This essay appears in today’s edition of the Fortune Brainstorm Health Daily. Get it delivered straight to your inbox.

We hear it every Thanksgiving: the turkey on the table, loaded with l-tryptophan, will zonk us out. And there is some truth to that, though the other ingredients of this great American tradition—a giant meal, an inundation of family, a frantic cleaning of a home in anticipation of an inundation of family—may exhaust you as well.

Chemically, the sleep connection comes from tryp’s role in producing serotonin, a neurotransmitter that regulates mood—and serotonin, in turn, is critical for the synthesis of melatonin, a hormone involved in the sleep cycle. As for the mystical Morpheus-drawing quality of the average roasted turkey, one should put that in perspective: There’s plenty of tryp in other poultry, too—plus beef, pork, soy, nuts, and much else—and we barely notice it. (There’s also a freakish amount of the stuff in sea lion kidneys—a food popular among some native Alaskans.)

But tryptophan, one of nine essential amino acids for humans (which the body doesn’t make on its own and therefore have to be obtained from our diets), has some other funky properties beyond the sleep thing. There’s some compelling evidence, for instance, to suggest that tryp might be involved in carbohydrate-craving and the difficulty of keeping weight off. Other studies, meanwhile, are examining tryp’s potential efficacy as an antifungal agent; and as a prognostic indicator in patients with brain cancer (as seen by increased uptake of the amino acid on a PET scan). And a variety of studies are looking at what role the breakdown of tryptophan may play in aging and age-related diseases.

Scientists have been investigating tryptophan-restricted diets for years, mostly in an effort to see what neurological effects they might have. But, for what it’s worth, several studies have shown a correlation between consuming less tryptophan and living longer.

So maybe eat a little less turkey on Thursday. If you’re still hungry, you can always fill up on cranberry sauce. Now, that’s one healthy berry!

I’m off for Thanksgiving and a sleep-restoring Friday. So Brainstorm Health Daily will be back on Monday. In the meantime, you can find an archive of essays here—and please share our subscriber link with anyone you think might enjoy this newsletter.