The researchers discovered that eating more saturated fat and less fiber from foods like vegetables, fruits and whole grains led to reductions in slow-wave sleep, which is the deep, restorative kind. In general, clinical trials have also found that carbohydrates have a significant impact on sleep: People tend to fall asleep much faster at night when they consume a high-carbohydrate diet compared to when they consume a high-fat or high-protein diet. That may have something to do with carbs helping tryptophan cross into the brain more easily.
But the quality of carbs matters. In fact, they can be a double-edged sword when it comes to slumber. Dr. St-Onge has found in her research that when people eat more sugar and simple carbs — such as white bread, bagels, pastries and pasta — they wake up more frequently throughout the night. In other words, eating carbs may help you fall asleep faster, but it is best to consume “complex” carbs that contain fiber, which may help you obtain more deep, restorative sleep.
“Complex carbohydrates provide a more stable blood sugar level,” said Dr. St-Onge. “So if blood sugar levels are more stable at night, that could be the reason complex carbohydrates are associated with better sleep.”
One example of a dietary pattern that may be optimal for better sleep is the Mediterranean diet, which emphasizes such foods as vegetables, fruits, nuts, seeds, legumes, whole grains, seafood, poultry, yogurt, herbs and spices and olive oil. Large observational studies have found that people who follow this type of dietary pattern are less likely to suffer from insomnia and short sleep, though more research is needed to confirm the correlation.
But the relationship between poor diet and bad sleep is a two-way street: Scientists have found that as people lose sleep, they experience physiological changes that can nudge them to seek out junk food. In clinical trials, healthy adults who are allowed to sleep only four or five hours a night end up consuming more calories and snacking more frequently throughout the day. They experience significantly more hunger and their preference for sweet foods increases.
In men, sleep deprivation stimulates increased levels of ghrelin, the so-called hunger hormone, while in women, restricting sleep leads to lower levels of GLP-1, a hormone that signals satiety,
“So in men, short sleep promotes greater appetite and desire to eat, and in women there is less of a signal that makes you stop eating,” said Dr. St-Onge.