Exercise alone, even without weight loss, can improve cholesterol levels and perhaps your heart, researchers have found.

It doesn't take strenuous exercise to alter cholesterol levels to benefit your heart. Modest exercise can help by making cholesterol less damaging to the arteries, even if levels in the blood remain unchanged.

Cholesterol is an energy-rich fat that attaches to protein particles, circulates through the bloodstream and nourishes tissues. Workouts carry health benefits but using exercise to improve cholesterol wasn't considered a main route.

Jogging 20 miles a week significantly increased "good" cholesterol

Earlier studies looking at the effects of workouts on cholesterol may have missed the link because chemical measurements were less accurate at the time.

Researchers at Duke University have found exercise can in fact affect cholesterol by lowering the number and size of the particles that carry the fat through the bloodstream.

"We showed that increasing amounts of exercise increased the size of the (protein) particles carrying both the good and the bad cholesterol," said the study's lead author, Dr. William Kraus of Duke.

Exercise changed the cholesterol profiles measured in blood

Shape of cholesterol protein makes it dangerous

When small, dense proteins (LDL or "bad" ones) carry cholesterol, it appears more likely to clog arteries compared to large, fluffy carriers (HDL or "good" variety).

The study in Thursday's New England Journal of Medicine found people who exercise develop the bigger particles, even if the total amount of cholesterol stays the same.

Kraus' team looked at 111 sedentary, overweight men and women who were randomly assigned into three exercise groups for up to eight months. One group walked the equivalent of 20 kilometres a week, the second jogged 20 kilometres a week and the third jogged 30 kilometres a week.

All participants, including a nonexercising control group, were encouraged to keep their weight constant to allow investigators to look at the benefits of exercise alone.

Those benefits were most noticeable in those who were the worst off – the heaviest people who had low levels of "good" cholesterol in the first place.

The amount of exercise appeared to matter more than the intensity, Kraus said.

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In a commentary that accompanied the study, Alan Tall of Columbia University said the study offers hope for those who find it easier to exercise than to lose weight.

"We were actually surprised that the individuals who did not exercise deteriorated as rapidly as they did in measurements of blood cholesterol, weight gain and overall health," he said in a release.

He added a little exercise is better than none at all. But it took the equivalent of jogging 30 kilometres every week to significantly boost "good" cholesterol levels.