The New York Times examines a growing body of research on the connections between food and sleep.
Much of what we know about sleep and diet comes from large epidemiological 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.
Some of these trials have also been funded by the food industry, which can bias results. One study funded by Zespri International, 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 funded by the cherry industry 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. Studies show that eating protein-rich foods such as milk and turkey on their own actually decreases the ability of tryptophan to cross the blood-brain barrier.