Circadian fasting. Circadian rhythm eating. Early bird dinners. Eating with your body clock. In recent months, these terms have made the rounds on social media, with creators claiming that timing your meals with your circadian rhythm—or internal clock—can have positive effects on everything from sleep to metabolic health to weight management.

Specifically, many seem to advocate eating your first meal in the morning, shortly after waking, and your last meal several hours before sleep.

At a time when people are increasingly optimizing all facets of health, it’s not surprising that something as simple as shifting meal times has generated excitement. But does eating in sync with your circadian rhythm actually do anything for your health?

The strategy is based on the idea that eating in alignment with your internal clock helps synchronize your body, leading to benefits.

Your internal clock refers to the roughly 24-hour rhythm that regulates many processes in the body. It’s controlled by a central clock in the brain, which is synchronized by environmental clues, like morning sunlight. It’s this clock that prepares your body to function during the day and recover at night.

When you shift mealtimes earlier, the cycle for organs involved in digestion, such as the liver and intestines, may become more aligned with the brain’s central clock, indicating a healthy circadian system, explained Andrew W. McHill, PhD, an associate professor and director of the Sleep, Chronobiology, and Health Laboratory at the Oregon Health and Science University School of Nursing.

However, eating at times that conflict with the central clock—most notably late at night, when the body is preparing for sleep and recovery—can create inconsistency.

In recent years, a growing body of research has explored whether that misalignment might lead to health problems, leading some people to focus more on when they eat—not just what they eat.

What Happens When You Don’t Eat With Your Circadian Rhythm?

“We do know that what we call circadian misalignment is associated with the development of disease,” said Mireille Serlie, MD, PhD, a professor of internal medicine (endocrinology) at the Yale School of Medicine.

Studies in rodents have found that eating out of sync with normal circadian rhythms can have a range of detrimental health effects.12

“In animal literature, when mice are eating at the wrong time, they gain more weight, even when they’re eating the same amount of calories. And they have all sorts of other issues,” McHill said. “They can get higher rates of cancer, infertility—you name it, it basically gets bad.”

Humans aren’t mice, of course. But Serlie said that research has also shown that shift workers—who frequently experience circadian misalignment, including eating during the biological night, when the brain would expect rest—have a higher risk of obesity, insulin resistance, type 2 diabetes, and cardiovascular disease.

Periods without food are necessary for transitioning our bodies into maintenance processes such as autophagy, in which damaged or unnecessary cellular components are broken down and recycled, Serlie explained.

“If the central clock thinks, okay, it’s time to go to sleep or to rest, and then your liver all of a sudden has to deal with a McDonald’s meal, that’s not good,” she said.

So, Does That Mean Circadian Eating Offers Benefits?

Even so, it’s not yet fully understood whether the reverse of circadian misalignment—eating in sync with the body’s central clock—translates to clear health benefits.

Some of the research is promising. Studies have suggested that earlier eating schedules may improve in metabolic measures such as insulin sensitivity, body fat percentage, blood pressure, and blood sugar control.3456

However, most studies on circadian eating have been small and short-term, said Amy Shah, MD, a double-board-certified medical doctor and nutritionist.

It’s also hard to know how different groups, such as men and women, respond to circadian eating, and whether any possible benefits stem from the eating pattern itself or from the fact that limiting the eating window can lead people to consume fewer calories, she said.

“We think it’s a circadian mechanism. Others think it could be a reduced eating duration mechanism,” McHill said. “It might be some combination of both.”