One the most informative articles I've read about 'killer' and 'benign' belly fat.

Source Discover Magazine

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Visceral fat lies deep inside the abdomen, surrounding vital organs like the liver, heart, intestines, and kidneys, as well as hanging, in a separate double flap, off the ends of the stomach like an apron. In lean people, the flap, known as the omentum, is thin enough to be seen through (by
someone in a position to have a look, that is). In obese people it may be inches thick, fused, and "hard like cake," according to Edward Mun, now director of bariatric surgery at Faulkner Hospital in Boston; he is the surgeon who removed part of Garofolo's omentum. Packed around the organs is another type of visceral fat, called mesenteric.

The abdominal region harbors still another kind of fat, which lies outside the abdominal wall, just under the skin. This subcutaneous, or peripheral, fat tends to be soft and flabby; you can pinch or grab it. It has two compartments, the deeper of which is thought, like visceral fat, to have negative effects on health. The superficial layer may cause cosmetic distress in women who get a buildup of it as they age, but from a medical perspective it is considered benign. Subcutaneous fat also appears outside the abdominal area, on the lower body—the hips, buttocks, and upper thighs. There it is not only benign but actually beneficial.

"Peripheral fat is, in reality, good fat," explains Osama Hamdy, director of the obesity clinic at the Joslin Diabetic Center.

Before menopause, women tend to have more good fat than men do. One interpretation holds that, through most of human evolution, visceral fat was useful for short-term storage—it accumulates quickly and is released quickly—for the benefit of male hunters who needed quick access to energy. Subcutaneous fat, in contrast, was meant for long-term energy storage, for the benefit of the (often female) gatherers who had to wait a long time between meals. Subcutaneous fat is less active metabolically than visceral fat. "It's like a big bucket," Smith says. "It locks the fat in." Put another way, it keeps accepting excess caloric energy that might otherwise end up in the abdomen. Jean-Pierre Després, director of research in cardiology at the Laval Hospital Research Center in Quebec City, calls subcutaneous fat "an expandable metabolic sink."



http://discovermagazine.com/2007/feb/visceral-fat