Many believe that turkey is to blame for the several-day recovery we all endure at least once per year. Perhaps the most famous (and only) Thanksgiving myth says that consuming large quantities of tryptophan, an essential amino acid contained in turkey, causes our bodies to become fatigued and our minds complacent. However, studies show that consuming more Turkey—as well as most other meats, which contain comparable amounts of tryptophan—may actually make your mother-in-law a little more tolerable. But don’t eat too much food, for it could reverse the chemical’s potentially positive effects.

The brain functions properly when levels of the neurotransmitter serotonin are appropriately high in the brain. The chemical works to facilitate communication between neurons. Low levels of serotonin have been linked to depression, generalized anxiety disorder, and social phobias. Treatment for these disorders often include a prescription for a selective serotonin reuptake inhibitor (SSRI), which slows reabsorption of serotonin by the neurons, leading to higher concentrations of the neurotransmitter outside of the neurons. Tryptophan is the chemical precursor to serotonin. The brain needs sufficient levels of tryptophan in order to make serotonin.

Disorders like fructose malabsorption and lactose intolerance prevent tryptophan from being properly absorbed in the intestine, reducing blood tryptophan concentration. A reduction in blood tryptophan concentration is thought to cause a reduction in the brain’s serotonin levels. People who suffer from these conditions may be told to take tryptophan supplements or even be given a prescription for Tryptan (L-tryptophan), which is thought to increase tryptophan available for conversion into serotonin. However, scientist have not yet proven that we can stave off depression by consuming more tryptophan. Research has shown that blood tryptophan levels generally aren’t altered by a change in diet, suggesting the possibility that low blood tryptophan levels may actually be a symptom of depression rather than its cause. Some studies have reported successful treatment of depression with tryptophan, but many doctors believe these studies suffer from significant methodological flaws that make them inconclusive.

Chronic fatigue can be a sign of depression. Those who are treated successfully often experience their energy levels return to normal. So if tryptophan does in fact function as an antidepressant (or an augmenter of antidepressants), we wouldn’t expect it to make one tired. Some pharmaceutical research has supported this assumption: studies have shown that tryptophan makes for an unreliable sleep aid. Thanksgiving fatigue is actually the result of acute massive carbohydrate consumption. Carbohydrates are broken down into sugar and absorbed into the blood stream, causing a massive spike in blood sugar levels. This spike triggers the release of insulin, a hormone that regulates the absorption of sugar from the blood by cells within the body. Insulin causes cells to absorb neutral branched-chain amino acids (BCAA) but not tryptophan into the muscles. This increases the ratio of tryptophan to BCAA within the blood stream and the excess tryptophan passes through the blood-brain barrier into the cerebrospinal fluid. The tryptophan is converted into serotonin, which is further converted into melatonin.

Melatonin is a chemical responsible for drowsiness. While tryptophan eventually might be turned into melatonin, the tryptophan coming from your Thanksgiving turkey is as much a victim of carbohydrates as that mother-in-law’s waistline. We should really point the finger at the stuffing, cranberry sauce and sweet potato casserole (which, by the way, I find absolutely disgusting—perhaps I just need a better recipe). There’s some anecdotal evidence for the benevolence of tryptophan. In the most recent episode of Mythbusters, team members investigated whether turkey is responsible for drowsiness. The “participants” completed a reaction-time test after consuming holiday meals varying in the inclusion of turkey and the portion size. It turned out that the amount of food eaten had a much greater affect on reaction-time performance than the inclusion of turkey. The myth was declared “Busted.”

Gobble Gobble.

About the Authors

Kristian Marlow, M.S.

Kristian Marlow is a graduate student at the University of Missouri-St. Louis and a member of the St. Louis Synesthesia Lab.

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