Med thumb turkey riding 2

Seinfeld laid bare a lot of truths — about human nature, social mores and barriers to napping under your desk. But, the sitcom got at least one thing wrong, when it showed Jerry and George lull a woman to sleep with turkey and boxed wine. The myth of turkey as a sleep aid was busted a long ago.

Do we feel lethargic after shoveling thyme-flavored everything into our mouths? Sure, but blame it on the excess, not the tryptophan.

Why would tryptophan make us tired?

Tryptophan is an essential amino acid, which means it’s something we need but cannot produce ourselves. So we get it from outside sources (i.e., our diets). And while we don’t actually make tryptophan, we do use it to make other important chemicals, including serotonin, a calming neurotransmitter involved in mood regulation.

In turn, we convert some serotonin into melatonin, the sleep-regulating hormone released by the pineal gland in response to darkness. So, with a couple of degrees of separation, the tryptophan-sleep connection holds true.

But isn’t turkey bursting with tryptophan?

The notoriously dim-witted bird does indeed contain tryptophan, but no more than other protein sources. Chicken is on par (roughly 350 mgs of trypto per 115 grams of protein, according to the BMJ); pork and cheese pack even more.

Postprandial drowsiness probably has more to do with feasting on combos of protein and carbs. In this scenario, carbo-loading spurs the release of insulin to break down starchy sugars; this, in turn, stimulates the absorption of other amino acids (but not tryptophan) into the muscles. As a result, a higher concentration of tryptophan ends up in the blood and, eventually, reaches the cerebrospinal fluid.

But a countermeasure may also be at play: Some evidence suggests tryptophan induces sleepiness only if taken on an empty stomach and without other amino acids. As we know, your average turkey dinner both fills bellies and supplies countless other amino acids.

So Seinfeld got it wrong?

Not entirely. The other half of the Jerry’s plan — red wine — surely sends a lot of people to bed. The snoozy effects of alcohol, however, don’t necessarily last. Imbibing can make it easier to nod off but harder to stay asleep.

I’m telling you, that big plate of turkey knocks me out every time.

No one’s calling you a liar. But it’s simply more likely that we slip into food comas because we’ve eaten to the point of bursting. Feeling full triggers the “rest-and-digest” system, technically called the parasympathetic nervous system. During this time, our body puts resources toward automatic processes (i.e., digestion) rather than energy-expending muscle movement.

Don’t feel bad. This is a completely natural process and it’s eminently easy to overeat on Thanksgiving. Even modest servings of everything on the table, taken together, will tip the scales toward gluttony. And we know you’re not being modest. But again, that’s okay — it’s Thanksgiving.