Q. Can too much soy cause thyroid problems? I drink a quart of soy milk and consume edamame every day, and have been diagnosed with an underactive thyroid. Could there be a connection?
A. Jenna Stefin, a dietetic intern at Tufts’ Frances Stern Nutrition Center, responds: “According to the most recent research, the interaction between soy products and the thyroid is dependent on whether an individual already has depleted iodine stores. One review found little evidence of a negative thyroid effect on healthy adults with adequate iodine stores who consumed soy. It seems that an iodine deficiency is needed before soy can have an adverse effect on the thyroid. Because of the increasing iodine deficiency among older Americans, however, postmenopausal women who consume high amounts of soy products may be at an increased risk of thyroid problems. The American Thyroid Association recommends that people who have been diagnosed with hypothyroidism (underactive thyroid) should take care to wait four hours after taking their thyroid hormone replacement before consuming any soy products.”