You've been looking forward to Thanksgiving dinner all year — turkey, mashed potatoes, cranberry sauce, and pumpkin pie. Mmm-mmm! But after you finish that second helping of turkey with gravy, you start to feel a little sleepy.
As your Uncle George starts to explain why eating turkey makes people so tired, you suddenly feel like curling up in front of the TV and napping until next Thanksgiving. But is gobbling up all that turkey really to blame?
The Usual Suspect: L-tryptophan
Not exactly. Here's why: Turkey meat contains a lot of an amino acid called L-tryptophan (say: el-trip-teh-fan). Amino acids are the "building blocks" for the proteins that make up our muscles and other important parts of our bodies. (L-tryptophan is just one kind of amino acid — there are many different kinds of amino acids in the foods we eat.)
When we eat foods that contain L-tryptophan, this amino acid travels in the blood from the digestive system and later enters the brain. The brain then changes the L-tryptophan into another chemical called serotonin (say: sare-uh-toh-nin). Serotonin calms us down and helps us sleep.
But scientists now know that L-tryptophan can really only make a person tired right away if it is eaten or taken by itself without any amino acids. And the protein in turkey contains plenty of other amino acids!
Blame It On Blood Flow
Most scientists think that there's a different reason why eating a special meal might make you drowsy. Eating a big Thanksgiving dinner causes increased blood flow to the stomach (needed to help digest the meal) and less blood flow to the brain.