October 5, 2011
Is soy causing your
fatigue and weight gain?
Health experts continue to debate the health benefits of soy. Some studies say soy is good for you. Other studies say soy can have negative effects on your health. I try to bring you both sides of the soy controversy, give you my own medical opinion, and let you decide whether to eat soy or not. Now there’s another study that warns about soy’s impact on your thyroid.
In this study, the researchers followed people with borderline thyroid function at the start of the study. The researchers gave the participants either a “low dose” of soy phytoestrogens (2 mg) or a high dose (16 mg) every day. The researchers chose these doses because the typical American diet has about 2 mg of phytoestrogens. But vegetarians consume up to 16 mg daily.
The study revealed that soy phytoestrogens can have a negative impact on the thyroid of some people. The researchers said soy can increase the risk of overt hypothyroidism in those who have a thyroid that’s borderline. In other words, the soy can push your thyroid into hypothyroidism, which can cause loss of energy, fatigue, and weight gain. But this study gets even more interesting.
The researchers found that the 16 mg dose reduced both systolic and diastolic blood pressure. But the 2 mg dose lowered only the systolic pressure. The higher dose improved insulin resistance and C-reactive protein levels as well. These are crucial markers of cardiovascular risk. The lipid profile remained unchanged. No one in the low dose group developed overt hypothyroidism, but 10% in the high dose group did.
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The study isn’t going to solve the soy controversy. It showed both good and bad effects. Only the bad effects carried a relatively small risk. There definitely are some people for whom soy products might cause problems. If you’re taking, or plan to take, larger amounts of soy isoflavone supplements, please get your thyroid level checked first. I don’t think that’s necessary for occasional soy product consumption – and this study confirms my recommendation here.
One question this study didn’t answer is why soy seems to be so good for Asian, but increases some risk factors in Americans. The researchers speculated that it could be related to iodine consumption. Asians tend to have a lot more iodine in their diet than Westerners. And iodine protects your thyroid.
I still believe soy has protective benefits for most people. Be cautious if you have any risk of a marginal thyroid. If you do, check your thyroid function regularly with your integrative doctor if you plan to take large amounts of soy or soy products.
“The Effect of Soy Phytoestrogen Supplementation on Thyroid Status and Cardiovascular Risk Markers in Patients with Subclinical Hypothyroidism: A Randomized, Double-Blind, Crossover Study,” J Clin Endocrinol Metab, 2011 Feb 16; [Epub ahead of print]. 48527 (05/2011).
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