Soy – the bottom line
Contents: phytoestrogens – far from estrogen | protection from heart disease | soy for cancer prevention | soy for infants | soy for men | soy and the thyroid gland | absorbing minerals from soy | reducing heat flashes in menopause using soy | bone density and osteoporosis | processed soy products | summary
The natural ingredients in soy that have been both highly praised and excessively slandered are phytoestrogens, also known as isoflavones. Phytoestrogens are a group of substances similar to the sex hormone estrogen, only that their affinity is a thousand times lower than that of estrogen. The American Nutrition and Dietetics' (ADA) review that specifically refers to isoflavones clarifies that their effect in soy is not harmful and may even serve as a protection against cancer (details below).
One of the main problems in reviewing studies about soy is that many studies do not deal with actual soy but rather soy preparations containing extremely high concentrations of phytoestrogens. Such studies need to be addressed with considerable care, since the effect of a substance depends on its concentration, and sometimes different concentrations of a certain substance show different results. In this article we will review the rumors surrounding phytoestrogens and other suspicions that cling to soy, as well as address some of the prominent advantages of soy as a successful vegetal parallel to animal products. It is entirely possible to sustain a healthy vegan diet entirely without soy, but there is no reason to avoid it, either. Various soy products such as soymilk and tofu are a good source of calcium in a vegan diet. Much like other legumes, soy contains a substantial quantity of iron, zinc and high-quality protein, as well as dietary fiber and antioxidants.
Many studies link soy intake with protection of the heart and blood vessels, improved elasticity of the arteries, and lowered cholesterol levels. One of the reasons for these effects is the isoflavones and phytosterols in soy, which are found in small amounts in other vegetal foods as well (such as legumes and flax). However, the most powerful effect of soy on heart disease derives from the fact that it replaces animal products, the consumption of which may cause these diseases. Tofu and textured soy protein (TSP) are often consumed as a replacement for meat products, which are rich in saturated fats, cholesterol, and, at times, even traces of heavy metals, hormones, antibiotics, and free radicals (oxidant substances that damage the blood vessels and are linked to cancerous processes). Soy, on the other hand, does not contain cholesterol, has very little saturated fat, and is rich in antioxidants and dietary fiber. These attributes have been found to be linked to a reduced risk for heart disease and various types of cancer, as well as a general decrease in the risk of premature death.
While some people fear that soy may be linked to the development of cancer, the world's leading health organizations claim that soy may, in fact, prevent cancer. In 2012, the American Cancer Society (ACS) published updated guidelines for a cancer-preventing lifestyle. According to these guidelines, which were based on the most up-to-date research in the field, it seems that the intake of soy may prevent cancers related to the reproductive system: breast, uterus, and ovarian cancers in women, and prostate cancer in men. The ACS’s summary states the following:
And what about men and women who have recuperated from cancer and now follow a strict diet in order to prevent the recurrence of the disease? According to the American Cancer Society, there is no hard evidence on soy's influence in preventing or causing a recurrence of the disease in such cases, yet it is plausible that soy has a positive effect on breast cancer patients treated with Tamoxifen (a common hormonal treatment for preventing the disease's recurrence). Organizations such as ADA and the World Cancer Research Fund published similar views on this matter. The reason for soy's anticarcinogenic effect is that phytoestrogens may bind to receptors on tissues that respond to estrogen, thus blocking estrogen's effect on these tissues; that is, phytoestrogens have an anti-estrogen effect. (High levels of estrogen are associated with the occurrence of cancer).
In some animal studies a negative effect of phytoestrogens was found. However, this effect was probably due to the very large amounts of phytoestrogens used, amounts that are irrelevant to our diets (even if we eat three servings of soy a day). Studies done in the Far East found a protective effect for soy consumption against breast cancer, while Western research did not find any influence either way. One of the explanations is that soy consumption in the Western studies was lower, as soy consumption is typically greater in the East.
