Eating late may trigger weight gain by increasing hunger and slowing metabolism, small study suggests

• Eating later in the day may influence weight gain by increasing hunger and slowing metabolism.
• A small new study found people were hungrier and burned fewer calories if they ate later in the day.

Late-night eating might contribute to weight gain by increasing hunger and decreasing the number calories you burn, new research suggests.

The habit may change levels of hunger hormones, metabolism, and fat storage, according to a study published October 4 in Cell Metabolism.

Researchers from Brigham and Women's Hospital, Harvard Medical School, and the University of Chicago looked at 16 adults with overweight or obesity as they followed two six-day meal plans — one with breakfast at 10 am, lunch at 2 pm, and dinner at 6 pm; and the other with each meal scheduled four hours later. The meals were otherwise identical.

The researchers wanted to test whether meal timing made a difference in appetite and metabolism if other factors like calories and ingredients were the same.

Participants were asked to rate how hungry they felt throughout the experiments, and researchers measured how many calories they were burning and how their hormone levels changed.

They found that participants were twice as likely to be hungry during the late-eating meal plan, and had lower levels of leptin, a hormone that signals fullness after eating, according to the data.

Late eaters also burned about 60 fewer calories each day, compared to when they ate earlier in the day.

Researchers also found that eating later in the day seemed to ramp up cellular processes for storing fat, and slow down processes associated with burning fat. The results suggest later eating may be linked to changes in the cells that promote an increase in fat tissue, although more research is needed to confirm it, the study authors wrote.

The findings could help explain why previous evidence has linked late-night eating to a higher risk of obesity, according to the researchers.

"In this study, we asked, 'Does the time that we eat matter when everything else is kept consistent?'" Nina Vujović, first author of the study and researcher at Brigham and Women's Hospital, said in a press release. "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."

However, the study was small, so the results need to be replicated with a larger group and broader population, including more women, since they made up fewer than half the participants in the most recent study. Researchers also noted that while they controlled for other lifestyle factors like total calorie intake, sleep times, exposure to light, and the amount of exercise participants got, many of these factors could make a difference in a real-world scenario.

For example, eating later at night could be related to how much sleep someone gets, and sleep deprivation has been shown to cause increases in hunger and calorie consumption. Some research has also also shown that late eating doesn't necessarily lead to weight gain.

For weight loss, the overall number of calories you eat still matters, so if that's your goal, focusing on eating fewer calories than you burn, regardless of meal timing.