There’s an obvious connection between what we eat and how we sleep (take down a bowl of five-alarm chili a few hours before bedtime and you’ll most likely spend the night cursing all chipotles that ever were or ever will be). But there’s more of a relationship between sleep and metabolic function than a gnarly bout of heartburn: the two acts are knotted together and too much or not enough of one greatly affects the other.
Like sleep and body weight. There’s a sold body of evidence linking sleep deprivation with a higher BMI, likely because we crave fatty foods when we’re exhausted. Studies suggest, too, that what we eat and when can determine how quickly we fall asleep. It’s a complex, interconnected world.
It’s also one that’s constantly being explored. Here’s what we know right now about the association already. Keep it in mind next time you chow down. And lay off the midnight chili.
1. We Crave Carb-heavy, Fatty Foods when We’re Tired.
In a recently published paper, researchers from the University of Chicago that a lack of sleep appears to affect the natural endocannabinoid system in our brains thought to be affected when we ingest marijuana; in other words? Going without sleep triggers provides the same uncontrollable case of the munchies as smoking pot.
Another a small study of 11 men and women published in the Journal of Clinical Nutrition in 2009 concluded that participants in a group restricted to five-and-a-half hours of sleep per night tended to eat more of their calories in the form of snack foods, and carb-heavy snacks in particular. The group able to sleep for eight-and-a-half hours were better able to stick to normal, healthier meals.
Researchers noted a similar tendency toward high-carb and fatty foods in sleep-deprived people in a study of 225 adults published in SLEEP in 2013. The rest-restricted group ate more calories during the day and at night, but showed a greater intake of mostly carb-heavy and high-fat foods.
Tired subjects in a 2013 study appeared to move more to keep themselves awake during the day but ended up overcompensating in the food department, eating way more than necessary to fuel the extra energy expenditure, concluded researchers at the University of Colorado Sleep and Chronobiology Laboratory. But this paper noted a positive flipside: When people got adequate amounts of sleep, however, they ate less carbohydrates and fat and were able to lose weight.
Why does all of this happen? Lack of sleep seems to raise certain hunger-controlling hormones, which causes us to lose our inhibition (and hip-check people to get some pomme frites)
2. The Bacteria in Our Gut Affects Our Sleep and Wake Cycle. And Vice Versa.
Or so it seems. Scientists are just beginning to grasp how gut microbes affect our circadian rhythms, an area that might play a role in regulating when we eat as well as when we sleep and wake. Since gut microbes appear to affect levels of cortisol, a stress hormone in the body that drops when we sleep, it’s suspected that disrupting the precise ecosystem of gut bacteria could alter sleep patterns as well.
In fact, fluctuations in gut microbes are tied to circadian rhythm signals that could lead to weight gain, researchers concluded in a 2015 Cell Host & Microbe paper. When researchers disturbed the structure and function of rats’ gut microbes and their sleep cycles and fed them high-fat diets, the result was obese rats. Rodents fed high-fat diets that were subjected to the same interruptions in their circadian rhythms but whose gut bacteria weren’t disturbed didn’t show the same gains in weight.
Altered gut microbes and sleep/wake cycles might have a serious impact on health, according to a 2014 study published in PLOS1 that found that when rats were fed a high-sugar and high-fat diet had their sleep and wake times switched, their gut bacteria changed, causing them to be more susceptible to issues such as obesity and inflammatory bowel disease.
3. The More Exhausted We Are, The Less Fruits and Vegetables We Consume.
The previously mentioned study finding that people eschew fruits and vegetables when they’re tired wasn’t an anomaly — a study published in the January issue of the Journal of Clinical Sleep Medicine found that people whose diets are low in fiber and high in saturated fat slept more lightly and tended to wake more during the night than people who ate higher-fiber diets.
Researchers also found that when nutritionists made participants high-protein meals low in saturated fat, people fell asleep in 17 minutes, whereas when they chose their own less healthful meals, it was 29 minutes before they drifted off. The study authors wrote that they hope diet interventions might prove effective in the future for treating sleep disorders.
Consuming high amounts of fat and sugar and low amounts of fiber for just one day affected sleep quality of participants in a 2013 study published in the journal Appetite. What’s more, pictures of unhealthy food such as pepperoni pizza triggered more brain activity in the sleep deprived than when they were shown pictures of fruits, vegetables and oatmeal.
That pizza and candy generated more neural excitement than oatmeal did probably doesn’t sound that surprising, but the results did indicate that people who’d gotten adequate amounts of sleep were more able to resist the temptation of terrible foods, according to the paper published in Nature in 2013. The authors concluded that sleep deprivation, therefore, might reasonably contribute to obesity. In addition, they reported that study participants ate more and higher amounts of fat than people who’d gotten nine hours of sleep, researchers also found.
4. When Our Sleep Patterns Are Off, So Are Our Eating Patterns.
People appear to be drawn to high-fat foods the day after they’re deprived of adequate sleep, concluded the authors of a 2015 paper published in Scientific Reports.
University of Pennsylvania researchers looking at how sleep deprivation affects activity in the brain noted in that subjects who were kept awake consumed 1,000 calories overnight, in addition to the normal range of calories they ate during the day. The sleep-restricted group, however, tended to get more of those daytime calories from fat compared to their control group counterparts.
