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Vegan Nutrition with Dina Aronson, M.S. R.D.Dina Aronson, MS, RD is a vegan dietitian whose specialties include chronic disease prevention, vegetarian/vegan nutrition, and lifestyle management. She is the founder and director of VeganRD.com, a nutrition consulting company. Active in many vegetarian nutrition organizations, Dina was the recipient of the American Dietetic Association's Recognized Young Dietitian of the Year Award in 2002.
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I have been vegan for three years and have always suffered with weight problems. I was recently diagnosed with hypothyroidism. It has been suggested to me that an over consumption of soy products may have contributed to depleted thyroid function. Is this true? If I were to avoid soy products, what should I do to ensure proper nutritional balance in my life? I definitely do not want to start up with dairy again, something I have been harassed about doing lately...
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Indeed there is a lot of information-and misinformation-out there about the relationship between soy and thyroid disease. I hope to set the record straight.
First, a little background. The most common cause of hypothyroidism is an autoimmune condition (Hashimoto's Thyroiditis). This condition is thought to be genetic, not caused by lifestyle or diet. Hypothyroidism can also be caused by iodine deficiency, but this is rare (but not unheard of) in the US since iodine is added to salt, bread, and other foods, and is found naturally in sea vegetables (more about iodine below).
The basis for the premise that soy will interfere with thyroid hormones is that isoflavones, healthy constituents of soy, are similar in structure to thyroid hormones. Also, it has been observed that when soybeans are fed to iodine-deficient rats, the rats developed goiter and hypothyroidism (correcting the iodine deficiency prevents these conditions).
A healthy person who consumes several servings of soy products per day is not at an increased risk for thyroid disease, unless the diet does not contain enough iodine. So for healthy vegans consuming a balanced diet, too much soy will not contribute to compromised thyroid function.
For people who have a thyroid disorder, and/or are taking medication for one, some research has suggested a relationship between soy and thyroid function. Fortunately, Mark Messina, soy expert, recently co-authored a review article that evaluated several studies on this subject and concluded: "…collectively the findings provide little evidence that in euthyroid [having a normal thyroid gland], iodine-replete [no iodine deficiency] individuals, soy foods, or isoflavones adversely affect thyroid function. In contrast, some evidence suggests that soy foods, by inhibiting absorption, may increase the dose of thyroid hormone required by hypothyroid patients. However, hypothyroid adults need not avoid soy foods." (Thyroid. 2006 Mar;16(3):249-58.) Thus, it is possible that in people with a pre-existing hypothyroid condition, their soy intake may affect the dose of medication needed. Those individuals need to consult their doctor, who will make recommendations on medication dose based on blood tests and other observations.
Any concerns about the effect of soy on thyroid function can be addressed by having blood thyroid hormone levels measured. This is a typical test anyway, since the American Thyroid Association recommends that all people have their thyroid hormone levels checked every five years beginning at the age of 35. And for many, thyroid tests are routinely ordered as part of a regular medical checkup.
Again, the risk of thyroid problems increases if we don't consume enough iodine. How do we know if we're getting enough? Iodine is an essential mineral, and it's one that we don't hear much about. Most people get iodine from fish, and lacto-vegetarians get iodine from dairy (since milk machines are cleaned with an iodine solution). Vegans at greatest risk for iodine deficiency are those who consume no added salt and no packaged foods.
For those vegans who think they might not be getting enough iodine, it is wise to use iodized salt in cooking. And even tiny amounts of sea vegetables (such as dulse, nori, etc.) supply ample amounts of iodine. Vegetables grown in iodine-rich soil are good sources, but so much of our topsoil is nutrient-depleted that we can't depend on them. (Before widespread use of modern agricultural methods, soil was naturally rich in iodine, and people got enough iodine from the food they grew and bought at market.)
If you decide to avoid soy (as many do for other reasons, such as a soy allergy), it can be done. The nutrient most vegans are concerned about when giving up soy is protein. It is certainly possible to meet protein needs on a soy-free, vegan diet. Most vegetables, nuts, seeds, and beans are excellent protein sources. See this question/answer for more about meeting protein needs on a soy free diet. If you were getting most of your calcium, vitamin D, and vitamin B12 from fortified soy milk, it is important to find other reliable sources of these nutrients. Fortified rice milk, fortified nut milks, supplements, and many cereals contain added nutrients that will help meet your needs.