Healthy but obese adolescents display abnormal responses to tests of blood vessel function, but after a short course of exercise their test results match those of lean youngsters, even though they remain heavy, according to
a new study in the May 19, 2004 issue of the
Journal of the American College of Cardiology.
"We were able to essentially normalize endothelial function in a short period using the exercise training program that we administered. That's the exciting part. It's a good news story," said Daniel J. Green, PhD, from the University of Western Australia in Crawley, Australia. "This paper adds another piece to the jigsaw puzzle which says that exercise is beneficial not only because it may improve your risk factors, like lipids and blood pressure, but it also probably has a direct effect on your blood vessels that makes them more fit."
The study involved 19 obese adolescents (age 12 to 15 years, average weight 96.4 kg, 212 lbs.), who were apparently healthy nonsmokers with normal blood pressure and cholesterol, and who weren't on any medications. Compared to a matched group of 20 lean controls, the obese adolescents displayed impaired flow mediated dilation, which is a measurement of how blood vessels respond to changes in blood flow. Impaired flow mediated dilation is considered an early warning sign of atherosclerosis.
But after an eight-week course of one-hour exercise sessions three times per week that used stationary cycling and strength training with light weights, the blood vessel responses of the obese youngsters matched those of their lean counterparts. Dr. Green pointed out that although blood vessel response is increasingly seen as an early step in the development of artery disease, the adolescents in this study did not have overt signs of atherosclerosis. He also noted that researchers have not demonstrated that improving blood vessel responses will prevent heart disease.
Dr. Green said it is important to note that the obese subjects did not lose weight, but their body composition changed. He said it is time to rethink both the type of exercise recommended for obese individuals and how the results of an exercise program are measured. The researchers, including lead author Katie Watts, BSc(HONS), used an X-ray technique known as DEXA analysis (dual-energy X-ray absorptiometry), which can differentiate between body fat and muscle mass.
"We found a decrease in percentage body fat, particularly from the worst place to have fat, which is the viscera, around the internal organs. We found a decrease in abdominal obesity in this group. And the reason that they didn't lose weight, even though they lost body fat, is that their lean muscle mass went up. So we were really seeing a very beneficial change in the composition of the body, without changes in gross measures like body weight," Dr. Green said.
Dr. Green said the results suggest that focusing on weight alone may be a disservice to obese individuals. He said they may become discouraged when exercise doesn't produce rapid weight loss, even as beneficial changes are occurring. In this study, the obese participants did not change their usual diets.
Half the subjects in this study exercised for eight weeks and then resumed their normal activities, while the other group waited eight weeks before taking the training course. The results showed that while the benefits of exercise can be felt quickly, they may disappear just as quickly.