Chandana Chandra explains: Eating a heavy meal increases blood flow to the stomach required to digest the meal. As a result blood flow to the brain and other organs reduces abruptly. Decreased circulation cuts down supply of oxygen to the brain and it gets ‘tired’ leading to drowsiness. This is called temporary ischaemia of the brain.

The reduced supply of blood may also make a person feel a little uneasy as the supply of oxygen to the heart is also reduced. This minor irritant, however, can be overcome by taking sufficient glucose.

Sometimes, a heavy meal (comprising high protein) may contain a lot of L-trytophan, a type of amino acid. When we eat foods that contain L-trytophan, this amino acid travels from the digestive system to the brain through the circulated blood. Then the brain changes L-trytophan into another chemical called serotonin which calms us down and helps us sleep.

Many scientists also feel that we become sleepy after a large meal because of the reduced level of acidity in the bloodstream. This reduction in acidity is our body’s way of balancing its chemistry ? it occurs as a consequence of extra stomach-acid production. The shift in our blood’s pH (a measure of alkalinity or acidity) is known as the “alkaline tide” which leads to post-lunch and post-dinner drowsiness.

The question was sent by Sumit Kumar from Calcutta-21