Every so often, articles on the internet question the dangers of foods that we recognize as having health and nutritional value. In a recent post by a patient, soy milk safety was questioned because of certain statements made on a website. Since we always respect patient concerns and questions — recognizing our responsibility to stay on the cutting-edge of information — we therefore are addressing the several issues that were raised. And we would be happy to discuss and supply the substantial science supporting our response.
First, while we don’t recommend that patients consume multiple, large daily amounts of soy food, neither do we, based on solid science, regard it as a harmful menu item. As for soy milk, using a cup per day of a non-GMO brand that has no added sugar (sucrose) is not problematic even for breast cancer patients. Plus, fermented soy foods such as tempeh can make an excellent complete protein dish – and because of fermentation, it is one that is understood to be easier on digestion and with specific benefits due to the fermentation process. Tofu, another complete protein source, containing all the essential amino acids, is versatile and not harmful to health, even though technically a partial soy food, meaning absent of the fiber of the total soy bean. Again, moderation is always a key criterion in any food intake.
However, there are some people for whom soy might not be a good choice because of identified allergic reactions or other specific intolerances to soy. Also, people taking one type of antidepressants called monoamine oxidase inhibitors might be exposed to a drug interaction due to the amino acid tyramine in some fermented soy products, and if concerned can consult with a nutritional expert. Additionally, other people with a clear thyroid disorder might possibly have some problem with soy if they are not consuming adequate iodine. Moreover, isolated and concentrated soy extracts — phytochemicals from soy — are not universally recommended unless guided by a nutritional expert. But for most people as mentioned above, non-GMO unsweetened soy milk consumed in moderate amounts (about a cup a day) represents a good alternative to cow’s milk. Of course, there are other options to choose from, such as unsweetened almond milk.
Phytoestrogens and endocrine functions
The internet article also claimed that phytoestrogens disrupted endocrine function and caused infertility. A number of lines of research suggest that the infertility claim is baseless. Perhaps the most interesting study of women going through infertility treatments with reproductive technology found that the more soy isoflavones the women ate, the more likely they were to succeed in bearing children.
Effect on estrogen levels
The next problem raised was soy’s content of natural properties that are purported to affect estrogen levels, with suggestions that they might alter the menstrual cycle for pre-menopausal women. It’s unclear what these so-called properties consist of, but most likely they are the isolated phytoestrogens genistein and daidzein, which the same article actually refers to as “toxins.” This labelling is an inaccurate, misleading and thus an unnecessarily disturbing categorization. Simply put, phytoestrogens are plant chemicals that have a molecular structure similar to but not equal to natural estrogens. But to clarify this issue: phytoestrogens have only very weak estrogenic effects. In fact, 47 scientific studies found and reported that phytoestrogens have no effect on estrogen levels in normal women and there is little chance of these weak phytoestrogens altering the menstrual cycle.
Furthermore, to erase some fears of women with a breast cancer diagnosis or concerns about the danger of this disease — in large studies evaluating soy consumption and breast cancer rates researchers did not find eating soy foods led to greater risk or likelihood. Though the estrogen-like properties of soy might seem like they could increase the chance of breast cancer recurrence or mortality, current studies suggest that eating moderate amounts of soy foods is safe for breast cancer survivors. In fact, in conducted by Dr. Anna H. Wu et al. at University of Southern California, showed that women who consume approximately one to two servings of soy food each day – not isolated soy supplements — actually have a reduced risk of a breast cancer recurrence or of being diagnosed with this disease. Moreover, three studies in China and 2 studies in the U.S. provided further evidence that women who ate more soy had better survival after breast cancer diagnosis than those who ate the least soy.
Carrageenan
The litany of purported soy problems in the recent article began with the point that soymilk contains carrageenan. Carrageenan is a compound derived from algae that is used to thicken foods, especially non-dairy milks and related products. It is actually recognized as a safe food ingredient by the FDA. Adverse effects sometimes ascribed to carrageenan seem to occur only at extraordinarily high doses of this compound that exceed levels consumed by humans and beyond the amount authorized in foods. And as a matter of fact, most soymilk that you find at the grocery store does not contain carrageenan; other vegetarian thickeners may be used instead. Therefore, if your diet consists mainly of minimally processed foods, as we think it should, it will simply not contain excessive amounts of carrageenan.
