Why does turkey make you sleepy?

It's common to take a nap after the huge Thanksgiving feast and blame your drowsiness on the natural sleeping potion chemical tryptophan, found in turkey meat. But does turkey make you sleepy?

Turns out, it's only marginally true. What makes you sleepy after Thanksgiving dinner is any combination of booze, bad conversation and a carbohydrate-heavy meal, but not just the turkey itself.

Tryptophan is an essential amino acid that the body uses to build certain proteins and it can, although somewhat indirectly, induce sleep. The body uses tryptophan in a multi-step process to make serotonin, a neurotransmitter in the brain that helps regulate sleep.

It's true that turkey contains tryptophan, but it's not as loaded with the stuff as you might think: all meat contains comparable levels of the amino acid, so it shouldn't make you any sleepier than, say, bacon. In fact, cheddar cheese, gram for gram, has more. Cheddar isn't the most exciting cheese in the fridge, but no one connects it with sleep. Turkey gets singled out for no other reason than being eaten during the biggest meal of the year.

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In essence, any big meal with any food containing tryptophan can cause sleepiness. The real culprits are all those carbohydrates from potatoes, stuffing, vegetables, bread and pie. The massive intake of carb-heavy calories causes the release of insulin, which triggers muscles to suck up most of the amino acids from the blood except for tryptophan.

With all other amino acids swept out of the bloodstream, tryptophan has no trouble making its way to the brain and influencing the production of serotonin, the real sleep-inducer. Whether its from turkey, ham or any meat or cheese, a cocktail of tryptophan and carbohydrates are the real reason behind the post-dinner zzzzzzzz's.

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Christopher Wanjek is a Live Science contributor and a health and science writer. He is the author of three science books: Spacefarers (2020), Food at Work (2005) and Bad Medicine (2003). His "Food at Work" book and project, concerning workers' health, safety and productivity, was commissioned by the U.N.'s International Labor Organization. For Live Science, Christopher covers public health, nutrition and biology, and he has written extensively for The Washington Post and Sky & Telescope among others, as well as for the NASA Goddard Space Flight Center, where he was a senior writer. Christopher holds a Master of Health degree from Harvard School of Public Health and a degree in journalism from Temple University.