Exercise can't overcome the health effects of laziness?

Roni Caryn Rabin of the New York Times writes about "The Hazard of the Couch"

Many of us sit in front of a computer for eight hours a day, and then go home and head for the couch to surf the Web or watch television, exchanging one seat and screen for another. Even if we try to squeeze in an hour at the gym, is it enough to counteract all that motionless sitting?

A mounting body of evidence suggests not.

The latest findings, published this week in The Journal of the American College of Cardiology, indicate that the amount of leisure time spent sitting in front of a screen can have such an overwhelming, seemingly irreparable impact on one’s health that physical activity doesn’t produce much benefit.

Rabin cites two types of studies, one type showing that people who spend more time on the couch watching TV have a higher risk of health problems like heart disease and have a higher chance of dying, and another type that shows that in animal studies some biochemical changes can explain why:

...being sedentary may affect lipid metabolism. Prolonged inactivity appears to sharply reduce the activity of an important enzyme called lipoprotein lipase, which is responsible for breaking down circulating blood lipids and making them available to muscles for energy, Dr. Stamatakis said. Lowered enzyme activity leads to higher levels of fats and triglycerides in the blood, and to a higher risk of cardiovascular disease. Exercise has very little impact on the enzyme’s activity, he said.

So does spending time sitting down, whether it's becoming a coach potato in front of the TV, surfing the internet, or studying books, increase your chance of death?

Well, there's a few problems with her analysis. 

One, just because the two things (spending time on the couch watching TV and health problems) are correlated doesn't mean that spending time on the couch results in a higher chance of death. As one commenter points out: "correlation does not imply causation.Could it be that less healthy people tend to spent more sedentary time than more healthy people?"

Two, laboratory animals are different than humans in ways that make it hard to take results from one species (for example, mice) to another (us, human beings).

Correlation just means that we find that two things tend to go together. For example, people who run more often tend to be faster runners. Being an American citizen has a correlation with being Caucasian. Tables tend to be square instead of round. 

But it doesn't mean that one causes the other. Sure, people who run more often increase their speed and stamina, but oftentimes people who are fast runners take running up as a hobby - because they're good at it. Having a higher chance of being Caucasian if you are an American citizen has to do with a common cause - that most American immigrants throughout come from Europe. And tables and being square have nothing to do with causing each other - tables don't result in being square, and being square doesn't make a table.

So it's completely possible that the people who spend more time on the couch have a higher chance of dying because they're already unhealthy to begin with. A person who is easily tired because of bad health is going to end up on the couch more often than someone who is naturally more energetic, who has a higher metabolism, etc.

It's also possible that other factors, like general laziness, results in both spending more time on the couch and worse heart problems. People who are lazy tend to eat out more often (because they're too lazy to cook. Trust me, I know from personal experience) and laze around on the couch watching nonsense on TV. Of course, fast food mostly is made of hamburgers, pizza, donuts - all the fattiest foods you could ever find. So of course the guys who eat these foods are going to be dying of heart attacks sooner than the guys who don't.

Laboratory animals are also tricky, especially when it comes to diet. When I was in college, I examined polysaturated fatty acids versus monosaturated fatty acids in Siberian hamsters, which hibernates in the winter. Depending on the time of year, they start eating to increase their fat content for the winter, and lose the fat for warmer seasons. Living in the harsh climates of Siberia, their bodies have evolved to work that way.

Of course, human beings don't react the same way.

Another finding shows that only herbivores (plant-eating animals) have trouble with cholesterol when they are fed meat, but carnivores don't. Carnivores have evolved to breakdown all the stuff that becomes plaque and fatty deposits in our bloodstream and body. So clearly, the type of animal that these experiments are conducted on really matters!

What are these animals that had higher levels of fat in the blood when they were "inactive" for long periods of time? Were they animals that hibernated (ie "prolonged inactivity") and therefore needed the fat, or were they more like us? 

We can't know, because Rabin doesn't tell us. And that's exactly why, folks, I often have trouble taking the newspaper's "science" section too seriously.

But not everything's lost. If you went to the actual article, you'll find a cute picture of a fat cat on a couch. I guess everyone has his own blog these days, because apparently he has one too.