Tryptophan vs. The NFL Fan

A turkey dinner with all the fixins can lead to a

satisfying nap. But the meal usually takes a little

longer than this to have an effect. This fellow might

be more affected by last night’s activities than today’s

meal.

Turkey dinner at Thanksgiving brings the family together, celebrates the bountiful harvest, and puts you to sleep just as the NFL games are ready to start. Many people think that if you eat less turkey and fill up on the other goodies you can escape the post-Thanksgiving meal sleepiness. Other people look forward to eating seconds and thirds and then stretching out on the couch for a long nap, forcing Aunt Ethel to sit in the chair with the spring that surprises you every once in a while.

The culprit, or the hero, in this eat and sleep saga is said to be the tryptophan in the turkey. Other people think that it is simply how much you eat, not the turkey's tryptophan, but it isn’t quite that simple. What is tryptophan, and is it indeed responsible for the snoring that follows Thanksgiving dinner?  Some background will help.

Tryptophan is an amino acid, one of the twenty standard building blocks of proteins. However, tryptophan is the least abundant amino acid in plant and animal proteins; it accounts for only 1-1.5% of the total number of amino acids in proteins. Tryptophan’s large structure and intricate rings make it costly to produce in terms of ATP invested. In fact, it takes so much energy to make that we have stopped making tryptophan all together. Tryptophan is abundant in a number of food sources commonly available to humans, so over evolutionary time we have turned it into an essential amino acid. True, it is essential for life, but here the word “essential” means that we MUST get it from our diet, we cannot produce it ourselves.

The genetic code is how mRNA codons (3 bases sequences)

get translated into a signal to build proteins from specific amino

acids. The first base of the codon is represented by the biggest

letters (ACGU), the middle base is the middle size letters, while

the third position (wobble position) is usually where you see an

amino acid coded for by more than one codon. For instance,

serine is coded for by UCU, UCC, UCA, or UCG. But tryptophan is

only coded for by UGG. Three codons signal the protein to stop

growing, called stop codons (UAG, UAA, and UGA).

Even though it is used sparingly in proteins, tryptophan is crucial - don’t eat enough of it and you die. This is because tryptophan’s most essential functions have nothing to do with protein synthesis or structure – tryptophan is important to your brain function. The crucial neurotransmitter, serotonin, is synthesized only from tryptophan.

It takes two enzymes to turn tryptophan into serotonin (also called 5-HT).  First is tryptophan hydroxylase; hydroxylase means it splits water, here it adds an OH to tryptophan. Next, the amino acid decarboxylase removes a carboxylic acid (COOH), producing serotonin.

The feeling of general well being induced by serotonin also participates in the sleep/wake cycle. So is tryptophan – through serotonin – responsible for the post-Thanksgiving nap? Well… yes and no, it's an accomplice in a larger conspiracy.

Serotonin is used to produce the hormone melatonin, and melatonin promotes sleep, so you could say turkey dinner promotes sleep. But turkey doesn’t have that much tryptophan! Tofu has much more tryptophan than turkey, but you don’t get a post-Chinese takeout urge to sleep, so what gives?

Melatonin is made from serotonin in the pineal

gland. Sunlight stimulates the suprachiasmatic

nucleus (SCN) which inhibits the pineal from

making melatonin. As the sun goes down,

inhibition is reduced, more melatonin is made

and released from the pineal, and sleep is

promoted.

The melatonin effect has to do more with how much of everything else you eat at Thanksgiving dinner, especially carbohydrates. Here is how it works – eating lots of carbohydrates causes a release of insulin into the blood (to reduced blood glucose levels). Another function of insulin is to promote the uptake of some amino acids (but not tryptophan) into muscle cells. This leaves the blood higher in tryptophan as compared to other amino acids than it would normally be.

The brain takes in amino acids through a neutral amino acid transporter, which now finds more tryptophan than other neutral amino acids, so the brain level of tryptophan goes up. More tryptophan in the brain, more serotonin – more serotonin, more melatonin. More melatonin = nap time! So if you want to avoid the post-Thanksgiving nap, eat the turkey and skip the mashed potatoes.

You didn’t know how much tryptophan controlled your daily life, did you? Well, there’s more. Tryptophan is also important in synthesizing niacin, a.k.a. vitamin B3 or nicotinic acid. Niacin is important in production of NAD/NADH for energy metabolism, for production of steroid hormones and balance of lipid forms in the blood, and as an anti-convulsant.

The tryptophan-niacin connection is made stronger by recent evidence that high dietary tryptophan can prevent epileptic seizures in mice. In this study, a whey protein called alpha-lactoalbumin (ALAC) was found to have much tryptophan, much higher levels than in most proteins. Feeding epileptic mice ALAC resulted in reduced numbers of seizures.

So even if you don’t want to sleep or think happy thoughts, you still need to eat food that contain tryptophan or niacin. And many of those foods are plants, because plants use tryptophan to control their own activities. Tryptophan is easily converted to auxins, a type of plant hormone. Auxins are responsible for several different plant behaviors, namely the falling leaves in autumn and ripe fruits all year long.

Here is an interesting attempt to get kids to read

history. During the spring, captive warriors were

killed by cutting out their hearts, then their skin was

flayed off their body, and the priests would wear them

around for 20 days. This was meant to celebrate the

god who sacrificed himself to allow a new growing

season to begin. This time period corresponds

 to when they would have had the lowest amount of

 tryptophan in their daily diet.

Having dietary choices for tryptophan is good, and plants provide our major source. However, cooking grains and corn reduces usable tryptophan and niacin levels dramatically, so poorer environments where corn is the staple food need also to have additional dietary sources of tryptophan. A deficiency of this amino acid leads to some disturbing conditions. Low tryptophan leads to low serotonin levels and agitation, insomnia, and depression. A study in the Archives of General Psychiatry stated that chronically low levels of tryptophan led to relapses of purging behaviors in bulimics.

More amazingly, studies in the 1970’s to 1990’s suggest that low tryptophan levels can lead to increases in religious fanaticism. Several studies from a single author correlate the Aztec human sacrificial ceremonies to the times of year when their diets depended more on foods that had less tryptophan. Think of all the lives that could have been saved by tofu!


Contributed by Mark E. Lasbury, MS, MSEd, PhD
As Many Exceptions As Rules

Russo, E., Scicchitano, F., Citraro, R., Aiello, R., Camastra, C., Mainardi, P., Chimirri, S., Perucca, E., Donato, G., & De Sarro, G. (2012). Protective activity of α-lactoalbumin (ALAC), a whey protein rich in tryptophan, in rodent models of epileptogenesis Neuroscience, 226, 282-288 DOI: 10.1016/j.neuroscience.2012.09.021
 
Bruce KR, Steiger H, Young SN, Kin NM, Israël M, & Lévesque M (2009). Impact of acute tryptophan depletion on mood and eating-related urges in bulimic and nonbulimic women. Journal of psychiatry & neuroscience : JPN, 34 (5), 376-82 PMID: 19721848