Why do I get a slump in mental energy after eating a meal?
—Pranati Kapadia, via e-mail
Paul Li, lecturer of cognitive science at the University of California, Berkeley, offers an explanation: Falling asleep at your desk after that heaping bowl of pasta? You may be experiencing what people commonly refer to as a “food coma.” Medically known as postprandial somnolence, a food coma isn’t an actual coma but rather a lack of mental energy that people often experience after eating a large meal. Symptoms include drowsiness, lethargy and a lack of motivation. But not to worry—this postmeal phenomenon is harmless and can strike anyone who pigs out on foods loaded with carbohydrates, fats or sugars.
What is the link between eating a big meal and feeling sleepy? The process begins as food hits the stomach and small intestine. Eating stimulates activity in the parasympathetic nervous system, which tells your body to slow down and digest. The more food you consume, the more the parasympathetic nervous system revs up, causing your body to focus the bulk of its energy on digestion.
Although large quantities of any food can cause a food coma, common table sugar, or sucrose, found in desserts tends to be the main culprit. As food breaks down into glucose—the simplest form of sugar, which the body uses for fuel—you will experience a surge in blood sugar. To counter this spike, your body releases the hormone insulin. Insulin helps to mop up the excess glucose in the blood and returns levels to normal. The increase in insulin also causes your brain to produce more serotonin and melatonin—two neurochemicals that can leave you feeling drowsy. Luckily, this sleepy sensation does not last long—it usually passes after an hour or so.