Amid all the hooplah over oat bran and fish oil, synthetic fats and cholesterol-lowering drugs, one of the simplest, safest, least expensive and most significant cholesterol-improving strategies has been sorely neglected.

"Regular exercise makes quite an important contribution to improving your cholesterol status," says Peter Wood, an associate director of the Stanford Center on Research in Disease Prevention. "Yet in the big flurry of interest in cholesterol that's gone on over the last few years, there's been a relative lack of emphasis on . . . keeping active and being lean."

One reason exercise has taken a back seat to diet and drugs is that it's harder to study the effects of exercise than the effects of drugs. "You can't have a placebo exercise," Wood notes. Also, food and pharmeceutical companies fund a substantial portion of cholesterol research.

While diet modification is still considered the most important lifestyle change most people can make to improve their cholesterol status, recent research shows that regular aerobic activity:

Raises the level of "good" HDL cholesterol.

Lowers the triglyceride level.

Improves the total cholesterol/HDL ratio.

Slightly lowers the level of "bad" LDL cholesterol.

"There's still some controversy over whether the benefits of exercise are more due to the muscle contraction itself or to the fact that if you exercise you tend to be slim," says Wood. "But from a practical point of view I'm not sure it matters. You can't find people who exercise a great deal who are fat."

And excess fat puts people at an increased risk of having unhealthy cholesterol levels. Emerging studies indicate that it's not body fat alone that contributes to cholesterol problems but how that body fat is distributed. People tend to store excess fat in different places, determined by heredity and sex hormones. This is why men are more likely to have pot bellies and women "thunder thighs."

"We're finding that a small amount of fat in the abdomen is worse than a large amount of fat in the thighs and hips in terms of cholesterol status," Wood notes. One theory points to the way blood circulates in the body. When it leaves the abdomen, it goes directly to the liver, taking some fat particles with it. The result may be that the liver puts out more cholesterol-containing lipoproteins.

This may explain why "apple-shaped" men are at greater risk of heart disease than "pear-shaped" women.

Ridding the body of excess fat, particularly abdominal fat, is vital to improving your cholesterol profile."Today, most people agree that weight loss won't work in a permanent sense unless exercise {is} involved," Wood notes.

But helping people lose fat is just one way exercise improves cholesterol levels. "Recent research suggests that passing blood through a muscle that is exercising improves it," Wood says. "Presumably, if you have big muscles and exercise a lot, you would greatly improve your blood."

Exercise has "a separate and additive effect independent of weight loss," says cardiologist Arthur Leon, a professor at the University of Minnesota School of Public Health. In his study, men who exercised without losing weight experienced a 12 percent rise in their "good" HDL levels; men who lost weight without exercise also experienced a 12 percent rise in HDL levels. But men who both exercised and lost weight showed a 22 to 24 percent elevation.

In addition to raising the "good" HDL, exercise slightly lowers the "bad" LDL, says Paul D. Thompson, a cardiologist at Miriam Hospital in Rhode Island and associate professor of medicine at Brown University. "When a sedentary person starts to exercise regularly, the fluid volume in their bloodstream expands. So just by dilution alone, it dilutes out the LDL values."

Also, the primary fuel for endurance exercise is fat. Exercise helps break down trigliceride particles and remove the fat from them. Some cholesterol from these trigliceride particles gets passed to the HDL particles and raises the HDL cholesterol levels, Thompson says.

"The average American male has an HDL level of 45," he notes. "A distance runner has a level of about 65. For every one to two point increase in your HDL level, there's a 2 to 4 percent reduction in your risk of heart disease."

"In a high percentage of cases, people who have heart attacks have either a low HDL cholesterol level or a high total cholesterol/HDL ratio," says physician Kenneth Cooper, executive director of the Aerobics Center in Dallas. These are the two factors that can be most directly improved, he says, by raising your level of aerobic fitness.

While exercise's effect on cholesterol is complex and will vary with each individual, Cooper sums up these facts in his book, "Controlling Cholesterol":

1. Regular, brisk walking over a period of just a few months can significantly increase your HDL levels.

2. Moderate exercise (20 to 30 minutes, three times a week) may result in a significant increase in HDL levels.

3. There's a direct correlation between increasing levels of physical fitness and healthier HDL levels, and ratios of total cholesterol/HDL cholesterol.

4. Being physically sedentary may significantly lower a person's HDL cholesterol.

To improve your cholesterol profile, perform an aerobic exercise such as brisk walking or jogging three to four times a week for a minimum of 20 to 30 minutes for each session, says Cooper, who advises people over 40 or those who have any risk factors of coronary disease to consult a physician before beginning a vigorous exercise program.

Bodyworks appears on alternate Tuesdays.