Chemical Misconceptions: The Truth About Turkey...

As we get closer to Thanksgiving, I am reminded of an argument I had with a friend years ago as to the contribution of turkey - more specifically, the amino acid L-Tryptophan - on our typical feelings of lethargy and sleepiness after the big Thanksgiving meal.  I wrote this post way back then, and I thought I'd re-post it now (t'is the season).  I would encourage all of you who read it to spread the truth.  When someone blames the poor turkey for your sluggishness, stand up (stagger to your feet) and say, "It's not the turkey!".  Perhaps, together, we can make the world a happier, more informed place!

The Original Post (my new additions are in purple):

OK, I'm getting tired of having to explain this to people every time Thanksgiving rolls around. I'm not sure how these myths get started, or what perpetuates them, but nothing irritates me more than bad science. So I decided to post this to set the record straight.

First, the facts about L-Tryptophan. Tryptophan is an essential amino acid in your diet. That means your body can't make it by itself - you have to eat it. One of the uses of L-Tryptophan is in the production of Serotonin, a neurotransmitter in the brain. Serotonin is partly responsible for creating a relaxed, sleepy effect. So, since meats like turkey contain L-Tryptophan, shouldn't it make you sleepy when you eat lots of turkey?

In short, no. In order to become sleepy from L-Tryptophan, it would have to be the only thing in your stomach, and that means no other proteins present (never mind carbohydrates). Since few people actually eat pure L-Tryptophan, and since turkey meat is almost entirely protein, you can't get the serotonin spike just by eating turkey meat. In addition, the levels of Tryptophan in turkey are not much higher than the levels in other meats.  So what's the real story? Why do we get all befuddled after Thanksgiving dinner?

The real reason lies in the enormous amounts of carbohydrates and other food that we eat on Thanksgiving (or any holiday where food plays a central role). The large amounts of carbs in your belly diverts blood from your brain to your digestive tract, causing you to become sleepy (why do you think that most predators rest after they eat? It's so they can effectively digest.). Your digestive system works best when there is lots of blood supply in the area to cart away nutrients. The decreased blood flow in your brain deprives the brain of glucose, which in turn makes you a bit sleepy. Add to that the effects of alcohol (a depressant), and the glucose/insulin effect, and you've got nap time!  There is a psychological component to this as well.  Since holidays are typically times of relaxation (unless you're a member of a big Italian family that argues a lot, *cough, cough*), and because the most relaxing time of the actual day is usually meal time, your brain is more predisposed to feeling relaxed.  This feeling can persist even after the meal is over.

So, let's stop perpetuating bad science! Next time someone tells you that it's L-Tryptophan that makes you drowsy on Thanksgiving, offer this experiment. Challenge them to skip the turkey and eat only the other stuff and see if they're wide awake afterwards. Now, if you'll excuse me, I have to go eat.