People are silhouetted against the sun as they exercise on the bridge over Yangon River in Yangon November 25, 2009.[Agencies]

NEW YORK - Exercise seems to simultaneously make people hungrier, yet more readily satisfied by a meal -- and differences in these responses from person to person may help explain why some exercisers shed pounds more easily than others, researchers say.

In a study of 58 overweight and obese adults who started an exercise regimen, researchers found that exercise tended to boost participants' hunger before a meal, compared with their sedentary days.

On the other hand, they were also more easily satisfied by their morning meal than they had been before becoming active.

But while both effects were generally at work across the study group, there were subtler differences between participants who were more successful in their weight loss and those whose extra pounds stubbornly hung on.

In general, exercisers who did not meet their expected weight loss were both hungrier after fasting -- that is, right before breakfast -- and throughout the day, compared with their hunger ratings at the study's start.

In contrast, those who were more successful in shedding pounds generally saw their pre-breakfast appetites increase after becoming active. But they were not hungrier throughout the day.

"The reason that some people are more successful (at weight loss) could be due to a lesser increase in appetite and the prevention of an increase in food intake," lead researcher Dr. Neil King, an associate professor at Queensland University of Technology in Brisbane, Australia, told Reuters Health in an email.

But the bottom line for new exercisers, he said, is that they should not throw in the towel if they start feeling more hungry than normal -- or fail to shed as many pounds as they'd been hoping.

Other research shows that exercise has health benefits -- like improved cardiovascular fitness, and lower blood pressure and cholesterol -- even if weight loss is modest.

For the current study, published in the American Journal of Clinical Nutrition, King's team had 58 overweight men and women go through a 12-week supervised exercise regimen designed to burn 500 calories per session.

At the beginning and end of the study, participants were given a breakfast of cereal and toast, and were asked to rate their hunger before the meal, immediately after and throughout the rest of the day.

After 12 weeks, 32 participants had lost the expected amount of weight based on the calories they burned during exercise; 26 had not. On average, both groups showed a revved up appetite before breakfast on week 12, but daily hunger was greater in those who had not lost a substantial amount of weight.

Both groups of exercisers, though, seemed to be more readily satisfied by their breakfast than they had been before becoming active.

It's not clear why these two different appetite effects arise from exercise. But physical activity, while spurring hunger, may also boost the sensitivity of the body's fullness-signaling system, according to King's team.

"The key messages," King said, "are exercise is good for you, don't expect unrealistic weight loss and don't give up exercising just because of lower-than-expected weight loss."