Hunger increases and fat burning slows down if you eat later in the day, according to research


We all know that eating later in the day is not good for our waistline, but why? A new study measured that question by comparing people who ate the same foods, but at different times of the day.

“Does the time we eat matter when everything else is held 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 doubles your chances of feeling more hungry, according to research published Tuesday in the journal Cell Metabolism.

“Eating four hours later makes a significant difference in our hunger levels, the way we burn calories after eating, and the way we store fat,” said Vujović. “Together, these changes explain why late eating is associated with the increased risk of obesity reported in other studies, and may provide new biological insight into the underlying mechanisms.”

The study supports that circadian rhythms, which affect key physiological functions such as body temperature and heart rate, affect the way our bodies absorb fuel, the researchers said.

The study shows that eating later “increases appetite, affects hormones and also changes gene expression, especially in fat metabolism, with a tendency toward less fat breakdown and more fat deposition,” said Dr. Bhanu Prakash Kolla, professor. is a consultant in psychiatry and psychology at the Mayo Clinic College of Medicine and Mayo’s Center for Sleep Medicine and Division of Addiction Medicine.

While previous studies have linked later eating to weight gain, this study did not measure weight loss and cannot show a causal link, said Kolla, who was not involved in the study. In addition, studies have shown that skipping breakfast is linked to obesity, he said.

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

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

“Although there have been other studies investigating why eating late is associated with an increased risk of obesity, this may be the most well-controlled, including careful monitoring of meal size, composition and timing, physical activity, sleep, room temperature and light exposure,” he said. said lead author Frank Scheer, director of the Medical Chronobiology Program at Brigham’s Division of Sleep and Circadian Disorders.

All participants were in good health, without diabetes or a history of shift work, which may affect circadian rhythms, and were regularly physically active. Each person in the study maintained a strict sleep/wake schedule for about three weeks and prepared meals at fixed times for three days before the start of the laboratory experiment.

The participants were then randomly divided into two groups. One group ate calorie-controlled meals at 8:00 a.m., 12:00 p.m., and 4:00 p.m., while the other ate four hours later, at noon, 4:00 p.m., and 8:00 p.m., on the six days outlined in the study. Measures of appetite and hunger were collected 18 times each, and tests of body fat, temperature, and energy expenditure were collected on three days.

After a few weeks of rest, the same participants reversed the procedure: the early eaters were transferred to the late eater group and vice versa, thus using each person as their own control.

The results showed that hunger pangs doubled for those on the night eating regimen. Those who ate later in the day also reported craving starchy and salty foods, meat and, to a lesser extent, dairy and vegetables.

Looking at the blood test results, the researchers were able to see why: levels of leptin, a hormone that tells us when we feel full, were lower in late eaters than in late eaters. In comparison, levels of the hormone ghrelin, which stimulates our appetite, increased.

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

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

Participants who ate later in the day also burned calories at a slower rate than when they ate earlier. Their body fat tests found gene changes that would affect how fat is burned or stored, the study found.

“These changes in gene expression would support fat tissue growth by forming more fat cells, as well as fat storage,” Scheer said.

It is not known whether these effects will continue over time, or in people currently taking medications for chronic disease, who were excluded from this study. More research is needed, the authors said.