This has not been a very good year for sleep.
With the coronavirus pandemic, school and work disruptions and a contentious election season contributing to countless sleepless nights, sleep experts have encouraged people to adopt a variety of measures to overcome their stress-related insomnia. Among their recommendations: engage in regular exercise, establish a nightly bedtime routine and cut back on screen time and social media.
But many people may be overlooking another important factor in poor sleep: diet. A growing body of research suggests that the foods you eat can affect how well you sleep, and your sleep patterns can affect your dietary choices.
Researchers have found that eating a diet that is high in sugar, saturated fat and processed carbohydrates can disrupt your sleep, while eating more plants, fiber and foods rich in unsaturated fat — such as nuts, olive oil, fish and avocados — seems to have the opposite effect, helping to promote sound sleep.
Much of what we know about sleep and diet comes from studies that, over the years, have found that people who suffer from consistently bad sleep tend to have poorer quality diets, with less protein, fewer fruits and vegetables, and a higher intake of added sugar from foods like sugary beverages, desserts and ultra-processed foods. But by their nature, epidemiological studies can show only correlations, not cause and effect. They cannot explain, for example, whether poor diet precedes and leads to poor sleep, or the reverse.
To get a better understanding of the relationship between diet and sleep, some researchers have turned to randomized controlled trials in which they tell participants what to eat and then look for changes in their sleep. A number of studies have looked at the impact of a diverse array of individual foods, from warm milk to fruit juice. But those studies often have been small and not very rigorous.
Some of these trials have also been funded by the food industry, which can bias results. One study the world’s largest marketer of kiwi fruit, for example, found that people assigned to eat two kiwis an hour before their bedtime every night for four weeks had improvements in their sleep onset, duration and efficiency. The authors of the study attributed their findings in part to an “abundance” of antioxidants in kiwis. But importantly, the study lacked a control group, so it is possible that any benefits could have resulted from the placebo effect
Other studies have found that drinking tart cherry juice can modestly improve sleep in people with insomnia, supposedly by promoting tryptophan, one of the building blocks of the sleep-regulating hormone melatonin. Tryptophan is an amino acid found in many foods, including dairy and turkey, which is one of the reasons commonly given for why so many of us feel so sleepy after our Thanksgiving feasts. But tryptophan has to cross the blood-brain barrier to have any soporific effects, and in the presence of other amino acids found in food it ends up competing, largely unsuccessfully, for absorption.Eating protein-rich foods such as milk and turkey on their own actually decreases the ability of tryptophan to cross the blood-brain barrier.
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One way to enhance tryptophan’s uptake is to pair foods that contain it with carbohydrates. That combination stimulates the release of insulin, which causes competing amino acids to be absorbed by muscles, in turn making it easier for tryptophan to cross into the brain, said Marie-Pierre St-Onge, an associate professor of nutritional medicine at Columbia University Irving Medical Center and the director of the Sleep Center of Excellence at Columbia.
Dr. Gong has studied the relationship between diet and sleep. Her work suggests that rather than emphasizing one or two specific foods with supposedly sleep-inducing properties, it is better to focus on the overall quality of your diet. She and her colleagues recruited 26 healthy adults and controlled what they ate for four days, providing them regular meals prepared by nutritionists while also monitoring how they slept at night. On the fifth day, the subjects were allowed to eat whatever they wanted.