It’s Thanksgiving and once again a familiar piece of nutritional reasoning is looping through your mind. It goes like this: Turkey is a rich source of the essential amino acid tryptophan, which our bodies need to build certain kinds of proteins. Tryptophan also is a precursor to serotonin, used to make melatonin, a hormone that helps regulate sleep. Therefore, eating a lot of turkey will make me sleepy while watching football.

Despite how perfectly sound each link in that chain of logic may appear, the conclusion is absolutely false.

“Turkey doesn’t make you sleepy,” said Kim Sasso, a registered and licensed dietitian who spoke to a Loyola University Health System press officer.

Yes, it’s true your holiday bird contains tryptophan, but many other foods, including most other meats, contain the amino acid at comparable levels. In fact, the humble soybean and cheddar cheese both contain more tryptophan, gram for gram, than turkey. As Sasso explained, no matter how much turkey you eat, it simply won’t be enough — after breakdown, metabolism, and transfer within your body — to have a real impact on your brain and cause sleepiness after your holiday meal.

So what does make you sleepy on Turkey day?

Eating too much in general, says Sasso, along with “the stressful hustle and bustle of the holiday, travel schedules, alcohol indulgence, and cooking tasks.”

To learn more about tryptophan and turkeys, watch the video from ByteSize Science, sponsored by the American Chemical Society.