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Booster Shots

Overload Those Fat Cells and They Call in Troops

April 29, 2002|ROSIE MESTEL

Scientists used to think that people have a certain number of fat cells and, whatever they do, they're stuck with the blighters for life. But science has marched on, for once with good news. Fat cells do die after all.

Knowing this, of course, doesn't instantly remove five pounds from one's rump. And the fact needs qualifying: Fat cells die--but not very easily, and often they're simply replaced.

Fat cells, as many of us have suspected, are impressively resilient. They're wonders of nature, a fact that I failed to properly appreciate in the past. But now, after talking with fat scientist Susan K. Fried (she studies fat, we mean), I am suitably awed.

Fried, a Rutgers University professor and a member of the North American Assn. for the Study of Obesity, got hooked on the science of fat as a grad student and is still probing the tissue's biology 25 years later. The human body, she informs us, contains 20 billion to 100 billion fat cells. And a gram of fat contains 1 million to 2 million fat cells. Fried knows these things because she's taken samples of fat from all kinds of people, including herself, and examined them under the microscope. She even knows what her own fat cells weigh (0.3 to 0.5 microgram apiece).

Fat cells, Fried explains, balloon when we consume excess calories so that we have a savings account to draw on during lean times. The cells slowly get bigger as we chomp on doughnuts and fries and pasta, accumulating droplets of lipid like there's no tomorrow and inflating to more than double their original volume. If we lose lard, they shrink back down.

For most people, any change in calorie intake is easily accommodated by this concertina-like behavior. But when people gain serious weight (say, 50 to 100 pounds or more) and seriously overeat for at least a month (more, even, than those wild few weeks prior to Christmas), the fat cells fill up and refuse to swell any further. They slam the lipid sluice gates shut. Then they send out for reinforcements.

Help is close at hand--right in the fat tissue, which is really a medley of cells, Fried says. There are turgid, lipid-filled fat cells; little round cells called stem cells; and another class of innocent-looking round ones called "pre- adipocytes."

Innocent they may look, but upon receiving an SOS from the filled-up fat cells, the preadipocytes cease lolling about, transmogrify into fat--and start swelling.

Scientists have detected no upper limit on the number of pre- adipocytes that can be recruited this way. ("It's a--I won't say infinite, but it is a big resource," Fried says.) If researchers can figure out how that recruitment takes place, they might be able to develop drugs to intercept the signal and block the formation of new fat cells in people with serious obesity problems.

Once recruited, fat cells tend to stick around--although they do die and get replaced at a slow, steady rate. Under some circumstances there's even a net loss of fat cells. For instance, the cells seem to die off during the massive weight loss that follows surgery for obesity.

Fat cells are not merely picky about getting too porcine--they also hate to get too small. Pick a fat cell, any fat cell, from a person thin or stout, and it is very unlikely to weigh less than 0.3 to 0.4 microgram, says Fried. Weight loss tends to plateau when fat cells reach that size. Dieters may still look larger than perpetually skinny people--because they've got more numbers of fat cells clinging to their frames. And while they strain to keep dieting, the fat cells fight back--storing lipids with ever more zest, and stimulating their owners' appetite via changes in the hormones they produce.

Scientists have also learned that not all fat is the same. A cell's precise qualities vary according to which "fat depot" in the body it resides in.

Fat from the belly, for instance, is more metabolically active and will lose and gain lipid more quickly than fat from the thigh. Fat from viscera (the inside of the abdomen) is even more active than belly fat. (Scientists would love to know why.)

What's more, "if you transplant fat from one region to another, it remembers who it is," Fried says. An early hint that this was so came in the 1960s when a patient with a burned hand was given a graft from his belly.

When the man gained some weight, the patch of grafted tissue grew a nifty padding of fat that hands do not normally sport.

One wonders if aesthetic plastic surgeons are tapping into this new learning. ("All our lip augmentations guaranteed 100% long-lasting thigh fat!") And should the counterculture ever latch onto fat grafting for 3-D body art, tongue piercings and tattoos are going to look mighty tame.

*

If you have an idea for a Booster Shots topic, write or e-mail Rosie Mestel at the Los Angeles Times, 202 W. 1st St., Los Angeles, CA 90012 or rosie.mestel@latimes.com.

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