Having a little paunch is just no good with a Speedo or bikini. Health-wise, it's none too pretty, either.

That bulge is the outward sign of a deeper problem: visceral fat, a kind of biological monstrosity that, in excess, wreaks havoc on the body, raising the risk for heart disease, diabetes, possibly even some types of cancer.

Lying deep inside the body, wrapping around the liver and other major organs, visceral fat acts like a kind of organ itself — spewing out bad hormones and squashing the production of good ones. It sets up the body for sickness as the years roll by and additional fat accumulates.

"Visceral fat is very bad for you," says Richard N. Bergman, a professor at the University of Southern California's Keck School of Medicine. "It seems to have a more negative outcome on health than overall fat."

The evidence now is so compelling that some experts suggest it's time to forget about scales and weight loss and focus on waists and "inch loss."

Luckily, visceral fat doesn't appear to be a particularly stubborn enemy. Health experts have discovered that consistent, moderate exercise by itself appears to help the body rid itself of vast amounts of deep abdominal fat.

This emerging science carries a message for consumers: Measure your waist circumference. And reduce it if need be. Doing something about that paunch could help save your life.

Recent studies on visceral fat help explain a well-established fact: that having a pear shape is more healthful than having an apple shape. A pear shape is caused by subcutaneous fat resting just under the skin. Apple is caused by the deep, visceral fat. What this means is that although both types of people — apple and pear — can be overweight, the person with the apple shape has more health risks.

Most people gain abdominal fat with age, but research shows the tendency to put on weight around the middle may be inherited. A study published last month in the Proceedings of the National Academy of Sciences identified particular genes that appear to dictate how fat develops and where it's stored.

Meanwhile, the evidence for visceral fat's ill effects is mounting. In research published in November in the Lancet, doctors concluded that a person's waist measurement is a more accurate predictor of heart attack than the body mass index, or BMI, which is a weight-to-height ratio.

Analyzing data from 27,000 people in 52 countries, the scientists found that BMI measurements were only slightly higher among people who had had heart attacks compared with those who hadn't. But heart attack sufferers — of all ethnicities — had a much higher waist-to-hip ratio (a measurement that reflects abdominal fat) compared with those who hadn't.

Other studies have linked visceral fat to metabolic syndrome — a grouping of risk factors, such as high cholesterol and high blood pressure, that can precede diabetes and heart disease.

Additional illnesses may be influenced by excess abdominal weight too. A Kaiser Permanente study presented earlier this year showed that people with the most abdominal fat were 145 percent more likely to develop dementia compared with people with the least amount of ab fat.

Experts aren't sure why fat can be bad in one area of the body and yet not so bad in others. But they have two strong theories. One has to do with what visceral fat does. The other has to do with where it is.

Today scientists know that fat is more than just blubber. Fat cells were once thought of as inactive storage units containing a droplet of oil — the fat — that expand in a person who is gaining weight and shrink with weight loss. Now researchers have adopted a more complex picture of fat cells as mini-endocrine factories that produce a range of good and bad substances.

"Once we got beyond the bag-of-fat concept, we found there were a lot of things going on with those cells," says Philip A. Wood, director of genomics at the University of Alabama-Birmingham and author of the book "How Fat Works."

In 1994, researchers identified a hormone, leptin, which is made by fat cells to signal a feeling of fullness. Researchers now think that leptin goes down in people with excessive abdominal fat — leading people to eat more.

Probably the best news about visceral fat: It's not all that hard to lose. Sit-ups and liposuction won't work, but studies show that regular diet and exercise can lead to a substantial drop.