Dear confused in Minnesota,

In health advice, guidelines are usually targeted to the general public. They don't take into consideration all the needs of individuals within the population. This may be the case with soy foods.

Soy foods contain some very active compounds — isoflavones, which can greatly impact health in a variety of ways. They can help lower blood cholesterol levels, protect bones against osteoporosis, and relieve some symptoms of menopause.

Alice understands your confusion about soy and your thyroid, because the knowledge in this area does not seem to yield specific answers. So far, here is what we know: two isoflavones found in soy — genistein and daidzein — compete for an enzyme that is used to make thyroid hormone. Usually, the effects are only seen when a person is iodine deficient (iodine is needed for thyroid hormone, too). Soy isoflavones' impact on thyroid status has been studied for years. Animal studies have been inconsistent in proving soy intake influenced thyroid status. Studies on infants born with thyroid disease showed that increased levels of thyroid hormone replacement was necessary when fed soy formula, but the exact reason for this remains unclear. There are no studies to date measuring the effect of isoflavone intake on thyroid hormone status in adults with hypothyroidism.

Alice cannot recommend a safe level of soy intake for you, because the safe level is not firmly established. As a result, it's wise to proceed with caution. If you decide to try soy, be sure to wait at least three to four hours from the time you have taken your medication to eat the food. Your intake probably needs to be occasional — certainly not every day. Read food labels to detect sources of soy in processed foods — sometimes it is listed as "hydrolyzed vegetable protein." Do not take any supplements containing isoflavones, as these are very concentrated sources. If eating soy foods is what you choose to do, it's important for you also to have your thyroid status checked periodically by your health care provider and discuss your decision with him or her.

Alice

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