I always remember a Seinfeld episode where Jerry and George become addicted to playing with an antique toy collection belonging to Jerry's girlfriend, and use wine and turkey to drug her into naps. What's that thing in turkey that makes you sleepy, George and Jerry? Tryptophan!
So it hazards a chance that sometime after your family Thanksgiving meal, when the kids have long left the table and the Detroit Lions are embarrassing themselves in their lone annual national appearance, someone will look around at the clan, delirious from a giant meal and trot out an old trope as to why all the logy faces - that mischievous, impish molecule - tryptophan - has put us all to sleep, said to be found in titanic proportions in that marquis entree, the turkey.
Tryptophan myths and what really brings you down on Happy T - the technical term being post-prandial somnolence - have been running around the Thanksgiving table like chummy cousins for at least the last twenty five years. But indeed, there's little credence to the idea tryptophan is an ultimate torpor torpedo.
Tryptophan is one of those 20 essential molecules called amino acids that humans need to find in their diet as the body lacks sufficient metabolic machinery to effectively create them from other materials. Amino acids are the building blocks of peptides or more commonly, proteins of all styles which make up you and me and buffaloes, Venus flytraps and the H1N1 influenza virus. The amino acids are all like various types of construction material with their own individual character. Some make loops and some make bends, others are straight and others have side chains like branches of a tree, sticking out in various means to provide all sorts of flavor to your protein creation. Tryptophan also offers some other uses to living things, being a precursor of plant-growing hormones called auxins or the essential nutrient niacin, Vitamin B3. A variant of tryptophan is even used by the curious cone snail as a component of its venom, contryphan, a neurotoxin it can jab into prey with its harpoon-like tongue called a radula.
The seed of this myth likely comes from a series of experiments at Oxford University where people were asked to drink a special amino acid mixture and then have them participate in the Prisoner's Dilemma, a game based on mutual cooperation. As players were deprived of tryptophan in their drink, indeed, those players will significantly less likely to cooperate. So there does appear to be a biochemical underpinning to the myth. Tryptophan is the substrate, or starting material for the synthesis of serotonin and in turn, melatonin, neurotransmitters both of which have a hand in regulating our circadian rhythm and need for sleep. From here it's just an irrational but tempting leap to conclude that big delicious bird is going to put you down for a few hours as it jams your head full of sleepy chemicals.
But that's not the end of the story.
While you can find tryptophan in turkey, there's no more per gram of protein than you'd find in chicken or cod or even beef. Indeed, there are a multitude of foods where tryptophan racks up in abundance including milk, eggs, soybeans and sesame seeds. You'd soak your system in tryptophan at about double the rate if you drank milk at equal levels you ate turkey. To go even further, tryptophan is the least abundant amino acid commonly found in natural protein, so as you load all that turkey into our guts, tryptophan has to get into the brain by the same blood-brain barrier gateways as all the other, far more abundant proteins. The stunning fact is your tryptophan levels in your brain (and thus, able to sing its psychotropic lullaby) will actually decrease with a meat-rich Thanksgiving meal of any stripe.
So chances are good that not only are the tryptophan levels in turkey insufficient to trigger a sleepy state in their best cases, they likely never get anywhere near a location of effect due to the giant protein meal actually depleting tryptophan levels as the large quantity aminos bull their way into the brain.
A better culprit of that bloaty corpse feeling? Those dreaded carbs.
It's a well-established fact in multiple animal models and human experiments that ingesting large volumes of carbohydrates provokes the release of insulin into the bloodstream. Insulin promotes the absorption of of branched amino acids, specifically large neutral branched chain amino acids into the muscle, but not tryptophan. This leaves tryptophan in the blood without competition as we saw earlier to get through that blood-brain barrier gateway. Once in the brain, then the raphe nuclei - the serotonin factories of the brain suddenly get a big shipment of tryptophan, convert it into serotonin and then to melatonin, the master sleep neurohormone,in the pineal gland, and turn the lights out. While tryptophan is a player in this model, it is those helpings of potatoes, stuffing, cranberry sauce and pie that put you down on the couch until those Turducken drumsticks are handed out to whomever whipped the Lions that day.
Tryptophan was actually marketed in the late 1980's as a diet supplement, boasted as a cure-all for depression, seasonal affective disorder, hypertension, obesity and even obsessive-compulsive disorder. A contaminated batch of L-tryptophan that led to the disability of hundreds and the deaths of 37 people, triggering a ban from the FDA in 1991. After the dust had settled and the contamination well-characterized, the FDA scaled back the ban in 2001 but still expressed skepticism:
"Based on the scientific evidence that is available at the present time, we cannot determine with certainty that the occurrence of EMS in susceptible persons consuming L-tryptophan supplements derives from the content of L-tryptophan, an impurity contained in the L-tryptophan, or a combination of the two in association with other, as yet unknown, external factors" Link
So enjoy that Happy T this year, take time to listen to grandma, take the Lions lightly, and have fun. But whatever you do, when you begin to feel catatonic, don't blame the tryptophan.
Maybe Jerry's girlfriend is just a lightweight drinker, afterall.