Tryptofacts and Tryptofantasies

Have a Sleepy Thanksgiving!

Is the post-meal drowsiness felt by many on Thanksgiving caused by turkey?

After eating a Thanksgiving meal, have you felt like the button on your pants is going to burst and you need to lie down and take a nap? If you’ve had a few holiday dinners where you’ve felt tired after, you may have made a connection between eating turkey and sleep. You might have even learned that a chemical in turkey called tryptophan causes drowsiness.

Tryptophan

Tryptophan is an essential amino acid, and it must be obtained from the diet. It is among the less common amino acids, but it plays important structural and functional roles. Tryptophan helps to “anchor” proteins within the cell membrane. Like all amino acids, it is one of the building blocks of proteins, but it also has non-protein functions. For example, tryptophan is used by the body to produce the neurotransmitter serotonin (which controls mood), the hormone melatonin (which controls sleep), and the nutrient niacin (vitamin B3) (which helps convert food to energy).

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Tryptophan & Serotonin

Because tryptophan is ultimately converted into the neurotransmitter serotonin, it has been proposed that consumption of tryptophan may improve depression symptoms. Tryptophan is currently sold over the counter in the US (after being banned 1989–2005) as a dietary supplement for use as an antidepressant and sleep aid. Federal law does not require dietary supplements to be proven safe to the FDA’s satisfaction before they are marketed. Further, manufacturer’s claims about their product do not need to be proven accurate to the FDA before they are marketed. Potential side effects of tryptophan supplementation include nausea, diarrhea, lightheadedness, headache, dry mouth, blurred vision, sedation, euphoria, and involuntary eye movements.

Tryptophan & Turkey

Tryptophan is present in most protein-based foods. It is particularly plentiful in chocolate, oats, milk, yogurt, red meat, eggs, and fish. Contrary to popular belief, the tryptophan content in turkey is typical of all poultry. Comparatively, 3 ounces of canned tuna contains 240 milligrams of tryptophan while 3 ounces of turkey only contains about 160 milligrams. The recommended dietary allowance of tryptophan for most adults is 250–425 mg per day.

Tryptophan in the Body

When you consume protein, your body breaks it down into its constituent amino acids. These amino acids dissipate into the bloodstream, but when they reach the blood-brain barrier they hit a bottleneck — the amino acids compete to get through the barrier. Under normal conditions, this competition makes it unlikely that enough extra tryptophan will enter the brain to significantly boost serotonin levels. But there is an exception.

The Holiday Meal: Gluttony

Thanksgiving Feast

If you consume a lot of carbohydrates (potatoes, stuffing, pie), your body boosts its insulin production. Among its other functions, insulin selectively removes certain amino acids from the bloodstream. But it doesn’t remove tryptophan. Therefore, tryptophan has less competition from other amino acids so more of it can get through the blood-brain barrier. Once tryptophan is converted into serotonin, the pineal gland in the brain further metabolizes the serotonin into melatonin, making you sleepy.

Many people gorge themselves at the Thanksgiving table. During the resultant digestive process, the body diverts as much as fifty percent of its blood to the small intestine to maximize absorption of calories and nutrients. That means there is less blood available for physical activity. Furthermore, most traditional Thanksgiving meals are high in fat and protein, which slows digestion even further.

3 ounces of chicken has 200–300 mg of tryptophan; 3 oz of tilapia has 230 mg of tryptophan

“Feast-induced drowsiness” is the result of a heavy meal rich in carbohydrates, which indirectly increases the production of melatonin in the brain, and thereby promotes sleep. Any big meal containing tryptophan and lots of carbohydrates can trigger sleepiness — not just turkey.