With Thanksgiving just one day away, you and your family are probably already deep into preparations for a feast of turkey, mashed potatoes, stuffing, cranberry sauce and all the fixings.

If you’ll be sitting down to dinner with a big crowd tomorrow, chances are good that you’ll hear at least one mention of how eating too much turkey will make you sleepy, an anecdote you probably recall hearing at countless Thanksgiving feasts in the past. Evidence of this may occur when one or more family members fall asleep after the big meal.

People who are about to give an important presentation or perform for an audience are also sometimes told to eat turkey in an effort to calm nerves. But is the notion really true, or have claims of the sleep-inducing effects of turkey been exaggerated over the years?

Turkey Contains Tryptophan, but it’s Far From Alone

According to scientists, the myth isn’t true. The idea itself comes from the fact that tryptophan, an amino acid included in brain chemicals that create a feeling of sleepiness, is found in turkey. However, it’s no more prevalent in turkey than it is in plenty of other meats, such as pork, that you might eat any other day of the year. Instead, researchers believe that the main reason for sleepiness as your Thanksgiving celebrations wear along is a combination of large quantities of carbohydrates and alcohol, not to mention the exhausting stress that often comes along with holiday preparations.

Tryptophan is just one of the chemical components included in serotonin, the brain chemical largely responsible for feelings of happiness and well-being. The body converts serotonin into melatonin, the hormone responsible for inducing sleep. Just like turkey and pork, chicken contains plenty of tryptophan, and cheddar cheese contains even more tryptophan per pound than these meats.

Carbs and Alcohol: The Real Culprit

In order for tryptophan to actually make you sleepy, it needs to enter through the blood-brain barrier. This isn’t automatic since many other amino acids are trying to enter the brain as well.

However, once plenty of carbohydrates are introduced to the body (via foods like cranberry sauce, potatoes, yams, pies, etc.), it’s much easier for tryptophan to cross the blood-brain barrier. This is because consuming carbs causes the body to release insulin, removing most amino acids from the blood stream except for tryptophan. Without other amino acids for tryptophan to compete against, it passes through the blood-brain barrier in droves and is subsequently converted to melatonin.

As a result, any meal containing tryptophan (in other words, just about any meal containing meat or cheese) and carbohydrates (and remember, most holiday meals include at least one high-carb starch like pasta or potatoes) will bring on feelings of sleepiness. Add to this the alcohol that commonly consumed before, during and after holiday meals, and you have the perfect recipe for a drowsy evening and an early bed time.

The Bottom Line

There’s nothing special about turkey in particular that causes sleepiness. In fact, the tiredness-inducing amino acid in turkey, tryptophan, is found in plenty of other meats, cheeses and more. When tryptophan is combined with a large quantity of carbohydrates, the tryptophan is able to enter the brain much more easily, making you sleepy.