Should you avoid soy? Does it have a negative effect on the hormonal balance? Or quite the opposite? Is fermented soy better than unfermented soy? Do you contribute to the destruction of tropical rainforests by eating soy? And what about GMO and soy? Welcome to part 2 of a serial about… yes, of course: soy.

Our dear intern Sebastian, who studies to become a diet and nutrition advisor, did it again – he asked clever questions about soy to the nutritionist Anki Sundin. And, just as last time, the conversation below revolves around the soybean and other soybean products, such as soy sauce, tofu and soy milk.

– Can soy interfere with the hormonal balance in pregnant women?

– No, absolutely not. If consumed moderately, by healthy women with normal thyroid function.

– There’s phytic acid in soy. From my understanding, phytic acid inhibits the absorption of minerals in our intestine. Is that something to be concerned about?

– If you don’t have iron deficiency, or other mineral deficiency, you have nothing to worry about. Phytic acid will not completely inhibit the absorption, only partially. But if you know that you have some kind of mineral deficiency, I’d encourage you to learn more about food composition. In that case, you should perhaps think twice before combining iron-rich foods, like a bean stew, with foods high in phytic acid, since you need to help the body to absorb as much iron as possible.

– Does phytic acid act as an antioxidant?

– Yes.

– Do soy foods negatively affect the thyroid gland?

– As matters stand, if you have normal thyroid levels, I wouldn’t say so. But for people who suffer from some kind of thyroid disease, it may be a good idea to limit the intake of soy. That’s because soy protein interacts with the drug Levaxin, often used as treatment for reduced thyroid function. So, in some cases, you may want to avoid adding too much soy to your diet. But, I must emphasize, if you have normal thyroid levels, there’s absolutely no need to worry.

– Is it true that a large intake of soy may increase the need for iodine? I’ve read that soy isoflavones (a type of phytoestrogen) take up some of the the iodine that the body would normally use for thyroid hormone production (which regulates your metabolism).

– Yes, that’s a candidate mechanism. But what really happens when soy protein interacts with the drug Levaxin, is that soy inhibits the absorption of Levaxin in the intestine.

– But should I increase the intake of iodine if I eat a lot of soy?

– According to general dietary guidelines, you don’t have to. And as matters stand, I don’t believe normal or moderate consumption of soy would increase the need for iodine to the extent that we should be worried about it. But a candidate mechanism for the interaction of soy with iodine is that the phytoestrogens in soy bind the iodine and limit its availability. Iodine is essential to the production of thyroid hormones, which leads to the question: is it necessary for someone who eats a lot of soy, to also increase the intake of iodine? However, if that is the case, how much soy we’re actually talking about, and how much extra iodine, is still very uncertain.

– From our conversation, I understand you’re not opposed to people eating soy foods, as long as it’s in moderate amounts. Is that right?

– Yes. I’m definitely not opposed to people eating soy. But, from an ethical and environmental perspective, I do question the massive amounts of soy grown solely to feed animals.

Thank you once again, Sebastian. Can’t wait to hear more about this. Stay tuned.

Here’s part 1:

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