Late night couch snacking, movie popcorn on date night, all-nighters at the bar or in the library during finals week — there's food waiting to be eaten at all hours. Now researchers are finding when it’s eaten plays a key role in our lives. A San Diego State University team took a different approach to understanding weight gain and heart health by studying the when and not the what. Their findings, published in the journal Science, still reveal only a shadow of understanding a much larger and complicated link between sleep cycles and diet.

"So what's happening when people eat late? They're not changing their diet, just the time," the study’s coauthor Girish Melkani, a biologist at SDSU whose research focuses on cardiovascular physiology, said in a press release. "Time-restricted feeding would not require people to drastically change their lifestyles, just the times of day they eat. The take-home message then would be to cut down on the late-night snacks."

Any number of things could be going on inside a late-night snacker's body, but many of the cogs and wheels occur right inside the brain. Our internal clocks, which control sleep and wakefulness, can be traced down to a neurological level right inside our hypothalamus, a region in the brain where the optic nerve connects and communicates to the brain the level of light, or lack thereof, the eyes are exposed to throughout the day and night. Located directly above the optic nerve is the suprachiasmatic nucleus (SCN), which controls the body's internal clock, known as circadian rhythms. Once the SCN is stimulated by the light transmitted through the eye, the message travels along the optic nerve, ultimately regulating neural and hormonal activity based on our personal circadian rhythms.

For the study, researchers used fruit flies to mimic a human’s digestive and circadian rhythm by feeding them a standard diet of cornmeal, which they were allowed to eat whenever they wanted, including right before bed. Another group of flies were only allowed to eat within a 12-hour window, and after three weeks scientists saw a difference. The time restricted group slept better, didn’t gain as much weight, and had much healthier hearts than the free-range eaters. Each group followed the same diet, yet it was simply the timing that changed the outcome of their weight and heart health.

"In very early experiments, when we compared 5-week-old flies that were fed for either 24 hours or 12 hours, the hearts of the latter were in such good shape that we thought perhaps we had mistaken some young 3-week-old fruit flies for the older group," said the study’s lead author Shubhroz Gill, a postdoctoral researcher at SDSU. "We had to repeat the experiments several times to become convinced that this improvement was truly due to the time-restricted feeding."

Circadian rhythms are also known as the study of chronobiology. Each individual, regardless of age, has a specific chronotype, or internal timer, that is thought to be designed by our DNA and not by environmental factors. It is what is believed to determine whether a person is a morning person or a night owl. The neural and hormonal connection in the hypothalamus plays a key role in the intertwined relationship between sleep, food consumption, and the body’s natural clock. Meaning, it’s as much when you eat as it is what you eat. So consider cutting out late-night snacking and meals past 7 at night.

In addition to unraveling the increasingly distinct relationship between sleep deprivation and obesity, there is also evidence that the way the body digests nutrients, carbohydrates, and proteins is partially contingent on the time of day. For example, a growing body of research has shown a large breakfast can help the body prepare for the calorie-depleting activities during the day. Researchers are still unclear exactly what the optimal time to consume certain foods should be. It is also unclear if circadian rhythms, known as a biological pacemaker, have any effect on which foods are consumed at what time of day.

Source: Gill S, Melkani G, and Panda S. Time-restricted feeding attenuates age-related cardiac decline in Drosophila. Science. 2015.