Why Does Turkey Make Me Tired? What Makes Dark Meat Dark?

Why does turkey make me tired?

Most people blame tryptophan, but that's not really the main culprit. In case you're wondering, tryptophan is an amino acid that the body uses in the processes of making vitamin B₃ and serotonin, a neurotransmitter that helps regulate sleep. It can't be produced by our bodies, so we need to get it through our diet. From which foods, exactly? Turkey, of course, but also other meats, chocolate, bananas, mangoes, dairy products, eggs, chickpeas, peanuts and a slew of other foods. Some of these, like cheddar cheese, have more tryptophan per gram than turkey. Tryptophan doesn't have much of an impact unless it's taken on an empty stomach and in an amount larger than what we're getting from our drumstick. So why does turkey get the rap as a one-way ticket to a nap?

The urge to snooze is more the fault of the average Thanksgiving meal and all the food and booze that go with it. Here are a few things that play into the nap factor:

Fats "“ That turkey skin is delicious, but fats take a lot of energy to digest, so the body redirects blood to the digestive system. Reduced blood flow in the rest of the body means reduced energy.

Alcohol "“ What Homer Simpson called the cause of—and solution to—all of life's problems is also a central nervous system depressant.

Overeating "“ Same deal as fats. It takes a lot of energy to digest a big feast (the average Thanksgiving meal contains 3,000 calories and 229 grams of fat), so blood is sent to the digestive process system, leaving the brain a little tired.

Why is dark meat dark and white meat white?

Among the many things inside our bodies (guts, black stuff, about fifty Slim Jims), there are two types of muscle fiber: fast twitch and slow twitch. Fast twitch muscle fibers, which contract quickly but consume a lot of energy and fatigue quickly, are used for rapid movements like jumping and sprinting. Slow twitch muscle fibers contract slowly but don't use much energy, and can contract for a long time before fatiguing; they're used for endurance activities.

Most of our muscles are made up of a mix of both slow and fast twitch fibers and, overall, the average human body has about a 50/50 mix of the two. Some people may have a higher percentage of one type or the other from developing those fibers through training and exercise. Some Olympic sprinters have as much as 80% fast twitch fibers and long-distance runners have the same percentage of slow-twitch. Ongoing research says that training can only alter the ratio so much, though. It seems that there's a genetic predisposition for having more of one fiber than another. But let's talk turkey.

The meat we eat from a turkey is turkey muscle, and turkeys have fast and slow twitch muscle fibers, too—though not in the same even mixing we see in humans. The difference between dark meat and white meat is due to the type of muscle fiber that's predominant in the meat and the way that fiber makes energy.

The muscles in turkey legs "“ the dark meat from the thighs and drumsticks "“ are mainly made up of slow twitch fibers, which get their energy from oxygen stored in the fibers by a protein called myoglobin. Myoglobin is a richly pigmented protein, and the more myoglobin there is in the fibers, the darker the meat.

Turkey wings and breasts, the white meat, are mostly made up of fast twitch muscle fibers, which get their energy from glycogen, a polysaccharide of glucose that's stored in the muscle fibers and doesn't have much pigment.

If you've eaten duck breast, you know that it's hardly what you'd call white meat. That's because unlike flightless turkeys, ducks take to the air a lot and have more slow twitch fibers, and more myoglobin, in their wings and breasts.

Thanksgiving by the Numbers

Before we all find a comfortable spot on the couch to curl up in, let's crunch some big numbers that go along with the big meal.

271 million - The estimated number of turkeys raised in the US this year. Of those, 49 million were raised in Minnesota, the leading turkey production state for the year.

$4.3 billion "“ The estimated amount that farmers will make from the sale of all those turkeys.

689 million pounds "“ The estimate for US cranberry production this year. Wisconsin comes out on top with 385 million pounds produced.

1.8 billion pounds "“ The total weight of sweet potatoes produced by the major sweet potato producing states last year.

1.1 billion pounds "“ The total weight of the pumpkins produced last year by major pumpkin-producing states, with a value of $117 million. Illinois wiped the floor with the rest of the states' pumpkin patches and led the country with 542 million pounds worth of gourd.

177 million pounds "“ The tart cherry production for 2008, if pumpkin pie isn't your thing.

13.3 pounds "“ The amount of turkey that the average American ate in 2006.

(If you're a numbers geek, these figures came from the USDA National Agricultural Statistics Service, the USDA Economic Research Service and the Census Bureau, all of which have plenty of other fun stats to play with.)