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Does What You Eat Affect How You Sleep?

What we're learning about the link between carbs, protein, and better sleep.

Source: Lolostock/Shutterstock

Do you frequently struggle to get enough sleep? If so, you’re in good company: More than a third of adults in the United States regularly log less than the seven to eight hours of sleep that most people need in order to feel rested, function well, and protect their health. More than a 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 solutions—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 its study has been overlooked, especially in comparison to many other forms of sleep treatment.

50 Years of Research on Diet and Sleep

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 on how nutrition and modifications to diet might affect and improve sleep. These studies were conducted over a 50-year period, from 1965 to 2015. Most took place under laboratory conditions, but a smaller number were conducted under real-life conditions.

Their findings don’t provide a clear answer to the question of the potential role of diet in improving sleep. Perhaps the clearest takeaway from the analysis is this: Given the scope of sleep problems we face, there is a need for more research on the impact of nutrition.

Although they are mixed, the results of the researchers’ analysis are still worth a review. The team looked at 21 studies conducted over the 50-year period. Of these, 17 were laboratory investigations, and the remaining four took place in 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, eight returned results showing improvements to sleep as a result of dietary intervention. But none of the four non-laboratory studies demonstrated an effect of nutrients on sleep. The 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 is that the effects of nutrition on sleep are relatively small.

What Diet May Do to Sleep

Among the studies that showed effects, there are indications that nutrition and diet may impact sleep in different ways.

Carbohydrate intake. Studies show that carbohydrate levels in one's diet are associated with changes to sleep behavior and sleep architecture, including time spent in slow-wave sleep and REM sleep. Several studies in the review link 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 are also 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.

Other research associated consumption of a high-carbohydrate meal four hours before bedtime with reduced sleep latency onset (the time it takes to fall asleep after going to bed).

Protein intake. 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 carbohydrates increases the efficacy of tryptophan in the brain. One study shows that tryptophan in combination with carbohydrates significantly reduces the amount of time participants are 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: Eating solid meals reduced sleep latency onset, as compared to liquid meals. And mixed-composition meals—meals that include a combination of carbohydrates, protein, and fat—may decrease time in slow-wave sleep during the initial sleep cycle of the night. According to one study, mixed-composition meals, when eaten at midday, may increase the duration of sleep for several hours after eating.

Limits to What We Know

This is a small group of studies, and it’s not possible to draw hard conclusions from such limited research. Most of the studies examined the acute effects of nutrition over sleep, which might transpire over a very short-term observation period. There’s little (if any) research that tracks the longer-term impact of dietary interventions on sleep.

What’s more, nearly all of the studies looked at the impact of nutritional intervention on healthy sleepers. People with sleep troubles might show greater benefit from diet modifications than people who already sleep well.

Society has a sleep problem that isn’t getting any better, despite our significant reliance on prescription and over-the-counter sleep medications. It’s time to pay more attention to the possible role that nutrition might play in improving our sleep.

Sweet dreams,

Michael J. Breus, PhD
The Sleep Doctor™

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