(Nov 3) NOT all fats are created equal, it seems.

There are two types of fat on the human body, say doctors here - the fat just below the skin called subcutaneous fat, and its more worrisome cousin, visceral fat. The first type is easily noticeable - it's the fat that gives you double chins and flabby arms. The second type, however, is buried beneath the muscles and isn't as visible.

'Visceral fat, which is found mostly around the abdomen, is more worrying because it surrounds vital organs. Excess visceral fat can lead to heart disease and a host of other ailments,' says Dr Goh Ping Ping, senior consultant and cardiologist at Changi General Hospital.

Visceral fat is the type of fat that is metabolised by the liver, which turns it into cholesterol that circulates in the blood. 'Bad' cholesterol or LDL, collects in the arteries where it forms plaque, a waxy substance that narrows the arteries.

The bad news about visceral fat is that it can accumulate quickly. One study done in the US found that after just eight weeks of no exercise, a group of overweight men and women showed significant increases in visceral fat.

The good news about visceral fat, however, is that regular moderate physical activity can help prevent it, and regular vigorous physical activity can help get rid of it.

'Visceral fat is often associated with obesity. This is excess fat that is consumed in the diet, and it's a reflection of our lifestyle,' says Dr Goh, who feels Singaporeans in general are far too sedentary.

Being overweight increases the risk of visceral fat, but it is not only what you weigh but what you eat that contributes to visceral fat.

According to Dr Goh, the existing measurement for obesity - the body mass index or BMI - may not be an accurate way of determining how much visceral fat one has.

'Conventionally, the BMI is the standard form of measurement, but we are realising now that a heavyset person may not have a lot of fat. His weight could be due to muscle mass instead,' explains Dr Goh.

As a result, doctors are now relying on waist measurements to get an indication of how much visceral fat there is on a person. 'A person's waist circumference gives a clue to the amount of visceral fat in the body. Anything in excess of 90cm for men and 80cm for women is dangerous,' warns Dr Goh.

Even then, the only effective way to locate and measure visceral fat is by magnetic resonance imaging or MRI, which uses magnetic fields and radio waves to take a picture of the inside of the abdomen.

According to Dr Goh, a person's genetic makeup can be responsible for the amount of visceral fat he carries. Nevertheless, research has shown that both diet and the level of physical activity contribute to the level of visceral fat in the body.

'Some are genetically programmed, but generally, people who consume large amounts of saturated fat and those who perform very little or no physical exercise are likely to have higher stores of visceral fat,' says Dr Goh.

Saturated fat is hard fat, like lard, butter or fat on meats. Alcohol, too, gives excess calories that can be converted into visceral fat. In our nation of buffet lovers, this doesn't bode well.

Menopausal women in particular should take note, since many women experience a natural increase in obesity following menopause, especially in the intra-abdominal area.

So what can be done for those who already have pear-shaped bodies?

'Lifestyle modification is always the first line treatment of choice. We encourage overweight people to change their diet and adopt an exercise regime, because visceral fat is not something that you get rid of for good - it will come back, if you revert to your old lifestyle,' says Dr Goh.

Research has shown that people whose diets contain polyunsaturated fats have less visceral fat. Polyunsaturated fats are found in high concentrations in sunflower, corn and soybean oils, as well as in fish.

Exercise is also central to the battle against bad fats.

'It doesn't have to be very vigorous for a start. Just doing things like walking or swimming can help prevent visceral fat from accumulating,' advises Dr Goh.

Building muscle, too, through weight training or other resistance exercises, may help, since muscle burns calories and helps to maintain one's metabolic rate. The more muscle one has, the bigger the body's engine, and the more likely one will be able to burn fat.

Isn't there an easier way, you ask? What about medication?

'We don't usually prescribe drugs to combat obesity, mainly because there are side effects to these drugs and the results are not permanent. Medication will be a last resort. Also, a lot of patients who are obese have high blood pressure or diabetes, so they are already taking a lot of medication,' explains Dr Goh.

Omron's Body Composition Monitor (Model HBF 361/362), which measures visceral and subcutaneous fat levels as well as metabolic rate, is available at retail stores in Singapore