The science on diet and sleep
Do you struggle to get enough sleep on a regular basis? If so, you’re in plentiful company. More than a third of adults in the U.S. are regularly logging less than the 7-8 hours of sleep that most people need in order to feel rested, function well, and protect their health. More than one quarter of U.S. adults say they frequently contend with insufficient sleep.
This all-too-common state of sleep deprivation sends millions of people in search of aids to better rest—often, through prescription and over-the-counter sleep aids, but also through other sleep therapies, including cognitive-behavioral sleep treatments, exercise, mindfulness, meditation and stress-reduction techniques, and herbal supplements.
But what about diet? Can dietary modifications play a role in improving sleep? The impact of nutrition as a therapeutic tool for helping sleep is not yet well understood. There is research that suggests dietary adjustments may indeed improve sleep. But the study of nutrition as means by which to improve sleep has been overlooked, compared to many other forms of sleep treatment.
50 years of diet-sleep research
A group of scientists from several U.S. universities teamed up to take a closer look at what’s known about the effectiveness of nutrition as a therapeutic tool for sleep. They conducted a comprehensive review of studies that looked at how elements of nutrition and modifications to diet might affect and improve sleep. The studies they examined were conducted over a 50-year period, from 1965 to 2015. Most of the studies took place under laboratory conditions, but a smaller number of the studies were conducted under natural, real-life conditions.
Their findings don’t provide a clear-cut answer to the question of diet and nutrition’s possible role in improving sleep. Perhaps the clearest takeaway from the analysis is this: given the scope of sleep problems we face, there is s real need for more scientific attention to the subject of nutrition’s potential impact on sleep behavior.
However mixed, the results of researchers’ analysis are interesting, and worth looking at in some detail. Scientists looked at a total of 21 studies conducted over the 50-year period. Of these 21 studies, 17 were laboratory investigations, and the remaining four studies took place in participants’ real-life settings.
Diet and sleep—in the lab and in life
The difference between laboratory and non-laboratory studies proved significant. Among the 17 laboratory trials, slightly less than half—eight studies—returned results showing improvements to sleep as a result of dietary intervention. Among the four in natura studies, none demonstrated an effect from nutrients on sleep.
Why might these out-of-laboratory nutrition studies have failed to show an effect over sleep? Researchers point to possible explanations, including the challenge of managing diet manipulations under real-life conditions, and the use of healthy sleepers as subjects, as opposed to people with sleep problems. Another possible explanation? The effects of nutrition to improve sleep are relatively small.
What diet may do to sleep
Among the studies that did show effects, there are indications that nutrition and diet may impact sleep in several different ways.
Carbohydrate intake and sleep. Studies showed carbohydrate levels in the diet were associated with changes to sleep behavior and sleep architecture, including time spent in slow-wave sleep and in REM sleep. Several of the studies included in the review linked low-carbohydrate diets to increased time spent in slow-wave sleep—a deep and physically restorative sleep stage—and high-carbohydrate diets to less time in this deep-sleep stage.
Levels of carbohydrate intake also were linked to changes in the duration of REM sleep: one study linked low-carbohydrate diet to less time in REM sleep, while another study linked both low-carbohydrate and high-carbohydrate diets to more time in REM sleep.
Research associated consumption of a high-carbohydrate meal 4 hours before bedtime with reduced sleep latency onset—that’s the time it takes to initially fall asleep after going to bed.
Protein intake and sleep. Research found that increasing levels of tryptophan from dietary protein sources improved symptoms of insomnia. Tryptophan is an amino acid that boosts sleepiness. Dietary sources of tryptophan include many protein-rich foods, such as eggs, poultry, dairy, nuts, seeds, and soybean. The presence of carbohydrate increases the efficacy of tryptophan in the brain. One study showed that tryptophan in combination with carbohydrate significantly reduced the amount of time participants spent awake at night.
Research also found that evening-timed increases to dietary tryptophan reduced next-day sleepiness and increased next-day attention levels, probably as a result of improving sleep.
Several studies compared the composition of meals—high-carbohydrate versus high-fat, as well as solid-nutrient meals versus liquid nutrients—and revealed some interesting details about the diet-sleep connection. These studies found that eating solid meals reduced sleep latency onset (that’s the time it takes to first fall asleep), as compared to liquid meals. They found that mixed-composition meals—meals that include a combination of carbohydrate, protein, and fat—may decrease time in slow-wave sleep during the initial sleep cycle of the night. When eaten at midday, mixed-composition meals may increase the duration of sleep for several hours after eating, according to one of the studies reviewed.
Limits to what we know of diet and sleep
There are a few things to keep in mind when looking at these results. First, this is a small group of studies, and it’s not possible to draw hard conclusions from such limited research. Most the studies examined the acute effects of nutrition over sleep, effects that might transpire over a very short-term observation period. There’s little if any research that exists that tracks the longer-term impact of dietary interventions for sleep.
What’s more, among the 21 studies examined in this review, nearly all of them looked at the impact of nutritional intervention on healthy sleepers. People with sleep troubles might show greater benefit from diet modifications than people who are already sleeping well.
We have a society-wide sleep problem that isn’t getting any better, despite significant reliance on prescription and over-the-counter sleep medications. It’s time to pay more sustained attention to the possible role that nutrition may plan in helping to improve sleep.
Michael J. Breus, PhD
The Sleep Doctor™