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