Daily Nutrition & Health
Understanding Phytoestrogens, Myths and Benefits of Soy Products
Susan Bowerman, M.S., R.D., CSSD, CSOWM, FAND – Sr. Director, Worldwide Nutrition Education and Training 1 August 2023
Maybe you’ve heard some things about soy, soy milk and soy products that got you thinking. Is it safe? Many people are unnecessarily concerned about natural phytoestrogens in soy. What exactly are phytoestrogens, and what are their effects on the body?
As a dietitian, I often recommend healthy proteins like soybeans and tofu in many of my recipes and meal plans. But people sometimes protest because they’ve heard bad things about soy. Although the pros and cons of soy have been studied rigorously in the past few decades, many myths and misconceptions still exist.
Benefits of Soy: Is It Actually Good for You?
Soy foods have long been recognized as good sources of protein, and in some parts of the world, soy has been part of our diets for thousands of years. In fact, there is a growing body of research to support the many health benefits of soy, and yet there is still some confusion.
Soybeans are not much of a dietary staple in the western world. But traditional soy foods, like soy milk, tofu, miso and tempeh, have formed the basis of diets in East Asia for centuries, where they’re valued not only for their versatility but also for the healthy nutrition they offer.
Soy has an impressive nutritional profile.
While all beans provide protein, soybeans top the list when it comes to protein quality. As a complete plant protein, soy contains all the essential amino acid building blocks that are used to manufacture all kinds of specialized protein structures our body needs.
Soy is also low in saturated fat and naturally cholesterol-free since only animals and animal products contain cholesterol. That, coupled with the fact that most of the fats in soy are polyunsaturated, makes soy a heart-healthy food.
Adding soy foods to your diet could boost your intake of vitamins, such as folate and vitamin K, as well as minerals like calcium, magnesium and iron. Also, you’ll increase your intake of fiber if you were to eat whole soybeans – and you can’t get fiber from animal proteins.
Soy protein supports muscle building.
When people think of muscle-building protein, they usually think of whey protein. Soy protein is actually effective for promoting muscle growth, too, but the stigma against consuming soy and its naturally occurring isoflavones – phytoestrogens (or “plant estrogens”) – has led some consumers to avoid it. They believe that these plant compounds may lower testosterone levels and interfere with muscle development.
This myth is false. According to a meta-analysis of studies related to soy protein and isoflavones, it was concluded that neither soy foods nor isoflavone supplements had any significant effects on testosterone concentrations in men.
Soy is a great source of protein and is also rich in arginine, the amino acid that the body uses to produce nitric oxide. Nitric oxide increases blood flow to the muscles, which helps deliver nutrients and oxygen during your workouts.
Soy is a sustainable alternative to animal proteins.
You can help the planet by consuming more plant-based protein like soy. When compared to the environmental impact of raising farm animals, soy production uses less water and land and produces less greenhouse gases, too.
Despite these benefits, some people still hesitate to trust soy foods, often citing a rumor or an outdated study. Let’s take a science-based approach to these common questions and claims.
Myths and Concerns Around Soy: Are Phytoestrogens Bad?
Plant estrogens are not the same as natural estrogen produced by the body. Understanding the difference is key.
The misunderstanding seems to stem from the fact that soy (and plenty of other foods, by the way), contains natural plant compounds called isoflavones, which are classified as “phytoestrogens” (“phyto” means “plant”).
So when people hear that soy foods contain “phytoestrogens,” they may turn their backs on soy foods in fear that they will expose the body to “too much estrogen.” Not true.
Let me explain the difference as clearly as I can:
Isoflavones are referred to as phytoestrogens or “dietary estrogens” because they have a chemical structure that’s similar – but not identical – to natural estrogen, the hormone produced by your body’s endocrine system.
Phytoestrogens are part of a plant’s natural defense system, working primarily to protect the plant from damaging fungus – which is why you’ll find them in many foods.
Although soybeans are probably their richest source, phytoestrogens can be found in all kinds of beans, nuts, whole grains and seeds like flax and sesame. There are even small amounts in certain fruits and vegetables, including apples, carrots and yams.
The key point is this: phytoestrogens in soy are not the same as estrogen made by the body and do not exert the same effects on the body.
How do phytoestrogens work in the body?
Explaining how this works may help you understand why the natural compounds in soy have been so misunderstood:
Certain tissues of the body, such as the breast, bone and prostate, have structures within their cells called estrogen receptors (E.R.). These receptors sit inactive inside the tissue cells until estrogen enters the cell. Once estrogen gets inside and binds to the receptor, the estrogen can then exert its effects inside the cell.
Here’s where things get a bit more complicated – but stay with me. There are actually two different types of estrogen receptors, and the body’s natural estrogen isn’t particularly picky about which one it will bind to – it will happily bind to both types of receptors.
