When it comes to healthful eating, what you eat is important. But when you eat also might matter, too.
For decades, researchers have observed some associations between meal timing and health consequences. In particular, habitually later meals seem to be problematic. People who eat meals late at night — for example, within two hours of going to bed — might be more prone to become overweight, and night-shift workers are at a higher risk of developing type 2 diabetes.
Why late meals have such effects still eludes researchers. And though there’s interest in targeted nutritional science, which would tell people exactly when to sit down to dinner to get the perfect metabolic response, “we’re still a bit out of reach of that goal. What and when you eat are both issues,” says Jonathan Jun, a pulmonary disease physician at Johns Hopkins University.
For now, many researchers are still focused on understanding some of the broader public health concerns — such as obesity, heart disease, and diabetes — that might be related to eating late at night. And there’s a lot left to learn.
So far, the research suggests that our bodies prefer to process nutrients during the day. Our circadian rhythms, the internal cycles that help regulate when we sleep and when we are awake, influence a host of biological systems. Genes producing proteins needed for, say, muscle firing might be more or less active depending on the time of day, Jun says. Likewise, there might be a similar relationship between food consumption and when the body is the most efficient at breaking it down.
Researchers aren’t totally sure why some bodily activities function best during the day or night, but research in rodents suggests that the “sleep” portion of circadian cycles allows cells to repair themselves. “Cells use that time to clean house, so to speak,” says Adrian Vella, an endocrinologist at the Mayo Clinic. It might be that eating too close to this rest and relaxation period forces cells to delay self-repair in favor of digestive processes — a delay that, if it happens too often, might start to cause harm.
Blood-sugar regulation is another example that might illustrate this theory. Studies have found that eating dinner late at night — or even eating on a flipped schedule, as a night shift worker would — tends to elevate blood-sugar levels more than standard mealtimes do. It’s a pattern that’s based on mealtime and is independent of the type of food consumed.
Some researchers speculate that melatonin — the sleep hormone that peaks at night — might repair the machinery that helps sugar enter our cells. It might be that if people eat close to bedtime, the body is both entering its repair-mode and inefficiently processing an influx of sugars at the same time. In other words, it’s a bit like trying to assemble a car while building the factory. How much influence melatonin has over this single metabolic process is just a theory for now, but…