Science says soy supplements don't help asthma after all

Sayuri Yoshii of Japan uses an inhaler as she recovers after skating to fifth place in the Women’s 1000m at the ISU World Single Distance Speed Skating Championships. Doug Pensinger/Getty Images

Soy supplements don’t improve lung function of people with asthma despite previous research showing a benefit, according to a study.

The results of the research, published in the Journal of the American Medical Association (JAMA), highlight the importance of focusing on overall health to manage disease rather than individual strategies such as increasing soy consumption,.

“You are what you eat, but that’s a whole constellation of foods, not just a single food or a single component of a food,” said Lewis Smith, professor of medicine at Northwestern University Feinberg School of Medicine. “Instead of focusing on supplements, we should be taking a more holistic approach.”

Nutritional supplements, a multi-billion dollar industry, are used to treat and prevent disease and to optimise health although there’s not always data proving effectiveness.

However, there is evidence that supplements for soy isoflavone — plant-based compounds in food such as tofu and edamame — protect against hot flashes during menopause and osteoporosis.

Smith and colleagues previously noticed that asthmatics taking soy isoflavone had better lung function.

“If you look at people who consume more soy products, mostly in Japan and parts of China, they actually have less asthma,” said Smith. “That could be due to many different factors, but there was enough epidemiological and biological evidence data to support looking at this association.”

The latest study explored the effects of soy in 386 adults and children aged 12 or older with poorly controlled asthma.

“We found that the supplement, though able to increase blood levels of the key soy isoflavone genistein, did not improve lung function, symptoms or measures of inflammation in these individuals,” Smith said.

Smith said other factors may have been at play for previous studies, such as diet and lifestyle patterns, eating less meat or exercising frequently.

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