Does tryptophan in turkey really cause a food coma?
It’s time to talk turkey. Or, more specifically, the tryptophan that we’ve all heard imbues turkey with amazing sedative properties. This episode can provide fodder for Thanksgiving Day dinner table discussions.
Many readers have heard of the Thanksgiving food coma and the idea that the tryptophan in turkey is somehow the culprit. In order to understand whether such a thing exists we must first review tryptophan and establish whether turkey has a lot of it.
Tryptophan is an essential amino acid, meaning that humans must ingest it and cannot make it ourselves. As an amino acid, it should come as little surprise that proteins are examples of foods that are high in tryptophan.
According to the USDA, turkey is pretty rich in tryptophan. But, turkey is nothing special among meats. Depending on the cut and cook, pork, fish, and chicken can all have more. And other foods like cheese have lots of tryptophan too.
Milk is listed as another food high in tryptophan. This may help explain the advice to drink a warm glass before bedtime to relax. Whether that advice is sound, we must soon determine.
The question now becomes, does tryptophan make one sleepy? For this, anecdone won’t be enough. We need data. In one study, participants were given 4 grams of tryptophan, leucine, or placebo. Those receiving tryptophan were more sleepy than those receiving placebo. The difference was seen as early as 45 minutes after ingestion. Not the greatest of data but it is something.
Next comes why? Recall that tryptophan is a precursor of serotonin and melatonin. Both are associated with sleep and sleepiness. So the basic idea is that increased levels of tryptophan will result in increased levels of serotonin and melatonin.
But, there is a problem. In order to lead to sleepiness, tryptophan must get across the blood-brain barrier (BBB) and into the brain. Once in the brain it must undergo conversion to serotonin/melatonin.
And although tryptophan can cross the BBB, it has competition. Tryptophan is one of the large neutral amino acids, along with tyrosine, phenylalanine, leucine, isoleucine, valine, and methionine. These amino acids compete with each other for use of a transporter across the BBB. A series of experiments from the 1970s demonstrated that it isn’t the absolute plasma tryptophan concentration that matters. Instead, it is the ratio of tryptophan to other large neutral amino acids that matters. The higher the ratio, the higher the tryptophan content in the brain.
A natural becomes becomes, do turkey and the other components of the typical Thanksgiving meal lead to a high ratio of tryptophan to other large neutral amino acids? Depending on what your favorite side dishes are, quite possibly. When you eat foods with a high glycemic index (e.g., mashed potatoes) this leads to insulin secretion. The insulin causes skeletal muscles to take up amino acids. But, because tryptophan is albumin-bound, less is taken up, leading to an increase in the Trp/LNAA ratio.
So, if you like mashed potatoes and bread with your turkey that places you at risk for a high tryptophan to large neutral amino acid ratio. And if this ratio is high, more tryptophan can cross the BBB, get converted to serotonin and melatonin, and make you drowsy.
That’s the theory, yes.
There are a few problems with this explanation. The biggest might be the dose of tryptophan. In the first study mentioned above, the one where they gave people tryptophan, leucine, or placebo, the dose of tryptophan was 4 grams. There are about 400 mg of tryptophan in a pound of turkey. So, one would need to eat 10 pounds of meat to get to 4 grams. That would be a turkey of over 20 pounds.
The other problem goes back to the concept that the main determinant of brain tryptophan concentrations is not the plasma tryptophan level, but the trp/LNAA ratio. So you might compare two Thanksgiving plates. One is all turkey. Lots of tryptophan and no carbohydrates. The other is all mashed potatoes. No tryptophan and tons of carbs. The plate of turkey is more likely to lead to a rise in plasma tryptophan levels. But, mashed potatoes are more likely to induce sleepiness. That’s because the turkey also has the other LNAA and the ratio won’t change. As a result, the brain levels won’t increase. But the mashed potatoes WILL lead to an increased ratio and will lead the movement of tryptophan into the brain.
So, is turkey-induced food coma all a myth?
It’s quite likely that the turkey, tryptophan, food coma connection is a myth. In some ways, a plate of just turkey may be your best protection against the Thanksgiving food coma. But the idea that Thanksgiving, with all the carb-heavy food, alongside alcohol, travel, and exhausting conversation might lead to a coma. That comes as no suprirse.
Take Home Points
- Yes, turkey has tryptophan
- No, we probably don’t eat enough turkey during our Thanksgiving meals to lead to significantly high levels so as to cause severe drowsiness
- Mash potatoes are probably more sleep-inducing
- Thanksgiving is tiring
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Credits & Citation
◾️Episode and show notes written by Tony Breu
◾️Audio edited by Clair Morgan of nodderly.com
Breu AC, Cooper AZ, Abrams HR. Thanksgiving & The Food Coma The Curious Clinicians Podcast. November 24, 2021