'Tis The Season To Be Unconsciouss
During last week's show, we had a caller on the air asking a question that occurs frequently around this time of year - why is it that you always pass out on Grandma's couch twenty minutes after eating that big Thanksgiving or Christmas dinner? Unless Granny is lacing the stuffing with NyQuil, the culprit most likely to be named is tryptophan, and this is the answer we gave on air. However, in the interest of scientific and journalistic integrity and accuracy, some followup must be put to this claim. After doing further research into holiday-related postprandial sleepiness, we've discovered that turkey is falling victim to a smear campaign of urban legend. This Week In Science regrets that we were hasty to assign guilt to the bird and its much-maligned tryptophan and will attempt to shed some further light on the matter.
Turkey's secret sleep molecule is properly named L-tryptophan. We can see that much of its bad reputation stems from a couple undisputable facts. For instance, L-tryptophan is a precursor of
serotonin, and is an essential amino acid that naturally occurs in turkey protein. Serotonin is known to have a sedative effect, and infact until 1990 consumers in the U.S. could purchase L-tryptophan as a natural sleeping-aid supplement until the FDA removed it due to some contaminated batches (nothing was wrong with the tryptophan itself). So we do know that tryptophan itself can have a calming effect or induce a state of drowsiness. But is it solely the turkey's fault?
L-tryptophan occurs naturally in turkey protein, true. But it also turns up in chicken, beef, and even many plants that are a normal part of the American diet. Ground beef will usually contain a similar amount, pound for pound, of tryptophan that turkey will have. And it is quite interesting to note that light meat chicken will on average contain
more tryptophan than light meat turkey! But we don't very often hear of people passing out from chicken nuggets or hamburgers. Hmmm... something else is afoot.
We had the technicians in This Week In Science's Gastrological Lab run a few experiments, and the've turned up some results of note. It turns out that a solid diet results in faster onset of sleepiness than does a more liquid intake. This was found to be true whether it was low-fat/high-carb or vice versa, but that highest onset of sleep would occur with a mostly solid-food based, high-protein/high-fat/high-carb meal. A holiday meal usually has these attributes, combined with the fact that on average a person will consume a larger gross mass of food at such meal settings than they otherwise would for a normal lunch or dinner in which they would eat foods containing L-tryptophan. Put simply, lots of food makes you tired regardless. Furthermore, the activity of digesting large meals has an effect on gastrointestinal bloodflow which may also help explain feelings of drowsiness. Bloodflow in the intestines can reach up to 50% higher than normal after eating a huge holiday dinner, thanks to the release of increased amounts of adenosine, one of a suite of powerful vasodilators that are present during heavy digestion. All this blood in your belly takes some away from your brain, which can make you sleepy.
So, try not to be too hard on the bird. The tryptophan is part of the reason why you get tired, but it's really not wholely responsible. Don't eat until you get stuffed, and you probably won't get sleepy. Of course, it can be considered rude not to try at least some of everything so you may as well not worry about. Besides, the after-dinner nap is often the best part of the holiday season. And it sure beats eating that hippie Tofurkey...
current science news posted by ted at 12/15/2001 01:48:00 PM
Scientists
& Engineers for America
RSS
