When we eat can determine how hungry we'll be afterward, study finds

Eating late is associated with an increased risk of obesity 0:48

(CNN) -- 

We all know that eating late in the day is not good for our waistlines, but why?

A new study looked at this question by comparing people who ate the same foods, but at different times of the day.

The question driving the study was "does it matter what time we eat if everything else is held constant?" explained lead study author Nina Vujović, a researcher in the Division of Circadian and Sleep Disorders at Brigham Hospital. and Women's of Boston.

The answer was yes: eating later in the day will double the chances of being hungrier, according to the study published Tuesday in the academic journal Cell Metabolism.

"We found that eating four hours later makes a significant difference to our hunger levels, the way we burn calories after eating, and the way we store fat," Vujović said.

"Taken together, these changes may explain why eating late is associated with an increased risk of obesity, according to other studies, and provide new biological insight into the underlying mechanisms."

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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.

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The study shows that eating later causes "an increase in hunger, affects hormones and also changes the expression of genes, especially with regard to fat metabolism, with a tendency towards less breakdown of fats and a buildup," says Bhanu Prakash Kolla, MD, professor of psychiatry and psychology at Mayo Clinic School of Medicine and consultant to the Center for Sleep Medicine and the Division of Addiction Medicine.

While previous studies have linked eating later to weight gain, this study didn't measure weight loss and can't show a cause-and-effect relationship, said Kolla, who wasn't involved in the study.

Also, research has shown that skipping breakfast is linked to obesity, she said.

"So could these results be the result of skipping breakfast instead of eating late? That's an effect to watch out for in this study," Kolla said.

strict control

The study was small -- just 16 overweight or obese people -- but 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 controlled, as it includes strict control of the quantity, composition and timing of meals, physical activity , sleep, room temperature and light exposure," said lead author Frank Scheer, director of the Medical Chronobiology Program in the Division of Sleep and Circadian Disorders at Brigham.

All participants were in good health, had no history of diabetes or night shift work, which can affect circadian rhythm, and engaged in regular physical activity.

All study participants followed a strict sleep-wake schedule for about three weeks and received prepared meals at set times for three days before starting the lab experiment.

The participants were then randomly distributed into two groups.

One group ate calorie-controlled meals at 8 a.m., noon and 4 p.m., while the other group ate the same meals four hours later at noon, 4 p.m. and 8 p.m. the night during the six days that the study lasted.

Hunger and appetite measures 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 moved to the group of those who ate later and vice versa, thus using each person as their own control.

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More hunger, less fat burned

The results showed that the desire to eat doubled for those who followed a night-time eating regimen.

People who ate later in the day also reported a greater desire for salty, starchy foods and meat and, to a lesser extent, a craving for dairy and vegetables.

By looking at the results of the blood tests, the researchers were able to see why: Levels of leptin, a hormone that tells us when we feel full, decreased in people who ate later, compared to those who ate earlier.

Along the same lines, levels of the hormone ghrelin, which triggers our appetite, increased.

"What's new is that our results show that eating late leads to an increased ratio of ghrelin to leptin over the entire 24-hour sleep-wake cycle," says Scheer.

In fact, the study found that the ratio of ghrelin to leptin increased by 34% when eaten later.

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"These changes in hormones that regulate appetite dovetail well with increased hunger and appetite with late meals," Scheer said.

When the participants ate later they also burned calories at a slower rate than when they ate earlier.

According to the study, analyzes of their body fat detected changes in genes that influence how fat is burned or stored.

"These changes in gene expression would favor the growth of adipose tissue by forming more fat cells, as well as increasing fat storage," said Scheer.

It is not known whether these effects would be sustained over time, or in people currently taking medications for chronic conditions, who were excluded from this study.

The authors note that more studies are needed.

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