With Thanksgiving coming up, you may have heard about the effects of turkey on the brain. The theory goes that turkey contains high levels of tryptophan, which is a key ingredient of serotonin and melatonin; the tryptophan in the turkey boosts serotonin to make you happy, and melatonin to make you feel sleepy. If you've never heard that, I'm a bit surprised. It's practically common knowledge.
Now I hate to burst your bubble, but unfortunately, like many pieces of common knowledge, it's totally wrong (actually, I take it back; I enjoy bursting your bubble). Turkey is not that high in tryptophan, and it doesn't increase the production of serotonin or melatonin any more than pretty much every other meal you eat. You may feel happy and sleepy after Thanksgiving dinner, but it's not the turkey. Like many bits of pseudoscience, this insidious myth is based on some truth, mixed with a little truthiness, along with a dash of misinformation.
Here's the true part: tryptophan in the brain is essential for the production of serotonin (check out my previous posts on serotonin here and here). While it's a gross oversimplification of neurochemistry to say that serotonin makes you happy, that statement tends to be more true than false. Finally, some of that serotonin then gets converted to melatonin. Melatonin, in turn, promotes sleepiness.
However, here's where the myth starts to break down. Yes, it's true that turkey does contain tryptophan, but not a particularly high amount. In fact, all meats contain tryptophan. Tryptophan is just an amino acid—a building block of muscle. Turkey has only marginally more tryptophan than chicken, but not as much as a pork chop. You want a meat that's really high in tryptophan? Try caribou, also known as reindeer (run, run Rudolph!). In fact, some vegetables even have more tryptophan than turkey. Heck, soybeans have twice the tryptophan as turkey. You'd be better off reaching for a slice of tofurkey.
Furthermore, because turkey contains all the other amino acids, this poses a problem for boosting serotonin or melatonin levels in the brain. While tryptophan in the brain may help increase these neurotransmitters, it can't get into the brain when all the other amino acids are floating around in the blood stream. The only way tryptophan is absorbed into the brain is if the blood stream is carrying relatively high levels of tryptophan and low levels of other amino acids. Interestingly, a good way to boost the relative levels of tryptophan in the blood stream, and thus the brain, is to eat carbohydrates. Good thing there's no shortage of mashed potatoes and apple pie at the table. The high-carb foods may have more to do with you feeling good than the turkey. (Sidenote: At this point, particularly if you're a wiseass like me, you might be tempted to say "Aha, the tryptophan in the turkey does get into the brain, but just requires carbs to make it happen." While that may be true, it doesn't make Thanksgiving dinner any more special than any other meal you eat with carbs and meat: bacon and pancakes, chicken and biscuits ... or perhaps for our Scandinavian friends: caribou and ebelskiver.)
If you feel sleepy after Thanksgiving dinner, there are probably dozens of other reasons why. Perhaps you didn't get much sleep the night before when you took the red-eye to Iowa City. Also, the excitement/anxiety of the upcoming meal the meal might have elevated your stress hormones. When those hormones wear off after dinner you might feel tired. You might also be mistaking the feeling of lethargy for sleepiness. Do you really want to go to sleep, or do you just want to lie on the couch and watch TV? It's not surprising that you'd feel lethargic after you spent the entire day watching football, and then just stuffed yourself full of several pounds of food and alcohol. Or maybe you feel tired because you spent the entire day slaving away at a huge, wonderful dinner, while all the other jerks in your family sat around and watched football.
I hope this post armed you with some new knowledge about how the brain works. Thanksgiving, however, is not a time to use your newfound knowledge to berate others and make them feel dumb (do that before or after). Thanksgiving is a time for gathering together and expressing gratitude. So take a moment to focus on what you are thankful for. That's much more likely to make you feel happy, and help you sleep well at night.