You might find this hard to believe, but fat cells require constant attention to maintain their girth. Many people who have tried to improve their looks by having fat injected into their lips and cheeks have seen their enhancement melt away when the transplanted fat cells refused to flourish in their new locations. When researchers investigated this phenomenon, they found that not only had the once- plump cells slimmed down to fusiform slivers, some had changed into an entirely different type of cell, called a fibro-cyte, the type of cell most prevalent in the tissues into which the fat cells had been injected.275 Apparently, fibrocytes surrounding the transplanted fat cells refused to make the introduced cells feel at home (by producing the necessary fat-sustaining hormones). Without these hormones, the receptors and enzymes that enable fat cells to do their thing—ingest sugar and fat and grow pudgy—began to shut down. Shrinking under the peer pressure of a hormonally cold shoulder, the unwelcome guests simply conformed to the rules of the neighborhood and reinvented themselves as fibrocytes.
You may be able to coerce fat cells into becoming just about anything you want. Fat tissue belongs to a class of body material called connective tissue, which collectively includes collagen,
bone, muscle, blood, and associated cells. Some cell biologists now believe that one type of connective tissue cell permanently retains its ability to transform into another cell type whenever chemical signals instruct it to do so. So muscle cells can become fat cells; fat can become bone; and then a bone cell can change back to a fat cell again. This process is termed transdifferentiation. (See Figure 2). As I’ll discuss later, there is evidence that the potential for transdifferentiation may even extend across all tissue types.276,277,278,279
All this suggests that a fat cell on your thigh today might once have been a muscle, bone, or skin cell, living someplace else in your body. But why, you may wonder, would any cell decide to pack its bags and head to an entirely new location? It would if it received a chemical memo saying that its service in its current tissue is no longer required, and that it should head to its new assignment in the fat department.
So if some fat cells were once cells in preferable kinds of tissues, how can we order them to go back? One of the most effective ways to send that kind of message is with exercise. According to Dr. Robert Lustig, Professor of Pediatric Endocrinology at University of California, San Francisco, the reason exercise treats obesity is not because it “burns” calories. “That’s ridiculous,” he says. “Twenty minutes of jogging is one chocolate chip cookie. I mean you can’t do it. One Big Mac requires three hours of vigorous exercise to burn off. That’s not the reason exercise is important.”280 Exercise is important because it generates signals to transdifferentiate your fat.
Exercise works at least three ways: 1) It increases insulin sensitivity, so you need less insulin to get sugar out of the bloodstream. This allows your insulin levels to drop, which tells your fat cells to slow down the conversion of sugar into more fat. 2) It reduces the stress hormone cortisol. Cortisol packs fat around organs (as opposed to under the skin) where it produces lots of pro-inflammatory chemicals, which in turn tell the body to produce still more fat. And 3) Exercise makes blood sugar levels drop, and with it the potential for AGEs and the sugar-induced inflammation that blocks healthy body-building signals.
down? Once fat cells store energy, they guard it jealously, reluctant to give it up. But when you convert fat to muscle, you rev up your metabolism, which drains fat cells. What’s more, fat cells can undergo the same kind of cellular suicide that tumor cells can, called apoptosis.
This discovery that so many cellular transformations are occurring has unsettled the medical community, which must now abandon the old notion of a cell as something created to be a lifelong member of one particular cellular species. This model grossly underestimates the cell’s protean nature. Just as genes change in reaction to what we eat, think, and do, cells change their internal construction too, dedifferentiating from a mature phase back into the immature, pluripotent stage of cell life. And then, from the pluripotent stage, they can be instructed to redifferentiate back into the original, or even be recruited into another type of tissue altogether. The culture medium scientists use for inducing all those cellular transformations is not an alien brew of unnatural chemicals, but rather a full complement of vitamins, amino acids, and sugar, plus different mixtures of naturally occurring growth factors and hormones that a healthy young body normally manufactures. The readiness and completeness with which cells respond to such instructions suggests that these conversions are an integral aspect of healthy physiologic function.281