In the US, we are once again preparing for that glorious day of turkey, Thanksgiving. The stuffing is being prepared, the cranberry sauce just as Grandma would have wanted it, the pies are getting baked…and the search engines are alight with thousands (if not millions) of Tryptophan queries as curious dinner guests wonder if eating the traditional turkey will excuse their post-dinner slumber. The answer is still no.

However, tryptophan is one of the essential amino acids that we need to consume to maintain a healthy life. In fact, the lack of tryptophan in a diet was seen in a dire way in the 19th and early 20th century epidemics of pellagra. Pellagra is a devastating illness caused by a chronic deficiency of niacin, which is a natural product of tryptophan. Symptoms such as dementia, skin lesions, ataxia, diarrhea, and ultimately death were only restrained through the work of doctors like Joseph Goldberger and Tom Spies (among others) who pieced together the puzzle of this very avoidable disease. Contrary to some popular belief, turkey (or even meat) is not the sole source of tryptophan. This amino acid can be found in a wide variety of foods including, eggs, soybean, fish, meat, milk/cheese, oats, wheat, potatoes and various vegetables and fruit. So in the event that you might a vegetarian, you don't have to worry about having to take additional supplements in order to include tryptophan into your diet.

But what if there’s even more to the story? Adrian Williams and Robin Dunbar seem to think so. In the International Journal of Tryptophan Research (Really! Tryptophan has its own journal!), they outline a fascinating hypothesis concerning the historical implications of increased ingestion of meat, and therefore tryptophan, creating a surplus of niacin and nicotinamide which may have helped to fuel our pre-historic, evolving brains. Oh…and tuberculosis may have been a beneficial symbiont way back then. Williams and Dunbar believe that TB acted in a symbiotic relationship with humans for thousands of years, producing nicotinamide as a byproduct and bolstering the human vitamin demand during occasional meat famines. This advantage meant that humans, in a hunter/gatherer society, would not immediately suffer the pains of vitamin deficiency such as pellagra during such lulls in food availability. The side effect was that if meat could not eventually be found, TB would cause eventual death. But if the famine subsided, the side effects of TB could again be reduced to its quiet, symbiotic relationship.

That’s a remarkable hypothesis for the tryptophan metabolic pathway and I’ll be very interested to see if Williams and Dunbar can back up their pilot claims with some kind of experimental proof. Until then, might I suggest that you partake in some extra turkey this Thanksgiving holiday with the full knowledge that you are contributing to the brain-enriching habit of niacin production and human brain evolution. Really! Go ahead! Your genetically superior, genius-level descendants will thank you…probably on their future version of Thanksgiving.

Happy Thanksgiving!!

Williams, A. C., & Dunbar, R. I. (2013). Big Brains, Meat, Tuberculosis, and the nicotinamide switches: co-evolutionary Relationships with Modern Repercussions?. International journal of tryptophan research: IJTR, 6, 73.

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