A diet high in fiber from fruit and soy foods can reduce the incidence of chronic respiratory symptoms, especially cough with phlegm production, according to data from the Singapore Chinese Health Study.

Researchers studied the details from 571 cases of incident cough with phlegm along with research information collected from 44,068 men and women who did not suffer from the respiratory problem.

The investigators said that nonstarch polysaccharides, a major component of dietary fiber, and certain noncitrus fruits, including apples and grapes, were independently associated with reduced development of cough with phlegm. The scientists administered a 165-item quantitative food-frequency questionnaire that was developed for and validated by the men and women in the study.

With ages ranging from 45-75, the participants were all permanent residents or citizens of Singapore and formed part of two major Chinese dialect groups. The researchers said that their data provide evidence that promoting a diet high in fiber and flavonoids, such as that in fruit and soy, might make an important contribution to primary preventive strategies for chronic respiratory symptoms, both in smokers and nonsmokers.