Research on Exercise

Duke University Medical Center researchers have demonstrated that exercise —without accompanying weight loss —has a positive impact on improving cholesterol levels.
 
Also, they report that it is the amount of activity, and not necessarily any changes in fitness or intensity of exercise, that is important for cholesterol improvement. In the process of their studies, the Duke researchers also demonstrated that the standard lipid panels used by doctors to measure the so-called LDL (bad) and HDL (good) forms of cholesterol do not necessarily provide the most accurate information in determining your risk of developing heart disease.
 
The results of the Duke study, published on Nov. 7, 2002 in the New England Journal of Medicine, show that exercise has a positive effect on the number and size of the particles that carry cholesterol through the bloodstream.
 
Cholesterol, an energy-rich fat, or lipid, must attach to protein particles in order to circulate throughout the bloodstream and nourish tissues. This combined lipid-protein unit is known as a lipoprotein, and abnormal levels of these lipoproteins have been linked to the progression of atherosclerosis (blockage in the arteries carrying oxygen to the heart) and heart disease.
 
"It appears from our study that cholesterol carried by smaller, denser protein particles appears to cause cardiovascular disease more efficiently than cholesterol carried by large, fluffy particles," said Duke cardiologist William Kraus, MD, who led the study.
 
"We showed that increasing amounts of exercise increased the size of the particles carrying both the good and the bad cholesterol," Dr. Kraus said. "By using new methods of measuring the particles carrying cholesterol, we found that some exercise is better than no exercise, and conversely, those patients in the control group who did not exercise actually showed worsening cholesterol levels."
 
According to Dr. Kraus, past studies of the effects of exercise on cholesterol have been unable to find a link because the measurements were based on the standard lipid levels, as opposed to the actual cholesterol-carrying particles.
 
"This study had to be done because there was very little scientific information indicating whether or not exercise training would have beneficial effects on cholesterol when conducted in a state-of-the art, randomized fashion, comparing individuals who exercised to those who did not," Dr. Kraus said.
 
For example, exercise guidelines issued recently by the Centers for Disease Control and Prevention and the National Academy of Science are based more on expert opinion and consensus than data gained from controlled clinical studies, Dr. Kraus said.
 
Researchers put 84 inactive and overweight men and women with high lipid levels in one of three groups:  high, intense activity equivalent to jogging 20 miles a week; low but intense activity equivalent to jogging 12 miles a week; and low, moderate activity equivalent to walking briskly for 12 miles a week. A control group did not exercise at all. The study groups included significant numbers of African American participants.
 
In order to determine the role of exercise alone, participants were not allowed to change their diet during the course of the study. Each participant followed a 2- to 3-month "ramp-up" exercise period, followed by 6 months of exercise, which was carried out on exercise bikes, treadmills, or elliptical trainers in a supervised setting.
 
Throughout the course of the study, researchers took blood samples from participants, and then used 2 new and different methods to determine the subtle and specific changes in cholesterol particle size and number. While Dr. Kraus, an ardent proponent of the benefits of exercise, believed that it would have a beneficial effect on cholesterol, he was most surprised by what appeared to happen to the control group that did not exercise during the course of the study.

"We were actually surprised that the individuals who did not exercise deteriorated as rapidly as they did in measurements of blood cholesterol, weight gain, and overall health," he said. "This is characteristic of what is happening to the American population. So if we can get these people exercising, perhaps we can prevent bad things from happening." 

Kraus believes that during the next 10 years, doctors will gradually move away from using the standard lipid profile and begin to look more closely at particle size to determine their patients' risk for heart disease. According to Dr. Kraus, inactivity ranks closely behind smoking as the greatest risk factor for heart disease, and, like smoking cessation, exercise is a lifestyle modification proven to protect the heart.
 
"Exercise can be a very powerful way of reducing risk, not only by improving lipids as our study has shown, but also by having a positive effect on glucose levels [to prevent diabetes] and mood modification [prevention of depression]," he said. "We should understand that patients do not need to lose weight or focus so much on the scale, but they do need to exercise to decrease their risk of heart disease."