Modification of Asthma With Soy Isoflavone

Inclusion Criteria: * 18 years of age or older; * Physician diagnosed asthma; * Positive methacholine bronchoprovocation test (20% fall in FEV1 at less than 8 mg/ml) with the past 3 years; * Smoking Status: non-smoker for 6 months or longer and a less than 10 pack-year cumulative smoking history. Exclusion Criteria: * Pulmonary function FEV1\< 70% predicted pre-bronchodilator; * Other major chronic illness: conditions that in the judgement of athe principle investigator would interfere with participation in the study or history of or physician diagnosis of COPD, emphysema, or chronic bronchitis; * Medication use: current consumption of soy isoflavone supplements or oral corticosteroid use within the past 6 months OR use of an investigational treatment within the previous 30 days; * Drug allergy: known adverse reaction to genistein, other phytoestrogens, or soy products; * Females of childbearing potential: pregnant or lactating or women of appropriate ago who report the possibility of pregnancy at the time of enrollment will be screened and cannot participate if pregnant; * Non-adherence: inability or unwillingness to provide informed consent or inability to swallow study medication or inability to perform baseline measurements or completion of fewer than 5 of the 7 days of screening period diary entry or inability to be contacted by telephone; * Other exclusions: recent asthma exacerbation (within 6 weeks) or recent upper respiratory tract infection (within 2 weeks) or ch…