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The genistein and daidzein in soy can also inhibit thyroid hormone synthesis. High soybean diets have been implicated in diet-induced goiter. This problem is not likely to occur in an average amount of soy in a varied diet. In some susceptible individuals, or in some who take very high doses of nutritional supplementation of soy isoflavones (above 200 mg per day), it is prudent to be aware of this potential interaction.