Eating dinner at 5 p.m. may be healthier, study says

The early bird gets the worm.

A new study by Harvard Medical School researchers at Boston’s Brigham and Women’s Hospital suggests that eating earlier in the day might be better for us — and eating all meals within a 10-hour window could also be healthier.

The research, published in Cell Metabolism, found that the time of day we eat affects our hunger and appetite, energy levels and how the body stores fat.

“In this study, we asked, ‘Does the time that we eat matter when everything else is kept consistent?’” Nina Vujovic, a researcher in the hospital’s division of sleep and circadian disorders and author of the study, said.

Researchers asked 16 overweight participants to eat the exact same meals on two different schedules: one earlier in the day and the second about four hours later in the day. For example, one person might eat their meals at 9 a.m., 1 p.m. and 5 p.m. while someone in the latter group would eat at 1 p.m., 5 p.m. and 9 p.m.

The participants self-reported their hunger and appetite while researchers gathered blood samples, body temperature levels and energy expenditure. The investigators also took biopsies of adipose tissue to compare how the levels between the two eating patterns and gene expression patterns affected molecular pathways involved in adipogenesis — or how the body stores fat.

“We wanted to test the mechanisms that may explain why late eating increases obesity risk,” explained senior author Frank Scheer, a Harvard Medical School professor of medicine and director of the Medical Chronobiology Program in the Division of Sleep and Circadian Disorders at Brigham and Women’s. “Previous research by us and others had shown that late eating is associated with increased obesity risk, increased body fat and impaired weight loss success. We wanted to understand why.”

In the two to three weeks leading up to the study, participants had to maintain a strict sleeping and wake-up schedule, and in the last three days prior, they followed identical diets and meal schedules.

Results showed that late eating increased hunger, decreased energy expenditure, burned calories at a slower rate and altered the adipose tissue gene expression, which promotes fat growth, showing that all these changes combined may increase a risk in obesity. Eating later more than doubled the likelihood of increased hunger and generated lower levels of the hormone leptin, which is produced when we are full.

“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,” Vujovic said. 

Vujovic explained that these results were consistent with many other studies, but this one now shows how and why eating later might increase a risk in obesity. Researchers were able to detect changes in different control systems by using a random crossover study and with tightly controlled behavioral and environmental factors, including physical activity, posture, sleep and light exposure.

The researchers hope to eventually expand on the study to take into account other variables that might be present when not in a controlled setting.

“This study shows the impact of late versus early eating. Here, we isolated these effects by controlling for confounding variables like caloric intake, physical activity, sleep, and light exposure, but in real life, many of these factors may themselves be influenced by meal timing,” Scheer said. 

“In larger-scale studies, where tight 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.”

The study is good news for New Yorkers, who have started opting for a 5 p.m. dinner rather than a 8 p.m. meal.

According to the New York Times, New Yorkers are choosing to eat earlier in the day as a way to mark the end of their work day — since blurred lines between work and home life have become par for the course since the pandemic.

Margot Finn, a food studies lecturer at the University of Michigan, told the paper that 5 p.m. isn’t necessarily when people want to eat, but rather “when they want to be somewhere else.”