A recent study in the Journal of the American Medical Association (JAMA, 2007) shows that even exercising less than standard recommendations offers some health benefits. But it was published just one month after another study found that getting beyond the standard 30 minutes of daily moderate activity brings dramatically better weight control. The emerging message of these and previous studies seems to be: the benefits of physical activity vary with how much you do.

The good news that every little bit helps comes from a study of 464 sedentary, post-menopausal women who were all either overweight or obese. The women were randomly assigned to one of four activity-level groups: three of the groups provided supervised exercise at either 50, 100, or 150 percent of the National Institutes of Health recommended physical activity, which aims for about 30 minutes five days a week. The fourth group was a non-exercising group.

The group at 50 percent exercised for an average of 72 minutes weekly. The group at 150 percent got in an average 192 minutes of weekly exercise. Participants were not instructed to cut calories. After six months, three different measurements showed all three activity groups were more fit, even in the 50 percent group that exercised the equivalent of 15 minutes five days a week. Each increase in exercise brought a greater improvement in fitness.

The JAMA study adds further support to the 2001 findings from the Women�s Health Study that those who walked even 60 to 90 minutes weekly developed about half the heart disease as sedentary women. However, in this new study, only the group exercising the longest showed a drop in blood pressure. And despite the improvements in overall fitness, none of the groups lost weight. All three exercise groups did, however, show over an inch drop in waist measurement despite lack of weight loss.

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The other recently published study found that it may take a lot of exercise to affect weight loss. The study randomly assigned 202 men and women ages 25 to 50 to either a standard behavior change weight reduction program or one that required more exercise. Participants were about 30 to 70 pounds overweight. Both programs included a low-calorie diet. The standard program instructed members to burn about 1,000 calories per week (about 30 minutes a day of moderate activity, such as walking); the high-exercise group was asked to burn about 2,500 calories per week (about 75 minutes of exercise a day).

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All study participants exercised on their own and for 18 months they met regularly with a group leader. At six months, weight loss between the two groups was essentially the same. After that, even though the treatment program lasted 18 months, the standard group began regaining weight and the high-exercise group did not. At 12 months and 18 months, the high-exercise group had lost more weight, even though many in the high-exercise group did not reach the 75 minutes per day goal.

After one year without group support, average exercise levels were roughly the same for both groups and the "high-exercise group" had lost only slightly more weight than the standard group. However, there remained a link between participants who exercised the most and weight loss. Those who were exercising the equivalent of at least 75 minutes five days a week lost more than 10 times as much weight as those exercising less than 30 minutes five times a week. Participants exercising the most also showed much less weight regain.

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A variety of studies over the years have shown an association between 30 minutes of daily moderate exercise and reduced heart disease and diabetes. Some studies have shown 30 minutes of daily exercise can lead to weight loss and/or a fitter body. However, as these studies show, if you�ve been exercising and not losing weight, you may need to add another 15 to 30 minutes of activity, change what you eat, or both.