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Ask a Doctor: Why do I get sleepy in the afternoon after eating lunch?

The most likely culprit is your circadian rhythm, but what you eat may also play a role

AAD: tired after lunch (Chelsea Conrad/The Washington Post)

Lydia Kang is an internal medicine physician at Nebraska Medicine in Omaha and the co-author of “Quackery: A Brief History of the Worst Ways to Cure Everything.”

Q: I always feel sleepy in the afternoon after I eat my lunch. Why does this keep happening, and is there anything I can do to prevent it?

A: Feeling sluggish after lunch is very common. The “afternoon dip,” as it’s sometimes called, refers to those groggy hours between 2 and 5 p.m., when your eyelids droop and your concentration becomes as sharp as vanilla pudding.

There can be myriad reasons this happens, including too little sleep at night or medical conditions such as obstructive sleep apnea, anemia and thyroid disorders. If you feel exhausted, check with your health-care provider to make sure all is well.

But if you’re just feeling a dip in energy, the most likely culprit is your circadian rhythm. Our biological clock is more pervasive than you might think: Though people often only associate it with sleep and wake cycles, it’s also linked to our routines for meals and activity. Research in fruit flies, mice and humans has shown genes control clocks in the cells of our tissues — including the skin, the liver and the brain — that work on an oscillating cycle affected by light exposure.

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Studies have also shown that our alertness tends to be lowest at two points in the day: in the morning from around 2 to 7 a.m. and in the afternoon from 2 to 5 p.m. Most of us are asleep during the first dip, but that slump is highly relevant to shift workers. For people who work during the day, the second slump comes right in the middle of that boring meeting or when you might be driving home. (In fact, you’re far more likely to have a car accident after lunch than after breakfast.)

Research on other causes for the afternoon dip have been limited in scope but can give us further clues as to why it happens. After lunch, your circulation shifts to accommodate more blood flow to the digestive system, meaning less blood goes to your brain, which could trigger some tiredness. A tangled web of hormones, molecules and neurotransmitters is also at work.

One of them, orexin, is a neuropeptide in the brain that affects hunger and helps keep us awake. After a meal, when your glucose levels rise, this may inhibit orexin.

A similar phenomenon occurs with tryptophan, an amino acid that can turn into melatonin, a hormone associated with sleep. We’ve all heard those tales about turkey and tryptophan. It turns out the likely issue isn’t all about the turkey; it may also be the carbs.

Research has found that eating a protein-rich meal is not associated with a higher ratio of tryptophan in our blood. But the insulin rise caused by pairing tryptophan with high-glycemic index foods, such as potatoes, white bread and white rice, can lead to a relative influx of it into the brain and make you feel a bit sleepy.

Why? Insulin tells your body to store amino acids — the building blocks of proteins — in your cells. But it doesn’t do the same thing for tryptophan, giving it easier access to your brain.

In other research, tiredness has been associated with fried foods, saturated animal fats and high-calorie meals, while plant-based foods and the Mediterranean diet have been linked to less sleepiness. That being said, none of these studies were large enough to prove causation.

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Based on what we know, it’s a good idea at lunch to load up on veggies, which are rich in fiber and can help regulate your blood sugar. Avoid consuming a large portion of animal protein and fat. Try eating complex carbohydrates such as whole grains and legumes, and veer away from simple carbs, including sugary drinks and white pasta.

Shaving off even small amounts of sleep for just a few days can worsen afternoon grogginess, so it’s important to get a restorative night of rest on a regular basis. A dose of a caffeinated drink early in the afternoon can help but remember that too much can disrupt your sleep and perpetuate the tiredness cycle.

A brisk walk, ideally outside, can give you a boost, as can bright natural or artificial light: One small study found that bright light exposure reduced fatigue after lunch — perhaps the only time a physician will recommend screen time.

If all else fails, a nap can help improve cognitive performance. Just keep it under 30 minutes and early in the afternoon, so it doesn’t mess with your nighttime sleep schedule.

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