DURHAM, N.C. -- A preliminary study by Duke University Medical Center researchers indicates that moderate exercise alone can improve cholesterol levels and reduce the percentage of body fat in moderately obese people, even if the exercise program does not lead to weight loss.
The results of the recently completed pilot study are the first to demonstrate that exercise alone -- independent of weight loss or diet changes -- can cut the risks of heart disease, the researchers said. They said this should provide encouragement to millions of overweight Americans, many of whom quit exercise programs because they failed to lose weight.
The results of the three-month study by Duke cardiologist Dr. William Kraus were published Tuesday (Feb.15) in the February issue of the journal Clinical Exercise Physiology.
The study findings, which involved seven mildly obese men and women, provided the scientific basis for a recent $4.3 million grant from the National Heart, Lung and Blood Institute which will allow researchers to carry out a much larger trial. That trial, called Studies of Targeted Risk Reduction Interventions through Defined Exercise (STRRIDE), has been enrolling patients for the past year.
"This pilot study was a first attempt to isolate the effects of exercise from weight loss in a controlled fashion," Kraus said. "We designed the trial such that we can attribute all the beneficial effects to exercise alone." Kraus is confident that the ongoing STRRIDE study will confirm the results of the pilot study. Kraus added that since the changes documented by the study were consistent across all patients, the small number of patients involved does not limit researchers' ability to draw conclusions.
"We now have the data for physicians who can tell their patients that they shouldn't focus so much on the scale," said Kraus, who led the study. "These patients should not become discouraged and give up exercising, because our study shows that these patients are getting healthier even if they don't lose any weight."
Specifically, patients saw an average decline in the so-called "bad" LDL cholesterol from 122 to 104, and an average increase in the so-called "good" HDL cholesterol from 32 to 37. These changes were deemed to be statistically significant. In addition, patients saw a 4.3 percent decrease in body fat, which researchers say likely turned into muscle.
The weight of all patients remained the same during the three-month study. In fact, if patients started losing weight, researchers altered their diets to maintain a constant weight.
The patients enrolled in the trial had body mass index (BMI) ranging from 25 to 35. It is estimated that about 55 percent of Americans have a BMI greater than 25, and half of them have a BMI greater than 30. BMI, because it takes into account the height of a person, is considered the most accurate measure of obesity. It is calculated by dividing body weight (in kilograms) by the square of the height (in meters) -- a BMI of 30 is considered obese, 35 is considered morbidly obese.
The patients also had elevated cholesterol levels.
"It is important for health policy reasons to know how much exercise to recommend," Kraus said. "Physicians have always recommended exercise, but there has been no real scientific basis on how much and how intensely one should exercise."
In the trial, patients worked out for about one hour four times a week using a combination of treadmill, stationary bicycle, stair exercises and other exercise equipment. As the trial progressed, the intensity of exercises increased.
"This study shows that starting a moderate exercise program of only three months' duration -- even in the absence of weight loss -- can have significant beneficial effects on cardiovascular risk factors in overweight people with elevated cholesterol levels," Kraus said.
Not surprisingly, Kraus said, all of the patients saw a marked increase -- 11 percent -- in their exercise tolerance, which is attributable to the redistribution of body fat into muscle.
Joining Kraus in the study were, from Duke, Spencer Brown, Ph.D., Jami Norris, Carol Torgan, Brian Duscha, Connie Bales, Ph.D., and Cris Slentz, Ph.D.
Journal
Journal of Clinical Exercise Physiology