Eating all your meals within a six-hour window sounds like some sort of fad diet (and a recipe for midnight fridge raids). But a small new study suggests that having your dinner before 2 p.m.(!)—or skipping it entirely—actually reduces hunger cravings and boosts fat burn. Before you sign on for the super early–bird special, however, here’s what you should know.
The study's preliminary results (not yet published in an academic journal) were presented this week at the Obesity Society’s annual meeting. It’s the first human trial of “early time-restricted feeding,” a strategy in which people eat their last meal of the day by mid-afternoon and don’t eat again until breakfast.
This type of eating plan has shown promise in animal studies; mice who are fed time-restricted diets tend to lose more body fat and have lower risk of chronic diseases than those whose meals are more spaced out. Some researchers believe that similar schedules could be beneficial for people as well, since human metabolism follows an internal clock and many aspects of it function best in the morning.
To test this strategy, researchers at Louisiana State University's Pennington Biomedical Research Center followed 11 overweight men and women, ages 20 to 45, over two four-day periods. During one period, they ate all of their meals between 8 a.m. and 2 p.m.; during the other, they followed an average American eating schedule with meals between 8 a.m. to 8 p.m. Both diets included the same daily calorie amounts and were similar except for timing. On the last day of each diet, the researchers performed 24 hours of metabolic testing on the participants, and asked about their hunger levels.
The time-restricted diet did not affect how many calories the participants burned. But it did reduce their daily hunger swings, and increased the amount of fat they burned during several hours at night. It also improved metabolic flexibility, the body’s ability to switch between burning carbohydrates and fat.
So could restricting meals to a smaller time window help with weight loss, or improve other aspects of health? The researchers don’t know, but they say it’s a possibility.
“We found that eating between 8 a.m. and 2 p.m. followed by an 18-hour daily fast kept appetite levels more even throughout the day, in comparison to eating between 8 a.m. and 8 p.m.,” said lead author Courtney Peterson, PhD, assistant professor of nutrition sciences at the University of Alabama Birmingham, in a press release. "It may therefore positively impact body composition both by increasing fat oxidation and by reducing energy intake," the study concludes.
Dale Schoeller, PhD, professor emeritus in the University of Wisconsin’s Department of Nutritional Sciences, says the findings do suggest—for the first time in people—that meal timing does have an impact on metabolism.
“With additional research on early-time restricted feeding on humans, we can create a more complete picture of whether this innovative method can best help prevent and treat obesity,” said Schoeller, who is a spokesperson for the Obesity Society and was not involved in the study.
But there are also reasons to take these findings with a grain of salt, says Christine Gerbstadt, MD, RD, author of Doctor’s Detox Diet.
The metabolic effects of meal timing is an “interesting question,” says Dr. Gerbstadt, but she points out that the study’s test group was very small and only included young and (besides being overweight) healthy adults.
“It is unlikely that these results can be generalized to all Americans,” she told Health after reviewing the study’s abstract—especially those who are older, who have health conditions such as diabetes, high blood pressure, or high cholesterol, and those with poor exercise habits.
Potential risks for these and other groups—like how medications might be affected by such a schedule change—have not been studied, she says.
“The control of hunger has financial and health benefits, but I question the safety of daily fasting in all American populations,” she says, referring to the long gap between dinner and breakfast. “Certainly children and adults over 50 should be warned not to try this.”
Plus, deciding to eat such an early dinner every day—or no dinner at all—would require a major change for most people, behaviorally and socially. (Doing it just once in a while wouldn’t likely be recommended, as irregular meal schedules have been tied to higher levels of obesity and health complications.)
“This eating pattern does not suit the lifestyles of most,” Dr. Gerbstadt says, “and may or may not be of any benefit.”