When You Eat Directly Affects Your Circadian Rhythm and Sleep Quality—Here’s How

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If getting a solid eight hours of sleep a night doesn't come easily to you—and unfortunately, that's very much the case for 70 million Americans—you're probably at least vaguely aware of the connection between food and slumber. (A cup of coffee in the late afternoon could spell trouble, not zzzs.)

But it's not just what you eat that affects sleep; when you eat matters, too. According to scientific research, mealtimes directly affect the body's circadian rhythm, aka the natural physical, mental, and behavioral changes that follow a 24-hour cycle. This connection affects health in both short- and long-term ways. Here, three experts explain the connection between mealtime and sleep, breaking down why exactly it's so important. Plus, they give tips on how to use it to your advantage—even when you're traveling or if you work the night shift.

Experts In This Article
  • Allison Brager, PhD, neuroscientist and author
  • Rebecca Robbins, PhD, assistant professor in medicine at Harvard Medical School and associate scientist at the Brigham and Women’s Hospital
  • Sophie Bostock, PhD, sleep specialist and member of the American Academy of Sleep Medicine and the British Sleep Society

How mealtime affects circadian rhythm

Before we get into the connection between mealtime and sleep, it's helpful to know why exactly circadian rhythm is important in the first place. "Our circadian rhythm is the 24 hour rhythm of activity which is hard-wired into every cell in the body. This helps all our internal systems—such as appetite, metabolism, cardiovascular system, body temperature, and immune function—run in sync with each other," says Sophie Bostock, PhD, also widely known as The Sleep Scientist. "It enables the right things to get to the right places at the right time."

Dr. Bostock explains that the brain relies on signals from the outside world to keep the body clock in sync with the environment, which is how it operates best. "The strongest signal is light, which helps to drive activity and alertness via a master clock in the brain," she says. This is why the majority of society is set up to, for the most part, function during daylight hours and sleep at night.

When we eat, she adds, also affects circadian rhythm. "[Eating] signals to the clocks in the liver, heart, muscles, and kidneys that it's time to get to work," she says. In other words, consuming food alerts the body that it's time to work, not rest. So eating close to when you plan to go to sleep signals to the body that it actually shouldn't be winding down; it needs to stay up to process the meal.

Maj. Allison Brager, PhD, a neuroscientist in the U.S. Army and sleep specialist for Molecule, says this signal doesn't just affect health in the short-term (like how great or not you'll sleep that same night). When mealtimes aren't consistent, the effect can impact long-term health, too. "The [biological] clock exists to predict when to react, eat, drink, mate, and essentially survive. If the clock has predictability with predictable mealtimes, life is good. We know this to be true because the number one threat of night shift work is weight gain, obesity, and metabolic disorders such as type 2 diabetes," Dr. Brager says.

"Consistency is very important to the body, and that includes sleep times and mealtimes." —Rebecca Robbins, PhD, sleep researcher

Harvard-trained sleep researcher Rebecca Robbins, PhD, who is a sleep scientist at Brigham and Women’s Hospital, agrees. "Consistency is very important to the body, and that includes sleep times and mealtimes," she says, adding that routinely waking up and going to bed at the same helps keep circadian rhythm on track, and so does eating breakfast, lunch, and dinner roughly at the same time. Working against the clock could lead to chronic health problems, such as the ones Dr. Brager mentioned.

With this in mind, the sleep experts say there are several ways you can use mealtime to keep your circadian rhythm steady, even if you work untraditional hours or are traveling (and thus may be less likely to stick to consistent mealtimes).

4 tips for how to optimize the connection between mealtime and sleep in your life

1. Be consistent with mealtimes

The most straightforward way to use this connection to your advantage is by eating your meals at roughly the same time each day. "We know that the body expects to use certain kinds of fuel at specific times of the day. Your body is best at digesting food and drinks when you are active and light is present," reads a scientific article published in the Journal of Biological Rhythms. "[This means that] eating and drinking when your body expects you to sleep and rest, and it is dark, can disrupt this system and compromise metabolism. In contrast, a consistent daily cycle of eating and fasting may nurture a healthy circadian clock and optimize metabolism." You can put that intel directly to use by eating your meals at regular times, ideally when it's still light outside.

2. Allow the body time to rest (and not digest) before bedtime

Another way to hack your mealtimes for better sleep is to allow your body plenty of time to rest, says Dr. Robbins. Ideally this means not eating at least two hours before bed.

3. For shift workers, eat more meals of a smaller portion—and plan ahead

If you work a night shift, eating your meals while it's still light out may not work for you, so Dr. Bostock says it's better to eat several small meals throughout the day instead of three bigger meals within a 10- to 12-hour window. The body tends to crave sugar and fat more when it's tired, so eating several small meals of protein- and fiber-rich foods helps mitigate this while still allowing plenty of time to rest while you sleep, she says.

Dr. Brager acknowledges that making nutrient-rich food choices and eating at consistent times definitely tends to be trickier when you work untraditional hours, which is why she recommends meal prepping and planning in advance what you'll eat and snack on. "The key is still finding a sense of normalcy and consistency," Dr. Robbins says. This includes when you eat and what time you go to bed and wake up. She also strongly recommends investing in some blackout curtains to "trick" your body into thinking that it's nighttime when you head to bed since light is the strongest signal to the brain in terms of circadian rhythm.

4. Get on a regular sleep-and-meal schedule as soon as possible when traveling

If you're traveling somewhere in a new time zone, Dr. Bostock recommends trying to adjust as quickly as you can in terms of when you eat and sleep. "Airlines will tend to serve food when it is convenient for the crew, rather than necessarily when it's best for your body clock, so it may help to take your own food supplies with you," she says. But even with these tips in mind, she says your first couple of nights in your new locale still may not be perfect in terms of sleep. "The body's clocks only adjust by about an hour every 24 hours, so you cannot suddenly adjust," she says.

While many factors contribute to our sleep quality—like stress, exercise, work schedules, caretaking commitments, and screen time to name just a few—if you have trouble sleeping and tend to have erratic (or late-night) mealtimes, it's certainly worth evaluating. As the experts have so clearly pointed out, working against the body's natural circadian rhythm doesn't just negatively impact sleep, but also overall health. With that in mind, consistent mealtimes just may make all the difference for you. That, and some really good blackout shades.

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