Eat too much turkey and you’ll slip into a food coma. Snacking on cheese before bed will lead to nightmares. Drinking a glass of warm milk before bed will help you drift off into a peaceful sleep.
Everyone has heard these old superstitions about sleep and eating, but where’s the line between fact and fiction? What do we really know about eating and sleep, especially when it comes to eating a specific diet?
Both a lot and a little, it turns out. The intersection of specific diets and sleep has been an under-researched area of sleep science, but that’s starting to change. In recent years, more and more studies have begun to look at the impact of not just specific foods and nutrients on our sleep, but diet choices, as well. And while our diets can impact our sleep, our sleep can also affect our cravings and dietary habits, too.
How sleep impacts what we eat
As Dr. Marijane Hynes, a clinical professor of medicine at George Washington University in D.C. explains, it has been well documented in both individual studies and across literature reviews that insufficient sleep impacts our dietary choices. “People who sleep less than six hours [a night] tend to be more overweight,” Hynes says. “And it puts them at increased risk for heart diseases, diabetes, sleep apnea — a slew of diseases. You have to sleep to be healthy.”
The magic number? About seven and a half hours of sleep each night is the sweet spot. Sleeping less, especially six hours or less, leads to worse diets, and studies find a correlation of between getting too little sleep and consuming an extra 200 to 400 calories per day.
It’s not that people who are sleep deprived reach for more caffeine or sugary foods. In fact, some evidence suggests that not getting enough sleep decreases leptin, the hormone that tells you you’re full and triggers a disinterest in food. At the same time, a lack of sufficient sleep increases ghrelin, the hormone your stomach pumps out to tell your brain that it’s empty and it’s time to fill it up again.
“It’s a physiologic response,” Hynes explains. “Your hunger hormones get out of whack when you don’t get enough sleep.” She tends to see these impacts play out more with women, especially those with kids, who often choose to sacrifice sleep in order to have a little bit of “me time” at the end of the day. While Hynes says that she rarely sees patients who sleep too much, there have been studies that connect oversleeping with obesity, too. One 2008 study found that people who slept for nine or 10 hours a night were 21% more likely to become obese during a six-year period than people who slept seven or eight hours a night.
Insomnia, it turns out, seems to have a clearer relationship with diet. A 2016 literature review conducted in part by Dr. Marie Pierre St Onge, an associate professor of nutritional medicine at the Columbia University Medical Center, noted that research shows that individuals suffering from insomnia tend to have poor diets. “They can skip breakfast more frequently, they tend to have more sugar-sweetened beverages, and they [tend to] eat fewer vegetables and consume more sweet foods,” St-Onge says.
How what we eat impacts sleep
Just as our sleep impacts what we eat, our diets impact our sleep. But the relationships between diet and sleep are a bit more complex.
Susan Mitmesser, Ph.D., vice president of science and technology at Pharmavite, explains that food and sleep are just two legs of a three-legged stool that represents the core elements of human health. “I like to think of food (or diet) being one of the three pillars of good health. The other two include sleep and exercise. When you have one out of whack, the stool doesn’t stand quite as stably,” she says. “We shouldn’t think of these pillars of good health in complete isolation because they do impact each other.”
St Onge’s research supports Mitmesser’s stool analogy. Referencing a 2016 study, St Onge says, “We had participants in the lab. We gave them nine hours of sleep opportunity over four nights. And we gave them only the food they needed to maintain their body weight,” she says. The diet the researchers concocted was a more or less ideal, balanced diet — low in saturated fat and high in fiber — that few people adhere to outside of a laboratory setting.
After the first four nights, participants were allowed to select their own food intake. During it all, St Onge and company measured each participants’ sleep. “When we let them self-select their food intake, it took them longer to fall asleep, and they had less slow-wave sleep” — that is, non-REM or deep sleep, when the body repairs and recovers — “than when we gave them only the food they needed to maintain their weight.” Ultimately, they found that “participants who had more saturated fat, more simple sugars, and less fiber had less deep sleep, more arousal during their sleep, and more light stages of sleep.”
