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If you feel sleepy after chowing down, you may wonder what’s going on.

This experience is particularly common after large meals, such as those common on Christmas or Thanksgiving. It’s often referred to colloquially as a food coma. Medically, it’s called postprandial somnolence, which just means sleepiness after eating.

Although there’s limited scientific evidence about how or why this sleepiness occurs, theories exist.

This article tells you what food coma is, the main theories on what causes it, whether it’s dangerous, and how to avoid it.

Keep in mind

Postprandial somnolence — the medical term for food comas, or post-meal sleepiness — isn’t well defined. As many studies on this phenomenon are from the early 2000s, more research is needed.

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What is a food coma?

Postprandial somnolence, or a food coma, is the feeling of tiredness after eating a meal.

It’s also commonly known as the “post-lunch dip,” as many people notice the effects in the early afternoon following lunch (1).

You may experience the following symptoms:

• sleepiness
• lethargy
• physical exhaustion
• low energy levels
• poor concentration

Additionally, although the term contains the word “coma,” you don’t experience a loss of consciousness. Food comas should not be confused with this serious medical condition.

A food coma is the feeling of sleepiness that’s sometimes experienced following a meal. Medically, it’s called postprandial somnolence.

What causes a food coma?

Despite its frequency, food comas aren’t well studied.

Several theories as to the causes of food comas have been challenged or debunked, while others may be plausible scientifically. However, keep in mind that very little recent research is available.

Changes in blood circulation

For a long time, food comas were thought to be triggered by an increase in blood flow to your gut causing a reduction in blood flow to your brain (2).

Yet, this theory has been challenged. Your body is able to maintain blood flow to your brain in many types of stressful situations, such as during exercise, when your muscles require more blood (2).

So, it’s unlikely that blood flow to your intestines diverts enough blood to cause sleepiness.

In fact, an older study suggests that blood flow to your brain may increase following meals (3).

While a more recent, small study found a decrease in blood flow to the brain following lunch, this effect was only seen in people who skipped breakfast. This study also didn’t link the decrease in blood flow to feelings of tiredness (4).

Eating a big meal

People often complain of food comas after eating large or heavy meals.

Studies in fruit flies found that larger meals — particularly those high in protein and salt — resulted in longer post-meal sleep (5).

In a study in men who ate pizza, those who overate reported less energy and more physical tiredness, sleepiness, and lethargy in the 4 hours after eating, while those who ate only until comfortably full had no adverse effects (6).

Another older, small study compared the effects of a light lunch with a heavy lunch that had 3 times the calories on driving and sleepiness. The heavy lunch increased the number of times drivers deviated from their lane, and the effects increased over a 2-hour period (7).

These studies all suggest that large meals may be a trigger for postprandial somnolence.

Meals high in carbs, fat, or protein

Meals rich in carbs, fat, and protein have all been linked to food comas (8).

These macronutrients may promote sleepiness independently through various mechanisms. They may also influence each other.

For example, high carb meals may raise levels of the amino acid tryptophan in your blood, which increases the amount of serotonin — a hormone linked to sleep — in your brain (9, 10).

Furthermore, meals high in protein may also induce sleep if they contain foods with high amounts of tryptophan. These foods include chicken, eggs, cheese, fish, turkey, milk, and tofu (11).

In combination, calorie dense, high fat, high carb meals cause the release of small proteins known as cytokines, which are linked to fatigue (12).

Additionally, meals high in fat or protein may raise levels of peptide YY and the hormone cholecystokinin, both of which may increase feelings of sleepiness (10).

Still, the relationship between foods and released hormones, neuropeptides, inflammatory proteins, and other substances is complex. Determining which, if any, may be responsible for sleepiness requires more research (8).

Effects of eating on your brain and sleep hormones

Another theory links sleepiness to the activation of sleep centers in your brain after eating.

Eating releases various hormones and neurotransmitters that activate parts of your nervous system responsible for digestion (2).

Some brain and nerve pathways involved in digestion overlap with those involved in sleep, fatigue, and drowsiness. So, when these pathways are triggered for digestion, you may begin to feel sleepy (2, 8).

Plus, specific hormones released or reduced around mealtime may affect sleep.

For example, the hormone orexin — which promotes hunger and alertness — is inhibited after you eat (12).

Furthermore, the hormone melatonin is thought to be involved in inducing sleep. It’s generated by your pineal gland and your gut, and production increases after meals (2).

Effects of natural sleep rhythms

Many people experience a food coma as a “post-lunch dip,” where they feel sleepy in the early afternoon (1, 6).

Your body has a natural 24-hour sleep-wake cycle known as the circadian rhythm, or body clock. Research shows that, in addition to the expected sleep phase at night, there’s a smaller sleepy phase (known as the 12-hour harmonic) in the early afternoon (1, 13, 14).

This phase has been observed by dips in work performance and increases in vehicle accidents around 2–4 p.m. (1, 14).

In fact, this natural dip in the circadian rhythm may be one reason for the common practice of an afternoon nap in many cultures around the world (1).

