to three weeks before starting each of the laboratory target regimens, participants followed a fixed sleep-wake schedule; then, three days before entering the laboratory, participants followed strictly identical diets and meal schedules at home.
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“We found that eating four hours later makes a significant difference to our hunger levels, how we burn calories after we eat and how we store fat,” Vujović said in the press release.
The participants recorded their hunger and appetite levels and the researchers took blood samples throughout the day, checked the participants’ body temperature and measured their energy expenditure.
The researchers investigated how eating time affected how the body stores fat by taking biopsies of the participants’ adipose tissues during laboratory tests in both early and late eating protocols.
They compared the difference between the two eating routines.
Adipose tissue gene expression showed increased adipogenesis (fat storage) and decreased lipolysis (fat breakdown), which contributes to fat growth, according to the study.
The participants eating late also burned calories at a slower rate compared to the early eating schedule.
The investigators also said that eating late had a significant effect on the body’s hormones, leptin and ghrelin, which control appetite and a person’s desire to eat.
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They noted that leptin, which signals the body that you are full after a meal, decreased over a 24-hour period in the late eating schedule, compared to early eating.
“This study shows the effects of late versus early eating. Here, we isolated these effects by controlling for confounding variables such as caloric intake, physical activity, sleep and light exposure – but in reality, many of these factors can themselves be affected by meal timing,” Scheer said.
Dr. Reshmi Srinath, MD, director of the Mount Sinai Weight and Metabolism Management Program at Mount Sinai Health System in New York City, was not part of the study but commented on it to Fox News Digital.
“This is a small but very well-done study, supporting the need to avoid eating late at night given its impact on metabolism and hunger,” Srinath told Fox News Digital.
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“I usually advise patients to finish eating by 7.30-8pm and then leave the kitchen, so that they avoid excessive snacking and excessive caloric intake at night,” says Srinath, endocrinologist.
Laura Feldman, a registered dietitian nutritionist and assistant professor of nutrition at Long Island University in Brookville, New York, was not involved in the study but told Fox News Digital that the results may be difficult to replicate in everyday life.
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“The study was highly controlled,” she said. “Participants stayed in a laboratory environment for several days and all ate the same meals, participated in the same level of physical activity and had a fixed sleep schedule.”
“This is very different from the ‘real world’ scenarios that the average person” will encounter on a daily basis.
Most people, Feldman said, base their eating decisions on several factors beyond the timing of meals.
These factors include finances, work schedules, access to food, and stress and mental health.
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“It’s unclear whether these findings would still apply to some people, including night shift workers,” she told Fox News Digital.
The researchers acknowledged the challenge of real-world scenarios and feeding schedules.
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Scheer said in a press release, “In larger studies, where careful 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.”