The Cooking Cardiologist

Feeling sleepy and ready for that nap after your holiday feast?  It is not the L-tryptophan – an amino acid in turkey, which is often blamed for making us feel sleepy.  Serotonin is manufactured in the brain from L-tryptophan and helps to regulate everything from sleep to mood and food intake to pain tolerance.  Low serotonin levels can cause insomnia, depression, food cravings, increased sensitivity to pain and aggressive behavior.  Ironically, eating a protein-rich meal, like turkey, lowers brain serotonin levels while eating carbohydrate-rich foods have the opposite effect.

L-tryptophan can really only make a person tired right away if it is eaten or taken by itself without any other amino acids.  Amino acids have to compete for entry into the brain.  Since L-tryptophan is a relatively large amino acid, only a small amount of it gets through the blood-brain barrier, so serotonin levels do not rise very much.  And turkey contains plenty of other amino acids to compete with L-tryptophan to get across the blood-brain barrier. 

Instead of blaming the turkey, the reason you may feel sleepy after your holiday feast is because of all the carbohydrates you ate.  Carbohydrates found in foods like bread, yams, potatoes, pie and other yummy desserts make us feel sleepy when we overindulge.  Carbohydrate-rich meals trigger the release of insulin from the pancreas.  This hormone causes most amino acids floating in the blood to be absorbed into the body’s cells, not the brain. All amino acids are taken up except L-tryptophan, which remains in the bloodstream at relatively high levels.  With the competing amino acids removed, L-tryptophan can freely enter the brain, causing serotonin levels to rise.  The high serotonin levels, in turn, increase feelings of drowsiness.

So that’s why you feel sleepy after that feast! To keep your energy up as you enjoy the coming holidays, try following some of my holiday tips – they aren’t just for Thanksgiving.