It doesn’t stop there. Researchers at Brigham Young University also found that consistent sleep and wake times appear to correlate with lower amounts of body fat in a study published in 2013. Subjects who had more than 90-minute variations in their sleep and wake times had higher body fat composition than those whose sleep and wake time variations didn’t span more than an hour. Those with the lowest body fat were those who got between eight and eight-and-a-half hours of sleep per night.
One more for good measure: Researchers in another study found that late sleepers ate more at dinner after shorter (less than seven hours) sleep, according to the small study of 52 women published in Obesity in 2011. They also slept less overall and were more likely to consume fast food and soda and less likely to eat healthy foods.
5. Yes, Sleep-Eating is a Real Disorder — And Can Be Quite Dangerous.
Researchers are still trying to understand why sleep-eating — also known as a sleep-related eating disorder in which, you guessed it, people eat while asleep and have no memory of it after waking — happens and how to treat it.
The parasomnia is more common among women but affects 1 to 3 percent of the population. It’s much more prevalent among people with eating disorders; 10 to 15 percent of people with eating disorders also have problems with sleep-eating. Peanut butter is a fave among sleep eaters, but some people ingest bizarre, inedible and dangerous items such as uncooked rice or cleaning products. The problem often goes undetected, and sleep eaters tend to have other sleep issues such as sleep apnea, restless leg syndrome or sleepwalking.
Common reasons for sleep-eating include a traumatic event such as a death in the family or taking new medications such as zolpidiem (generic Ambien). Consult a doctor if you’re dieting, as changes in diet also can prompt sleep eating, too. In addition to helping pack on the pounds, the disorder can cause be quite dangerous, causing someone to choke on thick foods or cut or burn themselves during somnambular snack preparation.
6. Night-Eating is Also a Thing.
Not to be confused with sleep-eating, this condition, which is similar to binge eating, could affect as many as 1.5 percent of Americans. It’s thought to be caused by delayed circadian rhythms that make people eat most of their food at night.
A study that appeared in the journal Appetite in March found that severe night-eating syndrome (NES) appears to have a strong correlation with people who have a food addiction, and both conditions in which sufferers tend to have high BMIs and disordered eating patterns. The higher people scored on questionnaires to determine NES severity, in fact, the more likely they were to have a food addiction, to be depressed and report poorer quality sleep.
A 2012 study also found that people with moderate or more severe NES reported significantly lower sleep quality in addition to depressed moods that tend to worsen in the evening.
7. Sleeping in on the Weekends Makes Some People Crave Sugary Drinks
A study published in the Journal of Pediatric Psychology in March suggests that regular sleep and wake times ups the urge to consume sugary beverages. Obese adolescents who stayed up later and slept in later on weekends compared with weekdays drank more sugar-sweetened beverages, especially the boys, and were more likely to be preoccupied with food. In their conclusion, the authors wrote that sleep regularity is an important variable contributing to how much participants eat and drink and should be considered in future weight-loss treatment strategies.
Short sleep (less than seven hours) also seemed to increased the number of calories people consumed from soft drinks, according to research from the University of Alabama at Birmingham released in 2015. Researchers surveyed 28,000 subjects to find out how much secondary eating and drinking (eating or drinking while doing something else) they engaged in while watching TV. Compared with people who got between seven and eight hours of sleep, the short sleepers spent an extra 31.28 minutes a day “secondary drinking,” or drinking beverages other than water, such as sugar-sweetened beverages.
8. Sleep Affects How We Lose Weight
At least, that was the surprising finding of a small 2010 study from the Annals of Internal Medicine. They observed that people on diets lost more lean body mass and less fat when they were sleep-deprived.
In the study, participants lost the same amount of weight but the ones who only slept five-and-a-half hours nightly for a two-week period lost a quarter of their weight in fat and decreased their fat-free body mass by 60 percent. Those who’d slept for eight-and-a-half hours a night, however, lost twice as much fat.
Researchers speculated that when calories are restricted part of the work of maintaining lean body mass happens when we’re asleep, so getting too little sleep might compromise the preservation process.
9. What We Eat Defines Our Dreams. Maybe.
The jury is still out on this, but anecdotally, there are a few types of foods suspected to cause nightmares. An informal 2005 study by the British Cheese Board, for instance, supposedly found that Stilton cheese inspired crazy, vivid dreams and cheddar was said to prompt REM reveries involving of celebrities. That study, however, was only reported on by The Daily Mail.
Still, it appears that even with scant scientific evidence to encourage a link, many people believe that there is one. Forty-seven percent of respondents in a 2015 study said that eating late inspired disturbing dreams, and for whatever reason, cheese, milk and ice cream were the only “statistically significant” foods associated with “bizarre” dreams. Vegetables scored the lowest, which makes sense because who eats carrots as a midnight snack?
One theory holds that spicy foods might cause heartburn and make you toss and turn more, so you’re more likely to wake up frequently and remember bad dreams. Low blood sugar from going to bed hungry is also suspected to possibly increase the likelihood of nightmares. But, again, there’s little scientific evidence to back any of this up.