On the other hand, phytoestrogens – like the isoflavones in soy – prefer to connect with only one type of receptor. And this is what makes phytoestrogens so distinctly different from the body’s own estrogen.
Since phytoestrogens prefer to bind with one type of receptor over another, it means two things. First, it means that at those receptors where phytoestrogens don’t mind binding, natural estrogen can attach itself and exert its effects within the cell. But when phytoestrogens bind to their preferred type of receptor, they sort of “get in the way” – which makes it more difficult for the body’s natural estrogen to bind.
And herein lies the unique effects of phytoestrogens: they can act like estrogen in some tissues, while in others, they can interfere with the action of the body’s natural estrogen. So these plant compounds may mimic the effects of estrogen in tissues where it may be beneficial – and at the same time, they may interfere with the action of estrogen in other tissues where reduced exposure to estrogen might be considered protective.
The bottom line is this: the effects of isoflavones in the human body have been studied extensively, and as a recent review article noted, “There has been no indication of risk to human health because of consuming soy or soy isoflavones as a regular part of the diet … on the contrary, studies over the last decades have suggested protective effects of these compounds.”
Does soy increase breast cancer risk?
Soy isoflavones do not increase breast cancer risk. This confusion about phytoestrogens has led some women to shun soy foods in the mistaken belief that these plant estrogens will increase their body’s exposure to estrogen and increase their risk for breast cancer. It turns out, however, that the opposite may be true.
Can soy actually reduce breast cancer risk?
In the case of breast cancer, concerns about soy increasing natural estrogen levels are unfounded. In fact, the incidence of breast cancer is lower in countries where soy is consumed regularly.
In Asian epidemiologic studies, a higher consumption of soy in early life is associated with a 25 to 60 percent reduction in breast cancer risk. Similarly, the North American Menopause Society has concluded that soy-based isoflavones do not increase the risk of breast or endometrial cancer.
Does soy have feminizing effects on men?
Colloquially known as “man boobs,” this myth has caused some men to avoid soy products completely. While it certainly makes headlines, this has been reported in only one study, which documented the “feminizing” effects in a 60-year-old man who drank three quarts of soy milk daily.
It was estimated that the subject was taking in 360 milligrams a day of isoflavones – nine times the amount of isoflavones typically consumed by older Japanese men, among whom soy intakes are already higher than the worldwide average. The subject’s high soy intake was also in the context of an unbalanced and nutrient-deficient diet since most of his calorie consumption came from soy foods.
One should not draw conclusions from one case, and in numerous clinical trials, there has been no report of feminizing effects in men who were exposed to as much as 150 milligrams a day of soy isoflavones.
How to Incorporate More Soy Into Your Diet
Soy is actually very versatile, and there are many convenient and practical methods to enjoy soy every day. Here are a few examples:
Edamame are fresh green soybeans. You can often find these in your grocer’s freezer, either in the pod or already shelled. After briefly cooking them in salted water, they can be eaten as a snack or added to soups and salads.
Tempeh is made from soybeans that are partially cooked, allowed to ferment and then formed into a firm block. Since tempeh is fermented, it’s a source of “good bacteria,” or probiotics. It has a meaty flavor and firm texture that holds its shape, so it’s great for salads and stir-fry dishes.
Miso is a paste made from fermented soybeans, which means it also contains probiotics. It’s used as base for soup as well as an ingredient in sauces, salad dressings and marinades. There are different varieties, and the color can range from light yellow to very deep brown. In general, light miso is less salty and milder in flavor than dark miso.
Soy milk is made from dried soybeans which are soaked in water until they’re rehydrated and then ground with water. The resulting milk is sold as a beverage or made into yogurt. Soy milk and soy yogurt each have about 7 grams of protein per 8-ounce (250 milliliters) serving. You can use soy milk as a beverage on its own, or you can substitute it for regular milk in most recipes or in protein shakes.
Soy nuts are roasted whole soybeans. They make a nice snack on their own, and they’re also good in salads, trail mix and on cereal. Soy nuts (and soy nut butter, which is made from ground soy nuts) have a bit more protein and a bit less fat than peanuts or peanut butter.
Soy protein powders and meat substitutes are made from soybean flour that’s had most of the fat removed. The powders can be added to shakes or stirred into oatmeal, and the soy meat substitutes can be used in all sorts of recipes in place of meat or poultry.
Tofu is essentially a cheese that’s made from soy milk. It ranges in texture from extra firm to extra soft and has a very mild flavor. It mixes well with anything from spicy sauces to naturally sweet fruits. The firmer type of tofu is good for grilling or stir-frying, while the softer, creamier style is good in shakes or sweetened and topped with fruit as a dessert.