People who eat a lot of fiber spend more time in deep sleep

Eating more fiber can help you sleep more deeply, while eating more fruits, vegetables, and nuts can help you fall asleep faster. That’s according to the most comprehensive look yet at how what we eat during the day affects how we sleep that night.

“Increasing fiber and plant varieties is already recommended for overall health, is low risk for most people, and may offer sleep benefits as an added benefit,” he says Hagai Rossman at the Weizmann Institute of Science in Israel.

Previous studies have linked eating high-fiber, plant-based foods to better sleep, but they mostly relied on people in surveys remembering their diet, sometimes weeks or months later. Furthermore, when sleep has been measured objectively, it has usually been with motion trackers, which cannot distinguish between its deeper and lighter phases, which is important for measuring sleep quality.

Now, Rossman and colleagues have obtained the clearest picture yet by analyzing sleep and eating data collected from more than 3,500 adults with an average age of 53. “Previous studies haven’t looked at as many dietary and sleep factors,” he says Marie-Pierre St-Onge at Columbia University in New York.

Over two consecutive days, each participant recorded what they ate in a mobile app, either during or shortly after consumption. At night, they wore a device approved by the US Food and Drug Administration to measure sleep. It consists of sensors on the chest, wrist and finger that monitor snoring, blood oxygen levels and heart and breathing rates.

The researchers used these measurements to estimate how long participants spent in different stages of sleep: light sleep (known as N1 and N2), deep, restorative sleep (N3), and rapid eye movement (REM) sleep, when dreams tend to be long and abstract.

Next, the researchers used a computational model to predict how 25 dietary factors affected sleep that night. They took into account factors that could have skewed the results, including age, gender, caffeine intake and – most importantly – data on diet and sleep from the previous day. “Controlling the previous day really allowed us to examine how what you eat during the day affects your next night’s sleep,” says Rossman.

The researchers found that participants who reported eating more fiber than the cohort average of 21 grams per day— equals approximately 2.5 cups of peas – tended to sleep better that night than people with below-average fiber intake. For example, the first group spent 3.4 percent more time in N3 and 2.3 percent less time in light sleep. “They’re moving toward restorative sleep, which is important for a healthier brain and body,” says St-Onge.

It’s not exactly clear why fiber has these effects, but studies suggest that gut microbes can ferment it into short-chain fatty acids like butyrate, which reduce inflammation and alter gut-to-brain signaling in a way that promotes deep sleep, Rossman says.

The researchers also found that those who had an above-average fiber intake had slightly lower heart rates during the night than those who consumed less. A low heart rate at night indicates that a person has entered a state of deep rest and recovery, which puts less strain on the heart. “Difference 1 beat per minute. [as observed between the high- and low-fibre groups] may not be so important overnight, but if the difference persists over a decade or a lifetime, it can make an important difference [for cardiovascular health]” says St-Onge.

Further analysis revealed that those who ate more than five types of plant foods per day also fell asleep slightly faster and had a lower heart rate during sleep than those who ate less. That could be because eating a wider mix of plants provides a variety of vitamins, minerals and other molecules, such as polyphenols, that help reduce inflammation and shift the nervous system into a rest-and-digest mode, Rossman says.

Future studies, ideally in sleep clinics that randomly assign people to eat different amounts of fiber and a wider or narrower range of plant foods, are needed to confirm the findings, St-Onge says.

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