Most of us have heard the advice not to eat right before bedtime, lest those late-night calories get stored as fat. But so far, this conventional wisdom has few long-term studies to back it up.
New research from the University of Pennsylvania suggests that cutting off food early may indeed be good practice.
Nine adults spent eight weeks eating a regular diet on an early schedule: three meals and two snacks between 8 a.m. and 7 p.m. The participants then took a two-week break, followed by eight weeks on a later eating schedule: the same amount of food, consumed from noon until 11 p.m.
While on the earlier schedule, the participants had lower levels of insulin and total cholesterol, said senior author Kelly Allison, director of the Center for Weight and Eating Disorders at Penn's Perelman School of Medicine.
On the early schedule, the participants also lost an average of 2.4 pounds during the eight-week period and had a lower "respiratory quotient" — an indicator that their bodies were burning more fat, Allison said. Their weights on the later eating schedule, on the other hand, stayed about the same.
The participants had an average body mass index of 22.4, well within normal range. (A woman whose height is 5-foot-6 and weighs 139 pounds would have a BMI of 22.4.) They were given amounts of food designed to maintain their body weights.
Unlike the changes in insulin and cholesterol, the changes in weight and fat-burning were not large enough to say for sure if they could have been due to chance. But the "effect size" — the amount of weight lost — was enough to suggest that eating earlier is not a bad idea, said the authors, who collaborated with Johns Hopkins University.
The preliminary results were presented in Boston this week at SLEEP 2017, a major academic conference on sleep research. Data from additional participants will be analyzed later.
It is not yet clear why the earlier schedule seemed to contribute to lower weight, the authors said. But it may in part be the common-sense explanation — that food consumed right before bed is not metabolized as readily because sleeping people are inactive, said lead author Namni Goel, a research associate professor at Penn.
She acknowledged that cutting off calories at 7 p.m. may be unrealistic for many.
"You have to live your life," Goel said. "But if you can do that 80 percent of the time, that seems to have benefits."
The participants wore wrist-mounted activity monitors to ensure that the altered eating schedules did not change their sleep patterns.
"We wanted them to keep their sleep constant to take that out of the equation," Allison said.
The authors plan future studies of people who are overweight or obese.
Stacey C. Cahn, a Rowan University psychologist who was not involved with the study, said that was a smart move. She also urged that future research include older people, as the participants in this study had an average age of 26.
"These are intriguing findings," Cahn said. "It would be important to know if these effects hold true for people who are older, people who are overweight, and people who have been overweight for a long time."
One reason that late-night calories may have more sticking power is the type of food eaten, said Cahn, who sees patients at Rowan's Wellness Center and also is a clinical associate professor.
When people are tired and their willpower is at a low ebb, they may grab carb-heavy pretzels and cookies rather than taking the time to whip up a "massaged kale salad," Cahn said.
"You're going to be more likely to reach for convenient foods that don't require a lot of preparation," she said.