Although previous studies had pointed towards a link between increased soy intake and decreased asthma symptoms, a new clinical trial has shown that taking soy supplements does not improve one’s asthma symptoms.

The previous studies had been population based, whereas the clinical trial was “multicenter, randomized, double-blind, [and] placebo-controlled.” Lewis J. Smith, MD of the Feinberg School of Medicine in Chicago called the test results “disappointing” but said they show the limitations of cross-sectional studies.

Bradley Chipps, MD from the Respiratory Disease Center in Sacramento said, “Would I have loved this to have been positive? You bet I would, because we would have been able to say, ‘Here is an absolutely safe dietary supplement you can use to control your asthma at a much cheaper price than expensive asthma medication.’ It didn’t work, but it’s important that this hypothesis was tested.”

To test the hypothesis, 193 patients were given soy supplements and 193 were given a placebo for a period of 24 weeks. Unfortunately, the results showed no difference in asthma symptoms between the two groups. The only change was that the placebo group showed an improvement in “forced vital capacity” (how much air one can breath out after inhaling as much as they can). But the researchers concluded this was “not clinically meaningful.”

Scientists haven’t completely given up hope that soy supplements could help asthmatics. Some have wondered if perhaps certain ethnic groups would be more likely to respond positively to the soy supplements, and others feel it might be worth testing if the supplements are more helpful to children.