The oft-repeated turkey myth stems from the fact that turkey contains the amino acid tryptophan, which forms the basis of brain chemicals that make people tired. But turkey isn't any more sleep-inducing than other foods. In fact, consuming large amounts of carbohydrates and alcohol may be the real cause of a post-Thanksgiving-meal snooze, experts say.

Tryptophan is a component of the brain chemical serotonin, which gets converted into the well-known sleep-inducing hormone melatonin. Poultry and many other foods also contain tryptophan, in similar amounts to that found in turkey. Gram for gram, cheddar cheese actually contains more tryptophan than turkey does. [Thanksgiving Gallery: 8 Fascinating Turkey Facts]

But tryptophan competes with all of the body's other amino acids to enter the brain, through a strict gatekeeper known as the blood-brain barrier. It's the heaps of carbohydrates — the stuffing, potatoes and yams smothered in marshmallows — that are the true problem, according to medical experts. Consuming carbs triggers the release of insulin, which removes most amino acids from the blood, but not tryptophan — that dearth of competitors allows tryptophan to enter the brain and form serotonin and, ultimately, melatonin. (Melatonin can also be produced in the intestine, and a small amount of that may ultimately leak out into the bloodstream and end up in the brain, too.)

Basically, any big meal containing tryptophan and lots of carbohydrates can trigger sleepiness — not just turkey. And on Thanksgiving, many other factors contribute to feelings of tiredness, such as drinking alcohol. The holidays are also a time when people often take a break from their hard work.

When consumed on an empty stomach, tryptophan can lead to serotonin production and more vivid dreams. Tryptophan supplements were a popular sleep aid in the 1980s, but the U.S. Food and Drug Administration banned them in 1991, citing a link with an outbreak of the autoimmune disease eosinophilia-myalgia syndrome — although the link is controversial.

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