Saturday, November 22, 2008

Phun Physiology: Don't Blame the Turkey for that Thanksgiving Post-Dinner Nap

Ever planned to do a little cycling Thanksgiving day, but just couldn’t get going after one of those family sanctioned annual food eating contests?

You feel like lying around on the couch. The fireplace glow puts your eyelids at ease. Lions and Cowboys run around on TV. Lost in reverie, you count drumsticks on John Madden’s Thanksgiving bird.

An involuntary twitch and you awaken. Did you say, “Bicycle ride?”

Forget it. You might as well enjoy another round of turkey alongside cranberries hemmed in with a wedge of dressing topped off with a slice of sweet potato pie before lapsing once more into a food coma.

We’ve all heard that turkey makes you sleepy. Some claim it’s an enzyme. Others say it’s tryptophan. Either way, I’m sorry to inform you that it’s nothing more than just another urban legend.

It’s true that L-tryptophan, an essential amino acid, is found in turkey. It’s also true that tryptophan is a precursor both to serotonin, a brain chemical that helps us relax, and to melatonin, a brain chemical that makes us sleepy. Moreover, it’s true that tryptophan can be purchased over the counter as a sleep aid.

But personally, between you and me, the only straightforward indication I’ve ever found connecting tryptophan with sleep are the glassy looks people get when they’re presented the chemical pathway of tryptophan.

Take it from my friend, specialist and spokesbird, Tommy Tee, here, who explains the real cause of sleep following that Thanksgiving dinner: overindulgence.

“In the first place,” Tommy Tee explains, “tryptophan is no more concentrated in turkey than it is in chicken, ham, hamburger, or cheese for that matter. And none of them are blamed for sleep.”

Tommy Tee adds, “You got no right to pick on us turkeys!”

I’ll pick it up from here. Tommy Tee gets way too agitated on this subject.

Second, as a sleep aid, tryptophan must be taken in pure form on an empty stomach. This ensures that it is the only amino acid available to the brain. This is not the case when we eat meat which normally contains 20 different amino acids all vying for brain access. Tryptophan’s somnambulant effect decreases when we eat a slice of turkey compared to popping a tryptophan pill.

On the other hand (or, drumstick, if you prefer), let’s take a closer look at Tommy Tee’s overindulgence hypothesis as the cause of after dinner sluggishness. Thanksgiving dinner consists not only of turkey but an endless provision of carbohydrates and lipids.

Carbohydrates play a huge role in promoting sleep. In fact, without carbohydrates, tryptophan cannot make us sleepy. Carbohydrates—the starches and sugars from dressing, sweet potato pie, cranberries, rolls, and so on—cause a gush of insulin. Insulin in turn induces muscles to absorb amino acids from the blood with the notable exception of tryptophan. The result is a relative increase in blood tryptophan, which can now exert greater influence on the brain. In fact, the more carbohydrates we consume, the greater tryptophan’s influence on the brain.

What about fat? What would Thanksgiving dinner be without dressing or collard green drippings? Fats take even longer to digest than carbohydrates or proteins. In the process, they divert even more blood for digestion and away from the brain dulling our senses.

What about seconds? The more helpings we consume, the more blood we need for digestion, again, leaving less for the brain.

Did I mention sipping on an adult beverage, which acts as a nervous system depressant?

So, while it is true that tryptophan promotes sleep, a dinner consisting solely of turkey cannot make us sleepy. We could just as easily invite sleep by eating ham, hamburger, or chicken as long as we pile our plates high with plenty of carbohydrates and fats. Any holiday dinner will do!

What is my advice for cyclists this Thanksgiving?

Personally, I wouldn’t think of missing Thanksgiving dinner. Nor am I going to hold back on the goodies. My buddy, Tommy Tee, and I are going to stick to our game plan. “Gobble, gobble!” he says.

Think of it this way: Thanksgiving dinner is a wonderful opportunity to carb load in anticipation of December’s R-12. After all, most of us should be awake by then!

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