New research suggests people who keep fit counter some of the ill effects of weight gain.

Losing fitness or packing on fat with age can both be bad for the heart - but avoiding either one of those fates may protect the ticker, a study published on Monday suggests. US researchers found that of more than 3,100 healthy adults they followed, those who improved - or simply maintained - their fitness levels were less likely to develop high blood pressure, high cholesterol or other well-established heart disease risk factors. Similarly, people who maintained their weight had fewer of those red flags than people who became heavier over time. That may sound logical, but part of what's new in the findings, researchers say, is that changes in fitness and "fatness" each appeared important on their own.

In general, people who kept their fitness levels over time seemed to counter some of the ill effects of weight gain. And dips in fitness levels weren't as bad if a person lost some excess body fat.

The results suggest that protecting heart health is not as hard as some people think, according to lead researcher Duck-chul Lee, of the University of South Carolina in Columbia.

That is, just maintaining your weight and fitness levels as you age may be enough to see benefits.

"If you're overweight, losing weight and improving your fitness may be the best combination," Lee says. "But that's very challenging."

For many people, "maintenance" may be more achievable, Lee says.

The study, published in the Journal of the American College of Cardiology, included 3,148 men and women in the Dallas area who were in their early 40s, on average, at the outset.

Over six years, they developed high blood pressure at a rate of 4 percent each year, high cholesterol at a rate of 3 percent per year and so-called metabolic syndrome at a rate of 2 percent per year. (Metabolic syndrome refers to a collection of risk factors for heart disease - including high blood pressure, unhealthy cholesterol levels, abdominal obesity and high blood sugar.)

But people who kept up or improved their fitness levels - as measured during treadmill tests - had lower odds of developing those heart risk factors.

Their risks of high blood pressure or high cholesterol were 26 percent to 30 percent lower, versus people whose fitness levels declined. And their risk of metabolic syndrome was 42 percent to 52 percent lower.

Similarly, when people increased their percentage of body fat over time, they were more likely to develop heart risk factors.

For each 1 percent increase in body fat, the odds of those risk factors climbed anywhere from 3 percent to 8 percent.

But in general, people who gained weight stayed healthier if they kept up their fitness levels. And if overweight people shed some fat, they countered some of the negative effects of waning fitness.

The bottom line, according to Lee, is that people who are active should stay active. Even if you don't see a benefit on your bathroom scale, you'll stay fit.

"If you're already exercising, keep it up, and maybe increase the intensity if you can," Lee says.

If you're sedentary but healthy, he says, you can safely take up moderate exercise like brisk walking. Lee adds, though, that people who are obese or have chronic health conditions should talk to their doctors first.

"It's the sedentary people who will get the most benefit from exercise in a short time," Lee says.

He was, however, referring to the benefit of improved fitness. Overweight people often fail to see the pounds fly off when they first start exercising - possibly because they are hungrier and start eating more.

Don't get discouraged by that, Lee says. You can improve your cardiovascular fitness even without shedding the extra body fat. One way to tell if your fitness is improving, Lee says, is to simply notice how you feel when you go about your normal exercise routine; if it's getting easier, you're getting fitter.

To actually lose weight, diet changes are needed as well.

"Most people will lose weight with exercise if they also pay attention to the calories they're taking in," Lee says.