However, eating may still contribute to increased tiredness during sleepy phases of the circadian rhythm.

In fact, an older study noted that meals increased the length of an afternoon nap but didn’t induce it. Similarly, studies simulating night shift workers showed that nighttime meals increase tiredness, compared with not eating (15, 16).

Evolutionary adaptation

Interestingly, postprandial somnolence is seen in many animal species, including simple lifeforms, like nematodes.

This suggests there may be deep-rooted evolutionary reasons for sleepiness after eating.

For example, sleeping after eating may allow your body to store energy for when it’s needed later. It may also allow your brain to process sensory information or learned behaviors about food gathering (17).

Additionally, sleep may simply be the default state that your body reverts to once you eat. This is supported by hunger signals, like acetylcholine and orexin being linked to wakefulness and alertness (17).

Food comas may be caused by evolutionary factors, hormones, your body clock, and heavy meals. Overall, more research is needed.

How long does a food coma last?

No studies have specifically examined how long food comas last.

However, some research notes that the aftereffects have lasted as long as 4 hours after a large meal (7).

This is supported by anecdotal reports of people feeling tired up to a few hours after eating.

Keep in mind that the length and severity of your exhaustion may also be affected by other factors, such as a poor night’s sleep or drinking alcohol (7, 18).

While limited scientific data exists on the duration of food comas, increased sleepiness after eating may last several hours.

Is a food coma harmful? 

Although scientists don’t yet fully understand what causes a food coma, all proposed theories involve your body’s natural physiological responses or processes.

Feeling a little tired after eating is common and no cause for concern — though tiredness can be dangerous in some situations, such as driving or operating heavy machinery (7).

Diabetes risk

Some people worry that tiredness after eating is a sign of diabetes.

When you eat carbs or sugar, your body produces insulin to move the sugar from your bloodstream into your cell, where it’s used for energy.

Yet, people with insulin resistance or diabetes may experience high blood sugar, meaning that the sugar doesn’t reach your cells and leaves them starved of energy. In turn, this may lead to tiredness, as well as thirst and increased urination (19, 20).

Additionally, people with diabetes who take insulin may be more susceptible to low blood sugar if they don’t eat enough carbs. Low blood sugar may also cause sleepiness, as well as dizziness, hunger, irritability, and confusion (21).

If you consistently feel tired after eating and experience other symptoms, like increased thirst, increased urination, fatigue, weight loss, or vision problems, speak with your doctor to determine the cause (22, 23).

Feeling tired after eating is a common physiological response and generally not a cause for concern. If you experience it regularly alongside other symptoms, it may indicate poor blood sugar control that’s worth discussing with a doctor.

How to prevent a food coma 

Although sleepiness after a meal is quite typical, it may be inconvenient when you need to work or study — and even dangerous if you need to drive or perform risky activities.

You can counteract or prevent food comas by following these tips:

• Eat modest portions. Eating large portions is linked to sleepiness, so keep portions moderate and be mindful of your fullness levels (7).
• Choose balanced meals. A study of Brazilian truck drivers found that those who ate a diet low in animal fats, processed foods, and alcohol experienced less sleepiness while driving than those with unhealthy diets (24).
• Limit alcohol intake. Alcohol may induce sleep and disrupt nighttime sleep, causing daytime tiredness. If you drink alcohol with your meal, you may feel sleepier (18).
• Stay hydrated. Dehydration may cause tiredness and impair your mental function, so ensure you drink plenty of fluids — including water, tea, and dairy and nondairy milks — throughout the day (25, 26).
• Get a good night’s sleep. A poor night’s sleep can make the natural dip in energy levels during the afternoon worse, so aim for 7–8 hours sleep per night (7).
• Use bright light. Exposure to bright white light has been found to reduce the effects of the post-lunch dip. Using bright light may be particularly helpful in the office or other work and study environments to prevent sleepiness after meals (14, 27).
• Take a nap. A short 30-minute nap may help restore brain performance, so rather than fighting the effects of a food coma, embracing a short afternoon nap may do the trick (14).

You may be able to prevent or limit food comas by staying hydrated, getting sufficient sleep, limiting alcohol intake, keeping your room brightly lit, taking a restorative nap, or eating balanced meals and moderate portions.

The bottom line

Feeling sleepy after a meal is a common phenomenon known as a food coma.

While research is ongoing, this condition may be caused by sleep-inducing hormones, eating large meals, your body’s internal clock, and evolutionary adaptations.

A food coma isn’t unhealthy, but it may be inconvenient when you need to work or study and potentially dangerous when you’re in high risk situations, like driving.

You can take simple measures to avoid food comas, including limiting portion sizes, choosing more balanced meals, limiting alcohol intake, staying hydrated, getting enough sleep, using bright lights, or just taking a nap.

Just one thing

Try this today: I often feel tired after large, heavy meals, so I try to avoid these and choose smaller, healthier meals when I know I need to stay alert, such as while working or driving.