The scene: A crowded dining room, serving dishes and utensils scattered around the table. Family members lean back in their chairs contentedly, relaxed conversation drifts through the air. It’s Thanksgiving evening, and you’ve just finished tucking into broiled turkey, loaded stuffing, mashed potatoes, rolls and pumpkin pie. Most of us know what’s coming next — the undeniable urge to take a long nap.

Thanksgiving turkey, and the tryptophan it contains, has long been held responsible for an epidemic of sleepiness that hits like clockwork every third week in November. There’s a simple, though misguided, reason for this: Among its many other functions, the essential amino acid is synthesized by our bodies into melatonin, a hormone that helps tell our bodies when it’s time to go to sleep.

But an excess of tryptophan may be the least of the culprits behind our post-feast drowsiness. Indeed, simply eating such a large meal, especially one traditionally heavy in carbohydrates, is enough to send us to bed. And to further puncture the myth, turkey isn’t even an abnormally rich source of tryptophan. It ranks just ahead of foods like chicken and behind egg whites and soybeans.

As this Thanksgiving approaches, we’re here to give you the real scoop on tryptophan and explain some of the science behind your well-earned holiday nap.

Does the Tryptophan in Turkey Make Us Sleepy?

Tryptophan molecular structure
Human beings cannot make the vital amino acid tryptophan in their bodies, it must come from the diet. Fortunately, there are many excellent food sources.

Tryptophan is one of nine essential amino acids that our bodies need to function. They’re called essential because our bodies cannot make them on their own, which means we must get them from our diets. Amino acids are used to make proteins, a fundamental building block of the human body, and other key biological molecules. Meat and seafood are major sources of amino acids, as well as dairy and some plants like soybeans.

After a hearty Thanksgiving dinner, the tryptophan we ingest is turned into the hormones serotonin and melatonin, as well as niacin, or vitamin B3 (MedlinePlus). Serotonin is a neurotransmitter that helps neurons “talk” to each other, and is linked to feelings of well-being and happiness. It also has other roles throughout the body, including in the digestive and cardiovascular systems (Berger et al., 2009).

Melatonin is a hormone associated with our bodies’ circadian clocks, responsible for sleep-wake cycles, appetite regulation and more. It’s released by the pineal gland, located deep within the brain. Increases in melatonin levels help prepare the body for sleep, and the hormone is often sold over the counter as a sleep aid. There’s also evidence that melatonin has antioxidant properties (Reiter et al., 2010). Melatonin levels in the body can indeed increase after a meal with a lot of tryptophan in it. But that’s not the main reason you nod off after your second helping of turkey and mashed potatoes.

Why We Fall Asleep After Thanksgiving Dinner

The first, and most crucial piece of evidence exonerating turkey as a narcoleptic drug is a simple one. Many common foods contain more tryptophan than turkey does, according to the U.S. Department of Agriculture. One hundred grams of turkey has about .24 grams of tryptophan. Compare that to .32 grams for the same weight of cheddar cheese, and a whopping .59 for raw soybeans. In fact, chicken and beef both have about the same amount of tryptophan as turkey. And even oats, baking chocolate and quinoa deliver significant doses of tryptophan.

So, turkey isn’t particularly sleep-inducing. But tryptophan does lead to melatonin, which we know makes us sleepy. So, there’s some reason to think that eating a lot of turkey (or chicken or cheese) might make us sleepy. Be that as it may, melatonin likely isn’t the chief reason you fall asleep after a Thanksgiving meal. For that, we can thank the rest of the dishes you’re loading onto your plate, and especially those heavy in carbohydrates.

Most Thanksgiving meals contain large portions of carbohydrates — thanks to the rolls, mashed potatoes, stuffing, pies and other bread- and starch-based dishes. Carbohydrates, especially the simple sugars found in many modern foods, are processed quickly by our bodies and turned into glucose in our blood.

This glucose, or blood sugar, is easy energy for the body, and it’s quickly used up. That creates a quick spike followed by a crash, also known as postprandial hypoglycemia (Yüksel Altuntaş, 2019). Put simply, too many carbs means you’ll be feeling tired in an hour or two.

(Read more: Why It’s Harder to Fast If You’re Eating Too Many Carbs)

Dinner rolls on table with Thanksgiving food
There…just beyond the turkey…we’ve found the culprits!

The final sleep-inducer involves insulin, the brain and, actually, tryptophan. When we eat a lot of carbohydrates, our bodies respond by releasing insulin into the bloodstream. Insulin is necessary for cells to import glucose through their cell membranes. But, thanks to a complex metabolic process, all that insulin also has the side effect of increasing the amount of tryptophan reaching our brains, where it is converted into melatonin (Daniel et al., 1981).

That mechanism is backed up by studies of carbohydrate intake and metabolism. For example, a 2003 study showed that meals high in carbohydrates elevate both insulin and tryptophan levels more than meals high in protein (Wurtman et al., 2003). And another study from 2007 found that carb-heavy meals resulted in participants falling asleep much quicker after they went to bed than those who had a low-carb meal (Afaghi et al., 2007).

Bottom Line

While you may be nodding off after Thanksgiving this year, don’t blame the turkey. The pleasant somnolence we experience after a heavy holiday meal is due to a number of factors, especially the carbohydrate-heavy nature of the feast. If you want to avoid feeling sleepy after your celebration (though it’s also fine if you don’t), try going light on the rolls and stuffing and add some more vegetables and lean protein to your plate.

And we’d be remiss if we failed to mention one way to liven your Thanksgiving meal up this year: bring some seafood to the table. Check out some of our tasty, festive recipes, like a smoked salmon pot pie with chive biscuits, sardines simmered with roma tomatoes or Chilean sea bass with spice rub, corn risotto and avocado salad.

In short, fewer carbs and more seafood might yield your liveliest holiday yet – enjoy!

 

Citations:

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Altuntaş Y. Postprandial Reactive Hypoglycemia. Sisli Etfal Hastan Tip Bul. 2019;53(3):215-220.  doi:10.14744/SEMB.2019.59455

Berger M, Gray JA, Roth BL. The expanded biology of serotonin. Annu Rev Med. 2009;60:355-66. doi: 10.1146/annurev.med.60.042307.110802. PMID: 19630576; PMCID: PMC5864293.

Daniel PM, Love ER, Moorhouse SR, Pratt OE. The effect of insulin upon the influx of tryptophan into the brain of the rabbit. J Physiol. 1981 Mar;312:551-62. doi: 10.1113/jphysiol.1981.sp013643. PMID: 7021801; PMCID: PMC1275568.

Hasselgren PO, Warner BW, James JH, Takehara H, Fischer JE. Effect of insulin on amino acid uptake and protein turnover in skeletal muscle from septic rats. Evidence for insulin resistance of protein breakdown. Arch Surg. 1987 Feb;122(2):228-33. doi: 10.1001/archsurg.1987.01400140110015. PMID: 3545143.

Reiter RJ, Tan DX, Fuentes-Broto L. Melatonin: a multitasking molecule. Prog Brain Res. 2010;181:127-51. doi: 10.1016/S0079-6123(08)81008-4. PMID: 20478436.

Tryptophan. MedlinePlus. Reviewed 1/7/2020. https://medlineplus.gov/ency/article/002332.htm

 Wurtman RJ, Wurtman JJ, Regan MM, McDermott JM, Tsay RH, Breu JJ. Effects of normal meals rich in carbohydrates or proteins on plasma tryptophan and tyrosine ratios. Am J Clin Nutr. 2003 Jan;77(1):128-32. doi: 10.1093/ajcn/77.1.128. PMID: 12499331.