Everyday Explained: Why do you feel sleepy after a heavy lunch? Here’s what happens inside your body

From a full stomach to heavy eyelids, here’s why eating a heavy lunch can make you feel drowsy and sleepy.

A heavy lunch can often be followed by sudden sleepiness, making it hard to stay focused through the afternoon. But why does this happen? In this edition of Everyday Explained, we spoke to Dr Eileen Canday, Head of the Department of Nutrition and Dietetics at Sir HN Reliance Foundation Hospital, to understand what causes post-lunch drowsiness and why a heavy meal can leave you feeling unusually tired.

Why does your body feel sleepy after a big meal?

Dr Eileen highlighted that the drowsiness that people get after having meals is known as Postprandial Somnolence. “When people have taken their meal, the body tends to go into resting mode or the process of digestion. There can be a number of reasons behind making the body feel sleepy, which include signals from the gut, hormonal factors, nutrient flow in the blood, activation of the parasympathetic nervous system, etc,” explained Dr Eileen.

The drowsiness that people get after having meals is known by the term Postprandial Somnolence. (Unsplash)

Such drowsiness happens after one or two hours of having food, especially after consuming heavy meals. Factors like lack of proper night sleep, circadian rhythms, alcohol, dehydration, and sedative medications might make the situation worse.

According to Dr Eileen, the size of the meal is not everything in this case. Blood glucose level also plays a big part. Meals containing high levels of refined carbohydrates cause a sudden rise in glucose levels in the body; then insulin takes over and causes glucose levels to fall suddenly. This can make an individual feel excessively sleepy due to a glucose-insulin imbalance. This phenomenon is called reactive hypoglycemia. Thus, apart from overeating being a factor in sleepiness, glucose-insulin dynamics play a bigger role.

Other reasons for sleepiness post-meal

Dr Eileen highlighted that sleepiness alone cannot indicate hypoglycaemia or diabetes; clinical investigations should be carried out to prove that.

Meals containing high levels of refined carbs and sugar, like white rice, pastries, and sugary drinks, cause sudden spikes and falls in blood sugar.

Fatty meals contain too much fat, which causes delayed gastric emptying and increased metabolic activity.

Large protein-rich meals increase tryptophan production, which helps to synthesise melatonin and serotonin.

Alcohol-containing meals taken during lunch.

A healthy combination of foods for long-lasting alertness consists of moderate amounts of grains, protein, and fats.

A healthy combination of foods for long-lasting alertness consists of moderate amounts of grains, protein, and fats. (Unsplash)

According to Dr Eileen, fatigue after eating a big meal is a usual situation. However, if the symptoms of fatigue are serious and appear after each meal regardless of the amount of food eaten or occur together with increased thirst, unusual weight gain or loss, blurred vision, or inability to focus, then it may indicate that there are some problems related to either insulin resistance or type 2 diabetes. There might also be some thyroid malfunction or an undetected sleep disorder hidden behind such food-induced fatigue.

Note to readers: This article is for informational purposes only and not a substitute for professional medical advice. Always seek the advice of your doctor with any questions about a medical condition.