I was a hippie in college and very proud of my vegetarian diet. I started shunning animal products at age 15, and after living on rice and ramen for a while (which left me severely anemic), I decided to get “healthy” and include whole grains, legumes, and plenty of soy protein and soy milk. I felt pretty great for a long time until I began to notice nagging digestive issues like bloating, and I lost my period for over a year.

Fortunately I began studying nutrition and hormonal health around that time, and I learned that soy has the potential to adversely affect thyroid and female hormone health. I stopped eating and drinking it immediately, and slowly my hormones rebalanced themselves, and my period returned (I also added in specific herbs such as vitex to help boost progesterone). Sadly, however, my thyroid function suffered, a common side effect of too much soy, and I am now hypothyroid (which does run in my family).

I’ve written about the dangers of over consuming soy both here and here , but this isn’t going to be another article telling you soy is the root of all evil and no one should ever touch the stuff. There are guidelines about how and why to safely consume soy foods, who can safely consume soy, and the types of soy that are ok to eat.

Just How Bad is Soy?

Remember when the soy craze hit back in the late ’90s? Soy prevents heart disease! Lowers cholesterol! Relieves menopausal symptoms! Many of these claims even began to show up on packaged foods, encouraging us to eat soy, because if a little is good, more must be better, right?

Actually, no.

Currently the FDA is even proposing a rule to revoke a health claim for soy protein and heart disease. (source)

Soy is everywhere in our food supply, and most Americans are consuming over 25 grams of it per day (for perspective, Asian cultures consume 7 or less grams of unprocessed or fermented soy). Soy is cheap, a government subsidized crop, and is processed into everything from oil to flour to nuts to lecithin, the emulsifying agent you’ll find in almost all of your chocolate. Oh, and protein powders, protein bars, fake meat products. And don’t forget about soy milk, a very concentrated form of plant-based estrogens. Yep, soy is ubiquitous and you’re consuming much more of it than you think.

Most of the soy in our food supply is highly processed into soy protein isolates, hydrolyzed soy protein, textured soy protein, and of course the refined oil, flour, and other packaged food products. Not to mention the soy that’s in the feed the animals you’re eating are fed: don’t forget that you are what you eat ate! Back in my vegetarian days, I’d have a soy milk smoothie for breakfast, soy nuts or edamame for a snack (or a protein bar that contained soy protein isolate), a veggie burger for lunch, and tofu with veggies for dinner. I thought I was eating super healthy, but little did I know that I was exposing myself to the equivalent of over 2 birth control pills’ worth of estrogen daily.

Soy is high in plant-based estrogens, or isoflavones. Consuming too much soy contributes to estrogen dominance, a hormone imbalance that is the precursor to hormonal cancers. Many other foods, such as flaxseeds and lentils, contain isoflavones, but we’re not consuming flax milk, isolated flax protein, and flax burgers daily, are we? My point is the amount of soy we consume–in addition to the forms in which we consume it–are the problems.

Here’s the confusing part, though. In some people, consuming phytoestrogens like flax may actually reduce the estrogen load in the body, while in others, it raises estrogen. (source) This means that phytoestrogens can be estrogenic or antiestrogenic and can, therefore, have either a protective or causative effect on the development of cancer and chronic diseases. It’s impossible to tell without testing and monitoring which camp you’re in.

Soy is very difficult to digest, so traditionally, whole soy has been fermented into miso or natto. The fermentation produces probiotics and enzymes and makes it easier to digest. I used to get bloated after eating edamame and tofu. That’s one indication you’re not digesting it well. It could also indicate a soy intolerance. Soy, gluten, and dairy are among the 3 most allergenic foods.

How to Consume Soy Safely

If you do not have a soy allergy/intolerance (click here to learn how to do an elimination diet to determine your food intolerances), you can include small amounts of the fermented forms safely. Miso, tempeh and natto are all fermented and are ok. Use caution with tofu and edamame. Though they are minimally processed, tofu and edamame are difficult to digest and contain anti-nutrients that block absorption of other nutrients (fermenting reduces the anti-nutrients).

AVOID: soy milk, soy protein, soy oil, and other forms of processed soy such as soy protein isolates. Soy milk has a high level of plant-based estrogens (isoflavones) and usually has sugar added. Soy oil is highly refined and oxidized, making it inflammatory. Processed soy overall contains concentrated amounts of isoflavones.

BOTTOM LINE: soy doesn’t work for everyone. Processed soy foods can be very detrimental. Whole, unfermented soy is very difficult to digest. Because the food industry spins soy as a health food (these days are coming to an end it seems), many people make soy products the base of their diets (soy protein, soy milk, soy snacks, tofu, etc), and in such doses it can absolutely cause problems. If soy is right for you, choose the fermented forms.

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Mary Vance (Certified Nutrition Consultant)

Mary Vance is a Certified Nutrition Consultant and author specializing in digestive health. She combines a science-based approach with natural therapies to rebalance the body. In addition to her 1:1 coaching, she offers courses to help you heal your gut and improve your health. Mary lives in San Francisco and Lake Tahoe in Northern California. Read more about her coaching practice here and her background here.