Adults who ate more fiber on a given day spent more of that night in deep sleep and REM sleep, with a slower heart rate. That is the finding of a new preprint from researchers at the Weizmann Institute of Science.
The wearable-based analysis tracked 4,793 nights of sleep across 3,598 adults. Diet was captured in real time through a mobile food log, and sleep was scored by an overnight sensor that also read breathing and heart rate.
On days with higher fiber density, participants spent 0.59 percentage points more of the night in deep sleep and 0.76 percentage points more in REM sleep. Light sleep dropped by 1.35 percentage points.
Average nighttime heart rate fell by 1.14 beats per minute. The differences are modest but consistent across a large sample.
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The paper is a preprint that has not yet been peer-reviewed. The design was observational, and the authors flag that residual confounding cannot be fully ruled out, so eating more fiber has not been proven to cause deeper sleep.
Which foods drove the signal
Two other patterns pointed the same way. Greater plant-food diversity was tied to falling asleep about 0.68 minutes faster, plus a lower overnight heart rate. A higher share of whole-plant foods in the day's eating showed a similar heart-rate drop.
In practice, that points to the fiber staples authorities already flag as underused, such as beans, lentils, oats, whole-wheat bread and a broad mix of vegetables and fruit.
Cleveland Clinic notes that women aged 19 to 30 need about 28 grams of fiber a day and men in that age group about 34 grams. Only about 5% of American adults hit those numbers, with most averaging around 16 grams.
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How fiber may reach the brain
The likely link runs through the gut. Fiber that reaches the colon is fermented by resident bacteria into short-chain fatty acids such as butyrate, acetate and propionate.
A review in the journal Nutrients notes that these acids have been detected in human cerebrospinal fluid, and that they can influence the production of serotonin and GABA, the brain's main inhibitory neurotransmitter and one closely tied to sleep.
Human evidence is still thin. In animal work cited by that review, giving mice a source of butyric acid raised non-REM sleep by nearly 50%, but the effect has not been mapped as cleanly in people.
For readers who feel routinely tired, the practical takeaway is modest. Small day-to-day shifts toward more plants and more fiber may show up that same night in the way the body sleeps, adding another layer to a growing pile of research linking specific everyday foods to sleep quality.
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This article is made and published by Jesper Bengtson, who may have used AI in the preparation.