Why do we feel sleepy after eating?

   After eating – particularly sugary foods – the pancreas produces insulin, which converts these sugars circulating in the bloodstream into the stored forms within cells.

The increased level of insulin triggers the movement and action of tryptophan, which is an essential amino acid, within the brain. Essential amino acids can’t be made by the body, and must be taken in from our diet.

Once in the brain, it leads to increased production of serotonin, a neurotransmitter that passes electrical signals between connecting neurons. Around 90 per cent of the body’s serotonin is found in the abdomen, where it regulates intestinal movements.

The remaining ten per cent is located in the brain. Serotonin has several functions, including control of mood and slumber; it has also been linked to depression and feelings of intimacy.

Increased levels of serotonin simulated following a sugary meal can thus lead to you feeling sleepy. But other factors may contribute to drowsiness after a meal.

Particularly large meals take time to digest, meaning blood may be diverted away from other body areas to help with this. Further, if you are dehydrated during or after eating, this may exacerbate your lethargy.