The issue of soy and isoflavone activity is in question today based on its potential effect on estrogen levels. Until more definitive research is available, 1 serving per day should be a safe level for anyone, including those who have a current or family history of estrogen-induced health issues (such as breast and ovarian cancer). If you are not at risk of these types of health issues and wish to use more soy products, 2 to 3 servings (some professionals suggest as many as 5) can be safely used. Soy foods can offer unique health benefits for most everyone when consumed daily in moderation.