Well, we’re closing in on Thanksgiving, where many people will eat too much and slump down into the couch feeling good and feeling sleepy. I’ve heard talk time-and-again about how eating all that turkey causes you to feel sleepy because of its high levels of tryptophan. Let’s take a closer look at that…

First off, tryptophan is just a biological precursor used to derive the neurotransmitter serotonin (which gives you that “feel good” feeling) and the hormone melatonin (which helps regulate your circadian rhythms…and cause drowsiness because of that).

So, why does the body derive these from tryptophan? Why not produce and/or take them straight up? Well, the body has this little thing known as the blood-brain barrier, which protects the brain from chemicals (hormones and such) floating around in the blood. The barrier is difficult to get through…serotonin, melatonin and other similar substances can’t make it through this barrier (which is why taking serotonin orally to get that good [and anti-depressant] feeling out of it doesn’t work because it can’t pass from the blood to the brain to have any effect).

That’s where tryptophan comes in…it can get through this barrier through the use of a transport molecule. But (always a “but,” isn’t there?), there’s a slight problem…these transport molecules are shared with other amino acids. If thiese other (highly abundant) amino acids use up the transport molecules (which they do most of the time), the tryptophan from foods we reach won’t really get to the brain in any significant amounts.

So, what makes our Thanksgiving turkey so special to induce our sleepy, happy feeling? Nothing.

That’s right…nothing. There’s nothing special about the tryptophan in turkey. In fact, mushrooms, lobster, crab, shrimp, soy protein, quail, pork, goat, and even spinach have high levels of tryptophan in them as well (in some cases, much higher than turkey). That’s right…Popeye could have been feeling good because of all that spinach he ate. Could have been. Taken by themselves, the body will only utilize a very low percentage of tryptophan. It needs one other ingredient to make it all work…


Yep, think of all the carbs that go alongside that turkey…stuffing, mashed potatoes, gravy, sweet potatoes, rolls, and lots of pie. These carbohydrates produce insulin, which snatches up a lot of amino acids in the blood…but not tryptophan. This essentially clears the way for tryptophan to have a clean run at the majority of the transport molecules to get through the blood-brain barrier. Thus, allowing the brain to manufacture its natural happy, sleepy drugs.

And that’s a really quick run-down on the subject from someone who’s definitely rusty in his biology, but at least now when you’re lying nearly comatose on your couch after the holiday feeding frenzy, you’ll know. Tryptophan…it’s not just in your turkey, and it doesn’t really affect you until you toss in some carbs.