The Study of Soy Isoflavones in Asthma

Inclusion Criteria: * Age 12 or older * Physician diagnosed asthma * FEV1 equal or greater than 50% predicted pre-bronchodilator * At least 12% increase in FEV1 15-3 minutes after inhaling 2-4 puffs of albuterol or positive methacholine challenge (20% fall in FEV1 at less than 8 mg/mL). Either of these can be available from the previous 2 years * Currently prescribed daily controller asthma medication * Poor asthma control (at least one of the following) * A score of 1.5 or greater on the Juniper Asthma Control Questionnaire * Use of beta-agonist for asthma symptoms two or more times per week * Nocturnal awakening with asthma symptoms more than once per week * Two or more episodes of asthma symptoms in the past 12 months with each requiring at least one of the following: emergency department visit, unscheduled physician visit, prednisone course, hospitalization * Smoking status * Non-smoker for 6 months or longer * Less than 10 pack-years smoking history Exclusion Criteria: * Pulmonary function * FEV1 less than 50% predicted pre-bronchodilator * Other major chronic illnesses * Conditions which in the judgment of the study physician would interfere with participation in the study, e.g., non-skin cancer, endocrine disease, coronary artery disease, severe hypertension, immunodeficiency states * History of thyroid disease, breast cancer, ovarian, or endometrial cancer * History of physician diagnosis of chronic bronchitis, emphysema, or COPD * Medication use * Current consumption of soy isoflavone supplements * Oral corticosteroid use within the past 6 weeks * Use of tamoxifen * Use of an investigational treatment in the previous 30 days * "Drug" allergy * Known adverse reaction to genistein, other phytoestrogens, or soy products * Females of childbearing potential * Pregnant or lactating. Participants must agree to use effective contraception during the trial. * Non-adherence * Inability or unwillingness to provide consent or, in the case of children, inability or unwillingness of the child to provide assent * Inability to swallow study medication * Inability to perform baseline measurements * Completion of less than 10 of the last 14 days diary entries during screening period * Inability to be contacted by telephone * Intention to move out of the area within 6 months * Other * Recent asthma exacerbation (within 6 weeks) * Recent upper respiratory infection (within 2 weeks) * Body weight less than 77 pounds (35 kg) * Intake of soy or soy-enriched foods 1 or more times a week * Change in diet over the past month or expected change in diet during the study