Forks no longer clang against plates. Conversation lulls. Chairs scrape against the floor as family members make their way from kitchen table to Lazy-Z-Boy. The Thanksgiving feast is over. Now, eyelids drowse. Everyone starts to fall asleep, wine glasses are half full, football commentators hum in the background, crumbs stuck to mustaches flutter in the rhythm of each hot, heavy breath.

Is this your Thanksgiving meal aftermath? Maybe your astute, know-it-all cousin points out that tryptophan, present in turkey (and many other foods) is causing everyone to fall asleep by 6pm.

You can tell them that’s just a myth. Tryptophan isn’t the reason your living room looks like an kindergarten nap time, it’s all the other stuff you’re eating alongside it.

What is Tryptophan?

It’s an amino acid. Amino acids form the building blocks of protein: the main structural and functional compound in the body. While non-athletes might not have heard about amino acids, fitness buffs have probably tried to upgrade their regular protein shakes with big doses of BCAAs (branched chain amino acids) or EAAs (essential amino acids). Both these are specific amino acids found in protein that are necessary for muscle-building and great supplements for recovery.

BCAAs are non-essential amino acids, meaning they’re not essential to consume through supplementation; the body can make them itself from other amino acids in the diet. Tryptophan, on the other hand, is one of nine essential amino acids, meaning it cannot be produced by the body and must be obtained directly through food.

Tryptophan plays a part in some vital, bodily processes. It helps regulate nitrogen balance in adults and growth in infants, and also is important for production of creating niacin–essential for creating serotonin. Serotonin is a neurotransmitter associated with sleep and melatonin levels.

This is where the villainization of turkey comes in. But tryptophan isn’t just in turkey; it’s also in other high-protein foods. In fact, many foods have more tryptophan than turkey: seeds, cheese and soybeans.

You’re Tired Because

You overate.

Yes: tryptophan can make you drowsy. But the other foods that contain tryptophan in high amounts don’t get the same bad rap as turkey–so what’s causing the sleepiness?

Really it’s mixing tryptophan-rich turkey with other carbohydrates–like, say, mashed potatoes and stuffing and bread and pie–that is to blame.

Consuming carbs triggers insulin release, which causes uptake of other types of amino acid into the muscles (but not tryptophan). This means that tryptophan levels are higher than usual, especially relative to other amino acids. Normally amino acids compete with one another for uptake into the brain, but when tryptophan is present at higher-than usual amounts, more of it gets in.

Without competition, the floodgates open, allowing more and more tryptophan to enter the brain. From there it’s used to produce serotonin and eventually, melatonin.Fernstrom1971 Any big meal containing tryptophan and lots of carbohydrates can induce drowsiness. And of course other factors, like drinking alcohol, can also play a role in that sleepiness.

Even if you ate a large meal without any tryptophan, you’ll likely still be tired–especially if it’s rich in carbohydrates.Lyons1988,Wurtman2003,Afaghi2007 Large portions of food force the body to digest, which requires significant energy use. You’ll get the signal from your brain to chill out while your gut kicks into overdrive. This feeling is likely unavoidable, because the parasympathetic nervous system (responsible for telling your heart to beat and your lungs to breathe) automatically triggers this process, informally known as “rest and digest.”

Tryptophan may play a role in post-meal tiredness, but it’s largely everything else you ate putting you into a food coma.