When you eat can dictate how hungry you are, study finds

A new study comparing people who ate the same foods, but at different times of the day. (Superstar, Shutterstock)

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ATLANTA – We all know that eating later in the day isn’t good for our waistline, but why? A new study weighed in on this question by comparing people who ate the same foods, but at different times of the day.

“Does it matter what time we eat when everything else is consistent?” said first author Nina Vujović, a researcher in the division of sleep and circadian disorders at Brigham and Women’s Hospital in Boston.

The answer was yes. Eating later in the day will double your chances of feeling hungrier, study finds published Tuesday in the journal Cell Metabolism.

“We found that eating four hours later made a significant difference to our hunger levels, how we burn calories after eating, and how we store fat,” Vujović said. “Together, these changes may explain why eating late is associated with an increased risk of obesity reported by other studies and provide new biological insights into the underlying mechanisms.”

The study supports the concept that the circadian rhythm, which influences key physiological functions such as body temperature and heart rate, affects how our bodies absorb fuel, the researchers said.

The study shows that eating later leads to “increased hunger, impacts hormones and also alters gene expression, particularly in terms of fat metabolism with a trend towards less fat breakdown and more fat deposits,” said Professor Dr. Bhanu Prakash Kolla. in Psychiatry and Psychology at Mayo Clinic College of Medicine and Consultant at Mayo’s Center for Sleep Medicine and Division of Addiction Medicine.

While previous studies have linked eating later with weight gain, this study did not measure weight loss and cannot show causation, said Kolla, who does not did not participate in the study. Additionally, research has shown that skipping breakfast is linked to obesity, he said.

“So could these results be the result of skipping breakfast rather than eating late? That’s an effect to consider for this study,” Kolla said.

Tightly controlled

The study was small — just 16 overweight or obese people — but carefully planned to rule out other potential causes of weight gain, the authors said.

“Although there have been other studies examining why eating late is associated with an increased risk of obesity, this can best be controlled, including strict control of quantity, composition and mealtimes, physical activity, sleep, ambient temperature and light exposure,” said lead author Frank Scheer, director of the medical chronobiology program in Brigham’s division of sleep and circadian disorders.

All participants were in good health, with no history of diabetes or shift work, which can affect circadian rhythm, and had regular physical activity. Each person in the study followed a strict schedule of healthy wakefulness and sleep for about three weeks and received prepared meals at set times for three days before the start of the lab experiment.

The participants were then randomized into two groups. One group ate calorie-controlled meals at 8 a.m., noon, and 4 p.m., while the other ate the same meals four hours later at noon, 4 p.m., and 8 p.m. for the six days reported in the study. . Hunger and appetite measurements were collected 18 times each while body fat, temperature and energy expenditure tests were collected on three separate days.

After a break of a few weeks, the same participants reversed the procedure – those who had eaten earlier switched to the late meal group and vice versa, thus using each person as their own control.

More hunger, less fat burned

The results showed that feelings of hunger doubled for those who ate at night. People who ate later in the day also reported cravings for starchy and savory foods, meats, and to a lesser extent dairy and vegetable cravings.

By examining blood test results, researchers were able to figure out why: Levels of leptin, a hormone that tells us when we’re feeling full, decreased in late eaters compared to early eaters. In comparison, levels of the hormone ghrelin, which stimulates our appetite, have increased.

“What’s new is that our results show that eating late causes an increase in the average ratio of ghrelin to leptin across the entire 24-hour sleep/wake cycle,” Scheer said. In fact, the study found that the ratio of ghrelin to leptin increased by 34% when meals were eaten later in the day.

“These changes in appetite-regulating hormones correlate well with increased hunger and appetite with a late meal,” Scheer said.

When participants ate later in the day, they also burned calories at a slower rate than when they ate earlier. Their body fat tests revealed changes in genes that would impact how fat is burned or stored, according to the study.

“These changes in gene expression would promote fat tissue growth through the formation of more fat cells, as well as increased fat storage,” Scheer said.

It’s unclear whether these effects would continue over time, or on people currently taking medication for chronic conditions, who were excluded from this study. Further study is needed, the authors said.

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