Hemagglutinin
Hemagglutinin is a clot-promoting substance. It can occur in soy and other legumes, and is alleged to cause red blood cells to clump together. However, in moderate to even large soy intake the amounts in a diet do not seem nearly enough to affect red blood cells in humans. There are no records of adverse effects relating to red blood cell clumping in the Natural Medicines Comprehensive Database, which is the authoritative source of information on supplements. Nor does any appear in other scientific work we have seen. Soy is, in fact, generally excellent for the circulatory system, reducing total and LDL cholesterol.
GMO soybeans
The prevalence of genetically modified (GMO) soy in the food supply is also noted as a problem for soy milk. It is very easy to avoid GMO soy in soymilk. The major brands are all made from non-GMO soy, which is clearly marked on product packaging. If you are considering other types of soy foods, note that organic soy foods are more likely to be made from non-GMO soy.
Phytic acid
Soy is also known to contain high levels of phytic acid, which may bind to minerals and possibly reduce their absorption. However, this is only a potential problem for people who eat excessive amounts of soy and get inadequate minerals. A 2005 study showed that absorption of calcium from soymilk fortified with calcium carbonate (as many brands are) was as good as absorption of calcium from dairy milk. Interestingly, phytic acid is also known as inositol hexaphosphate, or IP-6, a well-known immune stimulating dietary supplement often given to cancer patients.
Aluminum
The internet source purports that soy contains high levels of aluminum and that aluminum is linked to Alzheimer’s disease. Actually, the idea that aluminum causes Alzheimer’s is not supported by science nor considered valid in the scientific community after considerable research.
Heat-altered proteins
In making soy protein isolates and textured vegetable proteins, soy proteins are purported to be altered in dangerous ways by heating. Since the exact nature of such dangers is not explained in the article we read, it’s hard to understand what the concern is. Ideally, however, soy protein isolates and textured vegetable proteins should represent only a very small part of your diet, which should be composed of whole foods and minimally processed products. Soy hot dogs, sausages, and other meat substitutes that might contain these substances should be an occasional treat rather than a staple of your diet.
Isoflavones
Soy contains a type of phytochemicals called isoflavones, specifically genistein and daidzein, that are alleged in this website to be toxic and to stimulate breast cancer growth. The isoflavones are in fact the phytoestrogens in soy, and they are not toxic, and certainly not problematic at normal dietary levels. In fact, they have many cancer-inhibitory properties. In some test-tube studies and in some animal studies, though, they have caused breast cancers to grow. However, animals absorb much higher levels of these molecules than humans, so they show much greater effects than would be seen in a person consuming a moderate level of dietary soy. That said, one thing that the Block Center does not approve of are supplements of isolated isoflavones for breast cancer patients. Some women take concentrated isoflavone supplements to alleviate menopausal symptoms. Because breast cancer patients can suffer severe menopausal symptoms due to their treatments, isoflavone supplements might be considered for them. It’s not been shown conclusively that these concentrated phytoestrogens are dangerous for breast cancer patients, and several studies say that they are not. However, to be on the side of caution, we do not recommend isoflavone (extracts of soy) supplements for breast cancer patients with estrogen-receptor positive disease.
Nitrate
Finally, the article points to the nitrate content of soy as another allegedly carcinogenic constituent. Nitrites, chemicals similar to nitrate, are used in preserved meats such as bacon and sausage, which are viewed as carcinogens. Soy does contain some nitrate, as do many other vegetables. In fact, though, soy contains much less nitrate than many other vegetables! If consumed in moderate amounts as part of your healthful diet, nitrates in soy are not a carcinogen.
This internet attack on soy is just one of many that you may stumble across. Much of what is said in it is misinterpreted or out-of-date science. For most people, there is no problem with eating moderate amounts of soy food. As we’ve explained, a cup of soy milk daily with your breakfast cereal or fruit is fine, along with a few servings of soy foods such as tofu and tempeh per week. More processed soy foods like frozen veggie burgers are better suited as only occasional menu additions.
But soymilk is not the only alternative to dairy milk. Grocery store shelves now contain milks from almonds, cashews, rice, oats and coconut. These are good options to consider as well. Which should you use? To begin with, stick with the unsweetened varieties of milk alternatives since several varieties are sweetened with white (cane) sugar or sucrose, which you should be avoiding. As we mentioned above, we guide people with soy allergies, those on certain antidepressants and people with thyroid disease to avoid soy. But non-dairy milks offer a variety of pleasing and healthful alternatives to cow’s milk. If you haven’t yet explored them, now is a good time to start!