Saturday, January 16, 2010

The Life and Death of a Fat Cell

As you’ve seen, fat cells are like miniature people—the more fat you feed them, the more they plump up. Unfortunately, even the strictest diet can’t remove them. Instead, it leaves you with billions of slimmed-down fat cells crying out for another meal.

But there’s another side to this story. Different people do have different numbers of fat cells. Not only do obese people have dramatically bigger fat cells than slim people, they often have many more. For years, scientists have wondered what causes these differences. Do fat cells ever die? Does something trigger the creation of new fat cells? Is it our fault?

In 2008, a group of scientists devised a clever experiment to answer these questions. It worked by examining the effect of nuclear-bomb explosions on human fat cells. At first glance, this sounds like a Very Bad Idea. After all, detonating nuclear bombs— even in the name of science—is likely to put off the ethics board. But here’s the trick: the researchers didn’t launch the bombs themselves. Rather, they took advantage of a bit of Cold War history to track radioactive carbon in human fat cells.

Now you’re probably wondering what radioactive carbon is doing in human fat cells, and that’s a reasonable question. The obvious answer is“because the researchers put it there,” but it turns out they aren’t allowed to do that, either. (It’s likely to be toxic.) The experiment was launched, unknowingly, by the American and Soviet militaries when they tested nuclear bombs. These tests sent large amounts of radioactive carbon into the atmosphere that drifted to all corners of the world. Plants pulled it out of the atmosphere, animals ate the plants, and we ate the animals. The end result is that the U.S. and Soviet governments radioactively labeled pretty much everyone who was around at the time.

Here’s a chart that shows how the levels of radioactive carbon soared during nuclear testing and rapidly diminished when nuclear testing went underground in 1963.

By matching the level of radioactive carbon in the air with the amount of it in the DNA of a fat cell (along with a generous pinch of statistical mojo), researchers can figure out when that cell was created. It’s as though each fat cell has its own “manufactured on” date.

To draw their conclusions, the researchers analyzed fat extracted from about 700 people. Here’s what they found:

• The number of fat cells grows through childhood and adolescence, but stabilizes sometime in late adolescence. After that, your fat-cell count stays the same.

• People on the fast track to obesity pack on their fat cells more quickly in childhood and stop producing them around age 16 or 17. Naturally thin people have fewer fat cells, but keep producing them until the age of 18 or 19.

• Even extreme events—for example, dramatic weight loss through surgery or super-sized weight gain—change the size of fat cells in the body, but don’t nudge the number. (That said, many experts believe years of excessive weight gain that lead to hundreds of extra pounds will eventually cause fat cells to multiply.)

• About 10 percent of your fat cells die and are replaced each year, whether you’re thin, fat, or somewhere in between.

No one knows why some people end adolescence with more fat cells than others. There’s a good case to be made that it’s hard-coded in your genes (in other words, blame mom and dad). Events during fetal development and childhood might also play a role—for example, chowing down on calorie-rich food early in life could kick off certain processes in your body, preparing it for a life of fat retention. But no matter the reason, it’s clear that some people enter adulthood set up for caloric challenges, with a big family of fat cells. They won’t necessarily gain weight more easily than a naturally lean person, but they’ll probably feel a stronger pull toward that second batch of chocolate chip cookies.

To put it another way: fat people are doing something wrong. But they’re doing it because their bodies are telling them to.

Source of Information : Oreilly - Your Body Missing Manual (08-2009)

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