The Skinny On Soy

Back in 2002 when the Women’s Health Initiative concluded that supplemental estrogen led to higher rates of breast cancer, blood clots and cardiovascular disease, the medical community resurfaced in a panic. Prior to this landmark study, estrogenic hormone replacement had only ever been touted for its positive side effects, such as improving bone health and reducing menopausal symptoms. Drug companies everywhere set out to design a physician’s ideal prescription – a selective estrogen receptor modulator.

In simpler terms, the industry needed a product that could offer consumers the best of both worlds. A drug that could provide pro-estrogenic effects in tissues like bone (where estrogen proved beneficial), but anti-estrogenic effects in others like breast tissue (where higher estrogen levels were associated with increased cancer risk). But how could a single hormone behave so differently in two regions of the body?

The answer lies in that there are two types of estrogen receptors within our anatomy: alpha and beta. And how a certain tissue or organ responds to estrogen has to do with which type of these (alpha or beta) receptors it has.

So where does soy fit into to all of this? Where does a simple legume find its place in the middle of a narrative polluted with rumors of thyroid disease, cancer and man-boobs (among other eminence)?!

It all started with the discovery of a certain class of phytochemicals (or “plant” chemicals) called isoflavones. Soy foods such as soy beans, edamame (soy beans harvested at 80% ripeness), miso, tofu, and tempeh are rich in these isoflavones - a molecule that vaguely resembles our own estrogen on a molecular level.

There's one problem. The media LOVES to end the narrative right there.

“If soy has these estrogen-like compounds, it must lead to things like breast cancer and male feminization, right?!”

In reality, the phytoestrogens from foods like soy behave entirely distinct from our own endogenous estrogen. Unlike the estrogen we produce, soy estrogens (or isoflavones) preferentially bind to beta estrogen receptors.

It’s for this reason that tissues predominantly containing alpha receptors, such as the liver, uterus, prostate and breast are not negatively impacted by soy consumption. In fact, the plant-estrogens in soy can sit in these estrogen receptors (as if to “save a seat”), preventing our own estrogen from binding to those receptors and exerting much stronger estrogenic effects. This leads to a cascade of benefits that ultimately prevents the liver from pumping out too many blot clotting factors, promotes the improvement of menopausal symptoms, and significantly reduces the risk for endometrial, breast, prostate and gynecological cancers.

The consumption of soy has been shown to not only reduce the risk of breast cancer but also improve breast cancer survival, reduce recurrence rates and extend longevity.

In fact, women who consume soy foods (ideally starting in adolescence) have between 30-50% reduced risk of breast cancer, and the countries that consume the most soy like Japan have some of the lowest breast cancer occurrence rates worldwide.

Additionally, studies like this one have found that consumption of just one serving of soy milk per day results in a whopping 70% reduction in the risk of prostate cancer, thanks to the tumor-suppressing effects of beta cells located on the prostate gland.

With regards to skeletal health, human bone cells contain beta estrogen receptors. This explains the breadth of research associating soy phytoestrogen consumption with reduced bone loss, enhanced bone mass formation, and a significantly reduced risk of bone fractures with just a single serving (5-7 grams of soy protein) consumed per day.

Soy has also been shown to lower cholesterol and aid in the prevention and reversal of clogged arteries, helping prevent the number one killer of men and women in our nation (heart disease), as well as reverse related conditions such as erectile dysfunction.

The bottom line: Soy is perfectly safe and actually protective for men and women alike.

However, keep in mind here - variety is the spice of life! You would never eat six servings of “kidney-bean protein isolate” in one day, and the same should go for any other bean or legume (such as soy). Variety in our protein sources is critical for a diverse microbiome as well as to ensure we ingest plenty of different amino acids, phytochemicals and disease-fighting compounds daily.

Consume this healthy legume in moderation like any other source of protein (<3 servings per day), ideally in organic, minimally processed forms.

And fermented with live and active cultures like tempeh or miso? Now we’re in BONUS POINTS territory, friends.

Fermentation makes soy more digestible and adds flavor. It also deactivates soy’s natural phytic acid and enzyme inhibitors, which can affect protein absorption and negatively impact the bioavailability of minerals like iron, zinc and calcium.

Note: Tempeh, miso, tamari and shoyu are fermented. Tofu is not fermented, but tofu does not negatively affect mineral or protein absorption because of the way that it’s made.

More highly processed soy foods such as burgers and products with isolated soy protein or soy flour are best left as occasional treats. When a food is made from "soy protein isolate”, that’s typically a sign that it’s more heavily processed and could contain additives, fillers, excessive amounts of salt, sugar or other appetite-enhancing compounds. Some highly processed forms of soy include textured vegetable protein, protein powders, and soy flour-based meat analogs.

Finally, let’s address the elephant in the room here. Beer lovers, focus up.

Hops actually have higher levels and more potent phytoestrogens than soy. So if you’re really worried about phytoestrogen consumption, you might consider a hard pass on the pale ale next time before you go on demonizing edamame.

And don't get me started on dairy.

