Postprandial somnolence or food coma

Postprandial somnolence, commonly known as a "food coma," refers to the feeling of drowsiness or fatigue that occurs after eating a meal. Post-meal drowsiness is actually the combined result of several body processes and behaviours.

This phenomenon is especially common in the early afternoon, during what is known as the “post-lunch dip.”

The tendency to feel sleepy after a meal, especially after lunch, is very common—though some people experience it more strongly than others and some people, like me, don’t experience it at all!

This is because I work a lot and both my body and brain are in a high state of alert most of the time.

High-carb foods trigger rapid blood sugar spikes, hormonal shifts, and chemical changes in the brain that promote relaxation and sleep. 

Circadian Rhythms and Sleep Drive: Eating at night aligns with your body's natural internal clock (the circadian rhythm), which naturally promotes rest as bedtime approaches. The longer you have been awake during the day, the higher your sleep drive becomes. 

A number of biological processes contribute to drowsiness following a meal. They include

Circadian rhythms: Circadian rhythms are natural fluctuations in body temperature, hormones, metabolism, and other physiological processes that operate according to a 24-hour clock. The circadian signals that promote wakefulness tend to decrease in the early afternoon, which can lead to sleepiness following lunch. (1)

Sleep drive: The longer you’ve been awake, the more your desire to sleep—known as the sleep drive—grows. Thus, you’re more likely to feel drowsy following an afternoon or evening meal than after breakfast.

Reduced brain activity: Brain activity and cognitive function appears to slow following a meal, which may contribute to sleepiness. (2)

Hormonal changes: Eating promotes a drop in hormones that maintain alertness and a rise in hormones that promote sleepiness, including melatonin and serotonin.

Cytokines: Cytokines are proteins that play an important role in the body’s immune and inflammatory responses—and they have also been linked to feelings of fatigue when the level fluctuates. The concentration of certain cytokines in your body rises after you eat, especially if you’ve consumed a high-calorie meal. (3)

Researchers theorize that postprandial somnolence may serve several possible functions, including allowing the body to dedicate resources to digestion and helping conserve energy.

And the act of eating is not solely responsible for the feelings of drowsiness that sometimes follow a meal. In fact, you may still experience the post-lunch dip even if you skip lunch. However, research indicates that you’re more likely to feel tired after eating some foods than others like

High-fat foods: Meals with foods that are high in fat can induce feelings of fatigue. Moreover, diets that include too much fat can compromise night-time sleep, leading to even more daytime tiredness.

High-carbohydrate foods: A high-carbohydrate meal is more likely to cause you to feel sleepy than a low-carbohydrate meal.

You might have heard that foods containing the amino acid tryptophan, such as turkey, cause sleepiness. Tryptophan is converted in the body to melatonin and serotonin which are both hormones that increase sleepiness. However, tryptophan alone is not to blame for the drowsiness many people feel after big meals. Rather, eating a “heavy” meal with many calories from both fat and carbohydrates is a recipe for postprandial somnolence.

There are several other factors that can cause or intensify sleepiness after meals

Disturbed sleep or sleep deprivation: If you sleep poorly at night, or if you don’t get the amount of sleep you need, post-meal drowsiness tends to be more intense due to increased sleep drive. (4)

High or low blood sugar: Fatigue can be a symptom of both high and low blood sugar levels. People with diabetes are more susceptible to these issues, due to difficult to regulate blood sugar levels which may be caused by taking too much or too little exogenous insulin. High and low blood sugar can also result from diet, alcohol consumption, or changes in physical activity levels.

Iron deficiency: If you have low iron levels, you are at risk of developing restless legs syndrome (RLS), which can compromise your sleep at night and lead to excessive daytime sleepiness.

Alcohol consumption: Alcohol can make you sleepy, and this effect is even more pronounced if you are sleep deprived.

Chronotype: Research suggests that if you are a “lark”—that is, a morning person (5)—you are more likely than “night owls” to experience post-lunchtime sleepiness.

So if you take care of some of these things - like having good sleep during the night, keeping your brain alert by working and not sitting idly during day time, not having very heavy meals full of fats and carbohydrates - you don’t feel that drowsy during the day time.