What does this all mean? That sleep and diet are deeply related to our health — especially, St Onge says, cardiovascular health. “Insufficient sleep is directly associated with increased cardiovascular risk. So, if you improve your diet to improve sleep, that could lead to improvement in cardiovascular health.”
Veganism, vegetarianism, the Mediterranean diet, and sleep
It’s clear that healthy eating can be a boon for sleep. But what kind of healthy eating? What about clean eating, vegan and vegetarian diets, and, in particular, the Mediterranean diet, which promotes lean protein, such as fish, as well as vegetables and nuts, seeds, and olive oil? These are popular dietary choices that can come with a number of health benefits (and some risks, too) — but how do they impact our sleep?
When it comes to red meat and processed meat intake, vegan and vegetarian diets and the Mediterranean diet can have some serious sleep benefits. Processed meats — anything smoked, barbecued, or cured — are high in saturated fat, which is known to cause inflammation. And when it comes to sleep, inflammation and catching Zzz’s don’t mix. Hynes notes that it’s likely the nitrates and other processing factors that make meats like bacon and sausage inflammatory. So, she wondered, might this inflammation have something to do with sleep apnea?
She answered that question with a 2018 study. While her endeavor lacked a control group, subsequent, larger studies have confirmed what she and her co-authors found: that processed meat is associated with sleep apnea. “It maybe is just high fat intake, but it’s really the processed meats, the large red meat intakes, that are associated with sleep apnea,” Hynes explains.
In the process, she and her co-authors came across a surprising finding that favors vegetarianism over veganism. “The people who came in with sleep apnea who had regular dairy consumption tended to have less severe sleep apnea,” Hynes notes. She went on to say that these patients still had sleep apnea, but it wasn’t as bad. “Milk from cows that’s nighttime milk, milk that’s gotten from cows at night when their melatonin is up, tends to help sleep. Malted milk helps people sleep,” she adds, noting that yogurt and kefir are promising, as well.
Eggs are another area where vegetarians or those following the Mediterranean diet can have an edge over vegans. “There are some micronutrients inversely associated with short sleep that are found in eggs, for example,” Mitmesser notes. This means that some of the nutrients in eggs can help with longer sleep.
But meat is a central pillar of diet in the United States. Americans eat more processed meat than they do fish, which can spell trouble on multiple levels. Not just because processed meat can get in the way of sleep, but also because fish is a primary focus of the Mediterranean diet, which studies find has sleep benefits.
Clean eating and sleep
When comparing a vegetarian, vegan, and clean-eating diet for their sleep benefits, so far it looks as if clean eating — eating foods that are as close to their natural state as possible — is likely the better way to go. A clean-eating diet that’s anchored in the Mediterranean diet (named for its general alignment with the diets of Italy, Greece, and other Mediterranean countries) might be particularly promising when focused on whole foods like vegetables, legumes, nuts, and seeds, supplemented with fish and whole grains. Along the Mediterranean, olive oil is the main source of added fat.
“We haven’t looked specifically at clean eating and those types of dietary strategies, but I would expect that those diets that are higher in fiber and lower in processed foods, solidum, and simple sugars will likely be associated with better sleep quality,” St Onge notes. “More fruits and vegetables and things like that would be considered to be associated with better sleep quality.”
Hynes says that the best way to go when it comes to diet and sleep is plants, plants, plants. “I just try to emphasize eating a lot of plants,” she says. “I think that we need to push for really healthy diets versus, you know, does it have to be vegetarian? Not necessarily. You can be healthy and not follow those diets.”
Both Hynes and Mitmesser advocate for flexitarian diets where you put an emphasis on fruits and vegetables while sprinkling in meat occasionally. “A variety of foods is really what we should aim for,” Mitmesser says. “I’m not here to judge or tell somebody that they need to eat a certain food group. What I am here to say is that if you are eliminating a food group, we know that there are these associations with things like short sleep. Therefore, you want to make sure that somehow, you get all the nutrients you need from the food group that you’re eliminating,” like calcium supplements for vegans.
Hynes agrees. “Eating mostly vegetables most of the time and then adding chicken or fish is probably, if you look at the whole thing from climate change to soil and everything else, the way to go.”