Researchers Say Regular Exercise Does Not Lead to a Healthier Diet

Newswise — Despite the common belief that regular exercise brings about healthy changes in diet, a 16-month study conducted by University of Kansas researchers disproves the popular idea.

Joseph E. Donnelly, KU professor of health, sport and exercise sciences, and Debra Sullivan, associate professor of dietetics and nutrition at the KU Medical Center in Kansas City, Kan., joined researchers from the University of Colorado to publish the study in the November issue of the American Journal of Clinical Nutrition. Assisting the group were Dennis J. Jacobsen, research associate, and Erik P. Kirk, graduate teaching assistant, both in KU's Life Span Institute.

The researchers' conclusions showed there were no significant differences for men or women between the exercise and control groups in fat, carbohydrate or protein intake over the course of the study.

"It is a popular notion that people change their eating habits and change them for the better when they exercise," Donnelly said. "The general public believes that everyone reduces fat and increases carbohydrate intake automatically when exercising, but this spontaneous change to a healthy diet didn't happen."

Major health organizations generally recommend diets that increase the intake of complex carbohydrates and decrease the intake of fat to diminish the risk of cardiovascular disease and diabetes, Donnelly notes in the study.

Called the "Midwest Exercise Trial," the study started at the University of Nebraska-Kearney in 1996 and was transferred to Lawrence in 1997 when Donnelly and Jacobsen joined the KU faculty. The study was funded with $2.4 million from the National Institutes of Health.

Participants were recruited from UNK, KU and their surrounding communities. Of the 131 people selected to participate, 74 completed the study. Participants were 17 to 35 years old and were overweight to moderately obese. In addition, participants were free of chronic disease such as diabetes, did not have high blood pressure or high cholesterol, were nonsmokers and led sedentary lifestyles.

Participants were divided into exercise and control groups. For the exercise group, physical activity consisted of walking on a treadmill five days a week. Alternate activities, such as stationary biking or using stationary elliptical trainers, were allowed for one day a week. Exercise by participants was performed under direct supervision of researchers.

The exercise group progressed from 20 minutes of exercise per day at the beginning of the study to 45 minutes at six months. The intensity of the exercise progressed from 60 percent of heart rate reserve -- the difference between maximum heart rate and resting heart rate -- at the beginning to 75 percent at six months, with that level of exercise maintained for the remainder of the study. This level of exercise is recommended by the College of Sports Medicine for programs designed for weight reduction, according to the study.

The exercise group maintained its normal dietary intake, which was assessed six times during the study. Each assessment consisted of a two-week period during which participants were observed eating in a KU cafeteria.

Meanwhile, the control group underwent the same testing as the exercise group, except for testing relating to the 16-month exercise program. They were instructed to maintain their normal physical activity and eating habits throughout the study.

Donnelly was not surprised by the results.

"I had no reason to suspect that the results of this particular study would be different from other studies I conducted," he said. "In weight management, many people think they can exercise and eat anything they want. You have to consciously change your diet along with the exercise. The exercise industry is known to overstate the importance of exercise in relation to diet."

Sullivan added, "I think it's easier for people to believe they can eat whatever they want as long as they exercise. If we read the ads in magazines or watch television, we are being told that all we have to do to lose weight is to exercise."