If you’re a carnivore, and an American, a serving of perfectly roasted turkey will probably adorn your plate on Thanksgiving day, and fill your sandwiches for the days after.

There is a good chance you’ll hear rumors, news reports or dinner table chit-chat that eating turkey makes you sleepy. “It’s the tryptophan!” they say when the post-feast drowsiness hits. We might have never heard of it if it didn’t get the blame (or thanks) for our holiday naps.

But is tryptophan really the reason we want that afternoon snooze? The truth about tryptophan is that it’s simply an essential amino acid. And think about it, do you take a nap after downing turkey tacos or a turkey wrap the day after the holiday? I didn’t think so. It’s time to cut turkey some slack. In fact, foods like chia seeds and soybeans have more tryptophan than a serving of turkey!

There are nine essential amino acids we consume through a balanced diet. They are the building blocks of protein, which is an essential nutrient for growth that helps us maintain our body’s systems, tissues, and organs and promote restful sleep. Amino acids are also critical for muscle development, maintenance and recovery after hard workouts, making them all the more important for athletes. When you consume any food that has complete proteins, you’re consuming all nine essential amino acids—tryptophan included. 

On Thanksgiving Day, tryptophan intake shouldn’t have any significant impact on your mood, or your energy levels on the run. But there are other factors that might be contributing to how you feel and your ability to get motivated for a long run. Here’s a look at what tryptophan is and how it might affect you.

Food sources of tryptophan

Any dietary source of complete protein (i.e. contains all nine essential amino acids) has tryptophan. Some foods are considered incomplete proteins, meaning they don’t contain all nine essential amino acids, but they may still have some tryptophan.

Complete proteins: meat, poultry, fish, eggs, soybeans (and soy products), dairy, and quinoa

Incomplete proteins (may have varying levels of tryptophan): grains, cereals, nuts, legumes, seeds, and vegetables

Tryptophan is a precursor to serotonin.

One thing that’s not a myth: tryptophan can have some effect on sleep and mood. Tryptophan is a precursor to serotonin, a neurotransmitter found in both the bowels and the brain, and perhaps best known for its role in managing depression, and sleep cycles. Tryptophan is used in some sleep aids and anti-depressants, to help increase levels of serotonin.

However, simply consuming food that contains tryptophan—which is to say any complete, and some incomplete, proteins—doesn’t directly translate to immediate changes in mood or energy levels. An article published in a 2007 edition of the Journal of Psychiatry and Neuroscience notes that “purified tryptophan” can increase brain levels of serotonin, but “foods containing tryptophan do not.”

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Since every dietary source of protein  has a variety of amino acids, tryptophan has to battle the other eight (or so) for transportation to the brain. The article notes that “tryptophan is the least abundant amino acid in protein [foods],” so it’s not exactly given priority. Even if you ate a LOT of turkey, tryptophan would probably still be waiting its turn in line, and, as such, isn’t causing your drowsiness.

Of note: Generally, researchers assume that the average person consumes adequate tryptophan through a variety of foods that contain protein. If your average protein intake is very low, consult a registered dietitian to see where you can add in additional sources of animal- or plant-based proteins.

Carbohydrates, aka (indirect) tryptophan transporters

That said, there’s one nutrient present on most Thanksgiving plates that could make it easier for tryptophan to hitch a ride. The Journal of Clinical Nutrition published a study showing that eating carbohydrates stimulates the release of insulin and makes it easier for dietary tryptophan to get into the brain. Additionally, tryptophan can be processed in the intestinal tract, where serotonin is also stored and used in digestive processes.

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The truth about tryptophan is that it’s not solely responsible for your post-feast fatigue.

A combination of factors may cause drowsiness after you’re done enjoying a holiday meal (or any meal, for that matter). If you got up early for a Turkey Trot, imbibed in a mid-day drink, or slightly overate at the holiday buffet, chances are you’ll start to feel a little fatigued. In fact, it could be the mashed potatoes, dinner rolls, dressing and pie that are making you groggy. Simple carbs cause blood sugar levels to spike, and when they are eaten in excess–like at Thanksgiving–sugar levels drop just as fast, making you want to go straight from table to couch. The thing about naps, and sleep in general, though is that it helps your body recover from training. So, celebrate your Turkey Trot and time with family and friends by enjoying your meal to the point where you are satisfied, but not as stuffed as the holiday bird. And, if you’re feeling drowsy, a nap may be just what your body needs. 

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