Who Will Live Longest?

Here's a medical pop quiz: Frick and Frack are friends who sport matching spare tires around their waists. Frick goes to Weight Watchers and loses 30 lbs.; Frack goes to the ice-cream parlor and downs a triple banana split every day for a month. So who will live longer? Anybody with a clue about obesity knows that conscientious Frick has lowered his risk of heart disease, high blood pressure, diabetes and stroke. Frack has done exactly the opposite.

But anyone who read last week's issue of the journal Tissue Engineering knows that Frack could someday have a big advantage if a new piece of research can be turned into a practical treatment. According to scientists at UCLA and the University of Pittsburgh, the unsightly flab many of us lug around is a previously unsuspected source of stem cells, a remarkably versatile class of cells that can in principle be transformed into a variety of body tissues. Researchers already suspect that stem cells found in fetuses and in the bone marrow and brains of adults might one day be used to repair hearts, livers and other organs.

Each of these sources, however, is problematic. Bone marrow and the brain are difficult or painful to get to surgically. And cells from in-vitro embryos and aborted fetuses pose ethical and political problems. Indeed, President Bush is soon likely to make right-to-lifers happy by reimposing a ban on using federal funds for research on such tissues. (Another possible source of stem cells announced last week--the placentas of pregnant women--avoids these problems but hasn't been confirmed.)

Fat cells, by contrast, are plentiful and easy to harvest--just ask anyone who has had liposuction. They are also rich in stem cells--not so surprising, in retrospect, since bone marrow and fat develop from the same embryonic tissue. Not only did the researchers get stem cells from liposuctioned human fat, they also made them grow into bone, muscle and cartilage cells--a sign that more ambitious tissue engineering is not out of the question.

Unfortunately, these particular stem cells are already partly specialized, so they might not help Frack's hardened arteries or the insulin-producing cells in his pancreas (though other types of stem cells might). But in principle, he could mine his love handles for cells to repair his damaged liver, to replenish blood cells lost to disease, to fix a damaged heart or to repair missing or deteriorating cartilage. And because the cells would be drawn from his own body, Frack wouldn't have to worry about having his immune system reject them.

None of this means that Frack should be considered a role model, though. Stem-cell tissue replacement is half a decade off at least, and nobody knows what unexpected glitches might arise to make the whole idea impossible. Besides, the hazards of true obesity are enormous. But if the research pans out, it may someday be as prudent to carry a modest spare tire around your waist as it is to carry one in the trunk of your car.