Should I Be Eating Soy?
Get the pros and cons of eating soy. (Photo: John Block/Blend Images/Getty Image)
It happens again and again. There’s a food that the public eats — one that mankind has consumed for a very long time. Someone publishes research that associates that food with a negative health effect. The experts tell everyone to avoid that food, and everyone freaks out. Eggs are tossed into the harbor. Fat is burned in effigy. Shakers of salt are smashed in public squares.
Now soy is having its panic-in-the-streets moment. Is soy a monster bent on destroying mankind? Is it a misunderstood ally of the human race? Let’s try to get to the bottom of the bean.
Doesn’t Soy Contain Phytoestrogens?
One of the knocks against soy is that it contains phytoestrogens, a group of natural compounds that resemble estrogen organically. According to Heather B. Patisaul of North Carolina State University and Wendy Jefferson of the National Institute of Environmental Health Sciences, whose review “The Pros and Cons of Phytoestrogen” was published in Frontiers in Neuroendocrinology, the jury is still out on phytoestrogens. Patisaul and Jefferson wrote: “A litany of health benefits including a lowered risk of osteoporosis, heart disease, breast cancer and menopausal symptoms are frequently attributed to phytoestrogens, but many are also considered endocrine disruptors, indicating that they have the potential to cause adverse health effects as well.
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Consequently, the question of whether or not phytoestrogens are beneficial or harmful to human health remains unresolved.” (Endocrine disruptors are chemicals that may interfere with the body’s endocrine system and produce adverse effects.) The researchers say soy’s effects are most likely complex and could depend on the age, health status and even the presence or absence of specific gut microflora in the individual.
The most damning research on endocrine disruption comes from studying animals, and it’s a body of work many have called into question. For example, some studies use only newborn mice, and instead of eating phytoestrogens, the mice are injected with them, bypassing normal metabolic pathways.
So what’s a phytoestrogen-wary individual to do?
“It’s all things in moderation,” said Patisaul, an associate professor at North Carolina State. “When I talk about soy in class, I talk about it like beer. If you’re an adult and you go out and have one or two beers, you can expect not to have any serious adverse health outcomes. If you drink 10, then you’re going to have a problem. It sort of depends on your life stage and how much you’re consuming and what other types of health issues you have.”
Can Soy Affect Thyroid Function?
The thyroid is an endocrine gland that makes hormones, which control the rate of many metabolic activities in the body. A 2006 review of 14 trials by researchers from Loma Linda University published in the journal Thyroid looked at the effects of soy food on at least one measure of thyroid function in healthy humans.
The review revealed that soy and its isoflavones, a class of phytoestrogens, present little evidence of adversely affecting thyroid function. The study was written by Mark Messina, who, in addition to being a Loma Linda University professor and internationally recognized expert on the health effects of soy, is also a consultant for companies that manufacture and/or sell soy food.
Is Soy Connected With Breast Cancer?
Soy is not a known cause of breast cancer. In fact, the American Cancer Society calls soy “an excellent source of protein and a good alternative to meat.” But estrogen plays a major role in breast cancer, which is why researchers are interested in revealing how soy and its phytoestrogens affect breast cancer survivors.
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A 2001 study published in the Annals of Pharmacotherapy found that low concentrations of genistein and daidzein, the major phytoestrogens in soy, stimulated breast tumor growth in animals. Genistein and daidzein also antagonized the antitumor effect of the breast cancer drug tamoxifen in the lab. The researchers concluded: “Genistein and daidzein may stimulate existing breast tumor growth and antagonize the effects of tamoxifen. Women with current or past breast cancer should be aware of the risks of potential tumor growth when taking soy products.”
University of Southern California researchers, funded by the California Breast Cancer Research Program and by a grant from the National Cancer Institute, found that observational studies showed a decreased risk of breast cancer development in association with high intake of soy. Clinical and intervention studies on the short-term effects of soy products, however, have not shown clear beneficial or harmful effects.
The American Cancer Society says: “There is growing evidence that eating traditional soy foods such as tofu may lower the risk of cancers of the breast, prostate, or endometrium, and there is some evidence it may lower the risk of certain other cancers. Whether this applies to foods that contain soy protein isolates or textured vegetable protein derived from soy is not known. There is little data to support the use of supplements of isolated soy phytochemicals for reducing cancer risk.”
If there is a firm link between soy and lowering the risk of breast cancer development, it has yet to be established.
Soy Allergies
Soy induces an allergic reaction in a small portion of the population. Some babies, for example, are allergic to soy-based formula. Most children lose their allergy as they age, but soy allergies also can spring up during adulthood. There is good news for soy eaters with soy allergies: Fermented soy may cause drastically fewer allergic reactions. In 2008, University of Illinois researchers revealed that fermented soy reduces potential allergenicity and increases essential amino acids.
The Trouble With Highly Processed Soy, a.k.a. Soy Protein Isolate
Sales of soy foods in the United States crossed the $5.2 billion mark in 2011. Today, processed soy protein (in the form of soy protein isolate) is used in protein bars, breakfast cereals, salad dressings, soups, cheeses, nondairy creamers, whipped toppings and infant formulas.
Some doctors and nutritionists — among them Dr. Caldwell Esselstyn Jr. of the Cleveland Clinic; Dr. Dean Ornish, Dr. Andrew Weil and Dr. Mark Hyman; and Ashley Koff, a registered dietitian and co-author of “Mom Energy: A Simple Plan To Live Fully Charged” — recommend avoiding foods containing soy protein isolate, including fake meats, soy cheeses and protein bars. Weil, Hyman and Koff have spoken out to say that these highly processed soy products do not have the health benefits of whole natural soy. Koff has expressed concern that soy protein isolate may disrupt hormones.
So, Are There Any Benefits to Eating Soy?
Soy is a complete plant protein that contains all the essential amino acids. Whole soy (such as steamed edamame beans) and fermented soy (in the form of miso, tempeh and some types of tofu) have long been staples of Asian diets. Populations that consume whole and fermented soy, such as those in East Asia, have been proven to have less breast cancer, prostate cancer and cardiovascular disease, as well as fewer bone fractures. Women report fewer menopausal symptoms, and both sexes have a lower incidence of age-related brain diseases. Interestingly, when Asians immigrate to Western nations, including the United States, and adopt the native cuisine, their disease rates change.
If you decide to consume soy after weighing the pros and cons, for the full benefits choose whole soy (such as steamed edamame) or fermented soy (such as miso or tempeh), and minimize your intake of highly processed soy contained in many packaged energy bars, shakes and foods like fake meats, soy cheeses and soy ice creams. Be sure to check the labels.
To read more of Joe Donatelli’s breakdown of soy and whether you should be eating it, click here.
By Joe Donatelli
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