To Eat, Perchance To Sleep

Name a country and, with the possible exception of Spain, sleep problems appear to be on the rise. More and more people everywhere are reporting less and less sleep and less restful sleep. Not only are they missing the near universally recommended seven hours per night, they’re also having a harder time falling asleep and staying asleep. As sleep takes a dive, medical concern is rising: Studies increasingly link both sleep deprivation and sleep irregularity to a growing host of ills, from motivational blahs to metabolic disorders to cardiovascular mortality.

Sleep is a biological imperative, rhythmically encoded in every cell of the body. The human sleep-wake cycle coordinates all mental and physical processes and how well those processes function. Sleep is essential for cognitive performance, metabolism, immune function, and appetite and hormone regulation, to name a few.

The master timekeeper, tucked into the suprachiasmatic nucleus of the hypothalamus, is closely tied to nature’s cycle of light and darkness. Light is the main cue prompting the SCN to coordinate the rhythm of physiology and behavior, but it’s not the only one. External temperature and physical activity levels have an influence.

So, too, does diet. In fact, diet is one of the stronger synchronizers of the body’s clock mechanisms—a zeitgeber, in the lexicon of science. Irregular or abnormal feeding times, researchers find, can interfere with the effects of environmental cues on the central pacemaker. They can, for example, interrupt the rhythm of melatonin production, the sleep-inducing hormone the brain produces as day darkens into night.

Feeding needs are so timed to daylight that mistimed dietary intake, such as late-night eating, has even been found to alter the genetic machinery of the body clock itself. Feeding signals may have their greatest effect on the pacemaker mechanisms of specific organs of the body—the liver and kidneys, for example.

Over the last two decades, researchers have increasingly incorporated information about the body’s temporal rhythms into nutrition research, developing a field of study known as chrononutrition. One of the clearest findings of chrononutrition is that most people function best—and metabolism itself benefits—when food intake (like other human activity) is aligned with the biological clock, which is synchronized to light cycles.

For most of human history, there was no other way to survive. The agricultural revolution and, later, artificial lighting changed all that. Even in the 21st century, mounting evidence suggests we should be eating most of our calories and certainly our carbohydrates at a midday meal and stopping food consumption before late evening.

Some research indicates that in terms of metabolic and brain health, such time restriction of food intake is more important than the amount of energy consumed at those times. In other words, a calorie is not always a calorie. Studies repeatedly show that shifting energy intake to earlier rather than later in the day not only induces weight loss but also lowers levels of LDL cholesterol, fasting glucose, and insulin resistance.

Even in the unremitting darkness of the human gut, light exerts its pacemaker influence. Gut microorganisms, like other living things, have their activity rhythms timed to light and dark periods, signaled also by melatonin and temperature.

Several studies demonstrate that circadian disruptions in sleep, diet, and eating patterns affect the diurnal dynamics of the microbiome, impairing metabolic function and inflammatory processes, leading to an increased risk of metabolic syndrome. Delayed meal intake, breakfast skipping, and late-night eating have been associated with circadian rhythm disruptions of glucose metabolism, body temperature, and secretion of melatonin and the stress hormone cortisol.

But the timing of meals is not their only influence on circadian competence and sleep. Their contents count, too. There are a number of specific nutrients that influence sleep, by affecting the body clock and other means.

In fact, it may be that the healthful effects of the Mediterranean diet are due, in no small measure, to the contribution it makes to circadian patterns and sleep. The diet, rich in plant-based foods, is also rich in melatonin.

Melatonin is both a hormone that influences circadian rhythm and a powerful antioxidant. It is produced by the brain’s pineal gland, but it is also a component of many fruits and vegetables. Tomatoes, olive oil, red wine, almonds, pine nuts, garlic, cauliflower, lentils, and barley are among them, all components of the Mediterranean diet. Animal-derived food products—meat, fish, eggs—contain only minuscule amounts of the substance.

The melatonin content of even the same food can vary enormously, depending on the variety of plant grown, the time of day it is harvested, and post-harvest processing. Nevertheless, studies show, diet-derived melatonin raises human blood levels of the hormone and is biologically active.

The regular consumption of such foods, researchers believe, can influence both sleep quality and sleep quantity. Apart from the foods themselves, the Mediterranean diet is notable for assigning the bulk of energy consumption to the meal at midday, when circadian rhythms can most accommodate it. No one has yet quantified how many of the health benefits of this diet are due to promoting restorative sleep, but sleep seems to be yet one more pathway through which the diet can lower the risk for such chronic conditions as cancer and cardiometabolic, neurodegenerative, and psychiatric diseases.

The Mediterranean diet provides other nutrients that influence sleep. One is tryptophan, precursor to serotonin. While serotonin itself has a complex effect on sleep, adequate serotonin levels are essential for the production of melatonin in the body. High levels of tryptophan are found in spinach, tomatoes, plums, and walnuts, all foods regularly consumed in the Mediterranean diet. Milk is also rich in tryptophan, and while milk is not regularly consumed as part of this diet—adults in the region generally lose the ability to tolerate lactose unless it undergoes fermentation—it is ingested as cheese.

Omega-3 fatty acids, found in fatty fish and consumed at suboptimal levels in Western diets, also promote melatonin production in the body. Studies link them especially to increased sleep efficiency. While salmon is not native to the Mediterranean, other fatty fishes—tuna, mackerel, and anchovy—are.

Of course, the best source of nutrients is always whole foods. They usually contain many factors that work in synchrony to promote positive effects. But supplements of substances such as melatonin and omega-3 fatty acids are supported by many studies.

Foods to Snooze By

Melatonin-boosting foods

• Tomatoes
• Walnuts
• Grapes
• Tart cherries
• Goji berries
• Fatty fish

Serotonin-boosting foods

• Kiwifruit
• Milk
• Turkey
• Chicken
• Canned tuna

Anti-sleep foods

• Candy
• Caffeinated beverages
• Chocolate
• Salami
• Aged cheese
• Citrus fruit