Mankind146;s secret weapon?

Yet fat tissue is not the problem here, and to castigate fat for getting too big and to blame it for high blood pressure or a wheezing heart is like a heavy drinker blaming the liver for turning cirrhotic.

In fact, like the drinker8217;s liver, fat tissue also has our best interests at heart.

8220;Obesity is not due to any defect in adipose tissue per se; it8217;s an issue of energy balance, where the excess energy is stored in adipose tissue,8221; said Bruce M Spiegelman of the Dana-Farber Cancer Institute in Boston.

8220;If you had no fat cells, no adipose tissue, you8217;d still be out of energy balance, and you8217;d put the excess energy somewhere else,8221; he said, at which point really bad things can happen. Consider the lipodystrophy diseases, rare metabolic disorders in which the body lacks fat tissue and instead dumps its energy overruns in that jack-of-all-organs, the liver, causing extreme liver swelling, liver failure and sometimes even death.

8220;Some adipose tissue is a good thing,8221; said Barbara Kahn, chief of the endocrinology, diabetes and metabolism division at Beth Israel Deaconess Medical Center, at Harvard.

Indeed, evolutionary biologists have proposed that our relative plumpness compared with our closest nonhuman kin, the chimpanzee, may help explain our relative braininess. Even a lean male athlete with a body fat content of 8 per cent to 10 per cent of total body mass is still a few percentage points more marbled than a wild male chimpanzee, and scientists have suggested that our distinctive adipose stores help ensure that our big brains will be fed even when our cupboards go bare.

Scientists who study fat emphasize that its bland and amorphous appearance notwithstanding, our adipose depots represent highly specialized organs, as finely honed to the task of energy storage as muscle is built for flexing.

Our body fat is made of some 40 billion fat cells, or adipocytes, and their supportive matrix, with most of the bulk stashed under the skin but also threaded viscerally, around and between other organs. Each fat cell is essentially a bouncing balloon filled with those greasy lipids we call triglycerides, three fatty acid chains of mostly carbons and hydrogens arrayed in high-energy configurations.

In most body cells, the watery cytoplasm, where the labor of proteins takes place, accounts for maybe 70 per cent of the cell8217;s volume, with another 10 per cent given over to the nucleus, seat of the cell8217;s DNA.

In a fat cell, by contrast, lipids are king, queen and bishop, and the checkerboard, too. They fill more than 95 per cent of the adipocyte volume.

Yet for all its lipid density, the average fat cell is ever primed to hoard more and swell to several times its cellular waistline of yore. Most weight that we gain and lose in life is the result of our existing fat cells growing and shrinking, absorbing and releasing energy-rich lipids as needed, depending on our diet and exercise regimens of the moment.

But when exposed to chronic caloric overload, fat cells will initiate cell division to augment the supply; and because fat cells, like muscle cells, rarely turn over and die, those new lipidinous recruits will be your helpmeets for life.

Fat is no rutabaga. It is dynamic and mercantile, exchanging chemical signals with the brain, bones, gonads and immune system, and with every energy manager on the body8217;s long alimentary train.

8220;We used to think of an adipose cell as an inert storage depot,8221; Dr Kahn said. 8220;now we appreciate that it is an endocrine organ,8221; that like the thyroid or pancreas, secretes hormones to shape the behavior of other tissues far and wide.

Squashed to the side a fat cell8217;s cytoplasm may be, but it nevertheless spins out a steady supply of at least 20 different hormones. Key among them is leptin, an essential player in reproduction.

Scientists suspect that a girl enters puberty when her fat stores become sufficiently dense to begin releasing leptin, which signals the brain to set the pulsing axis of gonadal hormones in motion.

Fat also seems to know when it is getting out of hand, and it may resist new personal growth.

Dr Spiegelman and others have shown that with the onset of obesity 8212; defined as 25 or more pounds above one8217;s ideal weight 8212; the fat tissue starts releasing potent inflammatory hormones. That response is complex and harmful in the long run. But in the short term, said Dr Spiegelman, 8220;inflammation clearly has an anti-obesity effect, and it may be the body8217;s attempt to restrain further accumulation of adipose tissue.8221;