From Bedtime to Mealtime: Understanding the Sleep-Diet Relationship
Good habits at the dinner table and in the bedroom are a recipe for optimal health.
Poor sleep is associated with worse diet quality, and sleeping less causes people to eat more — and more of the wrong things. Mounting evidence also suggests that what we eat can impact how well we sleep. Tryptophan-rich foods enhance melatonin synthesis and may be one strategy to promote healthy sleep, but overall dietary patterns characterized by an abundance of whole foods and minimal processed foods are also associated with improved sleep quantity and quality. This article will discuss the bi-directional relationship between sleep and diet, explore the mechanisms of sleep-promoting foods, and explain why you might crave junk food when you’re sleep-deprived.
Physical activity, sleep, and diet are key pillars influencing health and longevity.
Assembling a hierarchy of these three would be a difficult task. We have to exercise daily to stay strong and aerobically fit, we have to achieve the optimal amount of sleep (for us) each night to function properly throughout the day, and we have to “eat right” (a term that’s impossible to define) to avoid the diseases that plague modern society and manage our metabolic health.
Depending on whom you ask, you’ll get a different response as to which pillar is most important. “It’s all about diet!” claim the low-carb fanatics. “People just aren’t active like our hunter-gatherer ancestors!” shout the exercise physiologists (guilty). In reality, all of the pillars are necessary and none are sufficient for optimal health.
Furthermore, none of the pillars exist in isolation. Rather, they influence one another.
Eating right and sleeping enough give us energy to engage in regular exercise. Regular exercise promotes a myriad of processes that lead to better sleep and helps regulate appetite and energy intake. Sure, sometimes we can atone for the sins of a suboptimal diet by exercising a bit more, but ultimately, a weak link makes the entire chain useless. Good habits around one pillar promote good habits around the others.
There’s a special reciprocity among health-promoting habits.
Today, we’ll focus on the synergy between diet and sleep — a relationship that’s incredibly complex but endlessly fascinating.
How sleep affects diet
People who sleep less eat worse. A short sleep duration is linked to a greater intake of fat, sugar, and total energy, along with a lower intake of vegetables, fruit, and whole grains.
But these data come from observational studies — making it impossible to derive causation. Does short sleep cause poor dietary habits? Could the poor dietary choices be causing inadequate sleep? Maybe it’s both.
To better understand the direct impact of sleep on what we eat, experimental studies are a useful tool. Deprive people of sleep and measure their food intake and appetite before and after.
Studies like this indicate that when people are limited to 5.5 hours of sleep per night or less, they eat about 400 calories more compared to when they’re well-rested.
Sleep deprivation also changes what we eat: fat and refined carbohydrate intake goes up, protein intake goes down, and snacking increases.
But why do we eat more when we’ve not had enough sleep? This question has puzzled researchers and has resulted in a number of hypotheses. Perhaps less sleep means that our energy expenditure increases, leading to a higher caloric burn and a greater appetite. Maybe more time awake just means there’s more time available to eat — let’s call it “opportunistic snacking.” Perhaps the appetite-regulating hormones leptin and ghrelin play a role.
Research in this area has pointed in a different direction — toward reward valuation.
In short, getting less sleep seems to make food more rewarding — especially salty, sugary, high-fat foods. Sleep deprivation makes us crave energy-dense foods, and these foods simply taste better to a sleep-deprived brain.
Does the opposite hold true? Does sleeping more improve diet quality?
There’s a lot less research in this area, but studies suggest that sleep extension (in people who are short-sleepers) reduces the desire for sweet and salty foods and may reduce people’s intake of carbohydrates and sugar.
How diet affects sleep
Before delving into the specific effects of different foods and nutrients on sleep, let’s get basic.
We’ve all heard of melatonin, the so-called “sleep hormone.” In reality, it does much more, but its primary role is to modulate our sleep-wake cycle.
When it gets dark, our pineal gland releases melatonin, which then sends a signal to the suprachiasmatic nucleus (the SCN, the “master regular” of our body’s circadian rhythm) telling us it’s time to sleep. Melatonin levels are lowest in the morning and throughout the day and rise in the evening.
Serotonin also plays a role in modulating our sleep-wake cycle via several different pathways that we won’t discuss here. Rather, just note that serotonin is involved in the synthesis of melatonin in the body.
Our body makes all of its melatonin from the amino acid tryptophan, which we obtain from our diet (it’s what is known as an essential amino acid — our body can’t produce it). Tryptophan is found in high amounts in beef, lamb, poultry, and dairy, along with seeds, whole grains, and legumes.
After we’ve eaten tryptophan-rich foods and the amino acids have been digested and transported to the circulation, they cross the blood-brain barrier and enter the brain. Here, tryptophan is converted to serotonin, which is then converted to melatonin in a process requiring B vitamins and magnesium. Endogenously produced melatonin is then released into the bloodstream to do its work.
Sleep-promoting foods
Given the previously discussed roles of tryptophan, serotonin, and melatonin in the regulation of sleep, it seems plausible that increasing the availability of any or all of them through the consumption of specific foods could help promote sleep.
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