If we're going to take the time to dissect the consumption of dietary estrogens we need to consider the levels of mammalian estrogen present in the breastmilk of a pregnant cow. Not to mention the fact that the majority of the genetically-modified soy produced in the world is fed to livestock in order to fatten them up for slaughter. Meanwhile, we humans have easy access to the organic, non-GMO stuff in stores.

Additionally many restaurants and fast food chains mix their beef with soy protein to cut costs and add moisture - and that’s about as processed and genetically modified as soy comes, to be frank. So if soy is the enemy in your mind, I might suggest dropping the late night Jack In The Crack like the bad habit that it is.

With all of that behind us, let’s decode some common sources of soy, taking note of some of my favorite, minimally processed forms, starred (*) among the rest.

*Edamame are raw green soybeans, harvested at 80% ripeness when the beans are still young and sweet. As a whole food, they’re high in fiber and the protein is naturally intact. Edamame are sold fresh in the pod as well as frozen, shelled or unshelled.

Soybeans are hard, dry beans that have ripened in the pod. To prepare, soak in plenty of water overnight in the refrigerator, then cook for three to four hours to use in stews and soups. Cook thoroughly to ease digestion.

Soynuts are whole soybeans that have been soaked in water, lightly oiled and baked until brown. They’re a convenient, crunchy snack food and maintain intact the high protein and isoflavones valued in soy foods.

Soynut butter is made from roasted whole soynuts that are ground and sometimes blended with soybean oil. Soynut butter contains significantly less fat than peanut butter.

*Miso is a rich, salty paste made from a fermented mixture of soybeans and a grain, such as barley or rice. Use it as a base for broth, soup or condiments such as dips, dressings and sauces.

Convenience soy foods are designed as alternatives for many meat, chicken or dairy products. They include soy dogs, soy burgers, soy jerky and soy cheeses. While high in protein, they’re based on isolated soy protein (soy protein isolate) and should be eaten sparingly as treats as opposed to regularly-consumed staples.

Soy flours are gluten-free and may substitute in small amounts for other flours in recipes to tenderize baked goods. Sensitive to light and heat, soy flour should not be used to dredge foods for sautéing. Refrigerate or freeze in tight glass containers.

Soy milk, also labeled as soy beverage, is made by cooking the creamy milk of crushed soybeans. Most brands add sweeteners, nutrients or plant-based thickening agents to give soy milk a consistency similar to cow’s milk.

Soy yogurt, cream cheese, sour cream and frozen desserts are all based on soy milk as the basic ingredient.

Soy cheese is made from soy milk and sometimes isolated soy proteins. Unless specifically labeled as non-dairy or vegan, soy cheese typically contains cow’s milk protein called casein or caseinate.

Soy infant formula, made from a soy protein isolate base, is for infants not able to nurse or tolerate dairy-based formulas. Some professionals question the effects of infant consumption of isoflavones in this form.

Soybean oil has a neutral flavor, contains no cholesterol and though rather processed, is an easy way to add essential fatty acids into the diet.

*Soy sauce (tamari, shoyu) traditionally is the salty liquid by-product from making miso and is used for seasoning. Choose a “naturally brewed” product instead of chemically extracted, mass-market sauces flavored with corn syrup. Shoyu is made from a blend of soybeans and wheat. Tamari is a wheat-free variety.

*Tempeh is a fermented food made of whole soybeans or a mixture of soybeans, grains and seeds. It’s high in protein and fiber and is a good source of iron and zinc. Tempeh can be fried, baked, sautéed or barbecued, but should be cooked at least 10 to 15 minutes for optimal digestibility.

Textured soy protein (TSP) is a highly processed source of soy protein that appears in many packaged foods. In bulk form, it readily absorbs liquid and takes on the flavor of other ingredients in a recipe.

Textured vegetable protein (TVP®) is similar to textured soy protein. TVP is higher in protein and iron than TSP and rich in potassium, magnesium and phosphorus.

*Tofu is a soybean curd created by stirring a thickener into warm soy milk. It comes in soft/silken, firm or extra-firm varieties. Non-silken varieties can be an excellent source of calcium if the thickening agent contains calcium.

Some of the favorite ways to incorporate these minimally-processed forms of soy are teriyaki tempeh bowls, vegan miso ramen, turmeric tofu scramble, spicy thai peanut salad, creamy vegan chocolate mousse and even some good old-fashioned whole grain cereal with sliced bananas and soy milk.

If you enjoy this versatile protein as much as I do, rest assured you are safe to proceed with health benefits in mind!

Thanks so much for tuning in! I hope you walk away from this post feeling empowered, assured, and maybe even a little bit inspired to get creative in the kitchen.

Before you go, be sure to leave a comment over on my Youtube, Instagram, or TikTok to let me know what kind of content I can create to best serve your mind and body well this season and beyond.

Until next time!

Gracie

This post was written & medically reviewed by a Registered Dietitian Nutritionist.

Grace Pascale, MS, RDN. Grace Pascale Nutrition.