Will this Thanksgiving staple put you to sleep, or can we bust this myth once and for all?

We’ve all heard it before, right? Comments that the high content of tryptophan in turkey makes people sleepy are as plentiful as the stuffing grandma makes for the big Thanksgiving feast every year. However contrary to popular belief, consuming turkey likely isn’t the main culprit of your post-meal coma.

The origin of turkey’s supposed sleep-inducing powers stems from the fact that the amino acid tryptophan is actually a precursor to serotonin, a neurotransmitter responsible for numerous processes in the body. One process is the production of melatonin, which is a hormone that regulates sleep-wake cycles. In fact, melatonin supplements are often used to treat insomnia and other sleep issues.

Thus springs forth the idea that turkey makes you tired–but in reality, the tryptophan amounts we see in turkey really aren’t that remarkable. While turkey contains approximately 114 mg of tryptophan per ounce, we find that mozzarella cheese has 160 mg/oz, and soybeans have 161 mg/oz. Even chicken has a slightly higher tryptophan content than turkey (118 mg/oz).

Rather than high tryptophan content alone, research has shown that the more likely cause of your post-meal passout are those pesky carbohydrates. Tryptophan is the largest amino acid found in the body, and this makes it difficult to cross the blood-brain barrier. But consuming large amounts of carbs in combination with any tryptophan-rich foods will release insulin and allow tryptophan to cross this barrier and increase serotonin levels.

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So when you’ve settled into the couch after enjoying arguably the year’s best meal and feel yourself starting to doze off, blame that second helping of mashed potatoes.