Wheezy overweight women might not have asthma after all. Studies have shown an increased probability of asthma in overweight women, but researchers at the Ottawa Hospital in Canada took it further with extensive lung tests on a group of women—and suggested that many obese women are probably misdiagnosed with asthma.

What the researchers wanted to know: Can changes in body weight impact lung function in obese women?

What they did: Researchers enrolled 58 obese women in a six- to 12-week supervised program of exercise, diet, and counseling. Twenty-four of the patients had a history of asthma. All of the patients continued dieting and attending weekly counseling sessions for at least six months. They came in at the beginning, the third month, and the sixth month of the study for two lung capacity measurements: the amount of air they could exhale after taking the largest possible breath and the amount they could forcefully exhale in one second. Researchers also measured airway reactivity, the ability of the airways to change shape in response to stimuli. Poor airway reactivity is an important indication of asthma. Patients completed the St. George Respiratory Questionnaire, which evaluates quality of life, when they came in for the lung tests. Participants lost an average of 17.4 percentof their prestudy weight.

What they found: Losing weight made women breathe better whether or not they had asthma. For every 10 percent of weight loss, the two measures of lung capacity improved by about 5 percent in women with and without asthma. Airway reactivity, however, did not improve significantly—women with asthma still had asthma. The researchers say this might mean that a lot of overweight patients are misdiagnosed with asthma when they could improve their breathing by just exercising and eating healthier. So this study didn't find a connection between obesity and asthma (which doesn't mean there is no connection, of course). All of the women had a better quality of life, according to the questionnaire, at the end of the study.

What this means to you: Sometimes overweight people with asthmalike symptoms are incorrectly diagnosed with asthma. In fact, their respiratory problems may be due to "mass-loading" of the chest—which can be relieved by weight loss and exercise. Asthma does not appear to be affected by changes in body weight.

Caveats: The study did not include a control group of obese women who did not undergo the weight-reduction program.

Find out more: NIH article on the health implications of obesity: http://consensus.nih.gov

Read the article: Aaron, Shawn D., M.D., M.Sc. et al. "Effect of Weight Reduction on Respiratory Function and Airway Reactivity in Obese Women." CHEST. June 2004, Vol. 125, No. 6, pp. 2046–2052.