To summarize, soy consumption is not related to an elevated risk for cancers of the reproductive system, and may even protect against them. Furthermore, women who are in a risk group for breast cancer also tend to be in a risk group for heart disease, and therefore soy consumption is especially advisable for them.
The most recommended way to feed a baby is by breastfeeding. Vegan mothers that cannot breastfeed, for any reason, can use a soy-based infant formula wholeheartedly. True, the Ministry of Health guidelines prefer a formula based on cow's milk, but they also state that there is no problem with using a soy-based infant formula. Long-term studies found that there are no developmental differences between infants fed on vegan or dairy formulas versus infants that nurse. (Nursing infants are smaller in the first year or two but the gap narrows later on). There are animal studies that show early puberty in rats fed with soy, yet human studies (including an Israeli study that followed infants for twenty years) did not find such a connection.
In any event, it is important to clarify that while there is some controversy related to feeding an infant strictly on soy formula, there is no controversy related to combining soybeans and their products in the infants' daily menu at the phase in which infants start eating solid foods. In Japan tofu and miso are a part of infants' diet beginning at six months of age. If this has any health implementations, they are for the better – protecting girls from breast cancer later in life.
Premature puberty is a problem that has been getting worse in the Western world and is related to various environmental contaminants, an increase in obesity, and excessive consumption of animal products. No connection to soy consumption has been found.
Read more about soy in infants' menus and a suggestion for a vegan diet for children.
There are two known cases of men that developed breast tissue after consuming extreme amounts of soy – 12 servings per day and more. In both cases stopping the overconsumption of soy resulted in the degrowth of the breast tissue and return to the original physical state. All studies relating to the male reproductive system have shown that when soy is consumed in a normal amount (1-3 servings a day), it has no effect on the male reproductive system in general and on the sperm count in particular. This conclusion is based on a review of studies on the subject since 2010. These studies have all reached similar conclusions, apart from the two cases mentioned above, plus the studies (also mentioned previously in this article) in which men and rodents were given high concentrations of phytoestrogens that cannot be acquired by consuming a normal amount of soy.
No connection between daily soy consumption and damage to the function of the thyroid gland has been found. However, people who suffer from hypothyroidism and are not receiving medication to balance their thyroid level, and who then start consuming more soy in their diets, need to make sure after a few months that there has been no change in the gland's functioning. People who suffer from hypothyroidism and receive medication can eat soy without fear, but they should eat the same daily amount recommended for people in general. Changes in soy consumption should be followed by changes in medication dosage since soy protein affects the medication's absorption. These recommendations are true as well for other types of foods that are considered problematic in hypothyroidism, such as crucifers (plants of the cabbage family), which are suitable for the general population but not for those with hypothyroidism.
Similarly to other legumes and whole grains, soy and other vegetable foods contain dietary fibers and phytate, which obstruct the absorption of iron, calcium, zinc, and other minerals, and to some extent the absorption of protein as well. And yet, the absorption of calcium from soy is identical to that from cow’s milk (approximately 30%, a good absorption level). According to a number of studies, the absorption of iron from soy is relatively high as well, for plant-based iron (around 30%). Cooking, soaking, and sprouting considerably increase the absorption from all legumes, soy among them. Combining these foods with fresh fruits and vegetables, especially those rich in vitamin C (peppers, parsley, and others), also improves mineral absorption. Furthermore, there is evidence for improvement in mineral absorption with long-term consumption of soy, as well as generally with a vegetarian diet, as the body adapts with time.
Phytate is a notorious substance in the world of nutrition due to its tendency to disrupt mineral absorption, so much so that it is referred to as an anti-nutrient in some of the articles in the field. That said, there are a number of articles showing the health benefits of phytate, such as the prevention of various cancerous processes, the reduction of cholesterol levels, and even the prevention of kidney stones.
There is evidence suggesting that phytoestrogens may help reduce menopausal symptoms such as hot flashes, although information on the subject is not entirely consistent. The reason for the possible benefit is that at this age the concentration of body estrogen decreases sharply, and it may be that phytoestrogens can serve as a substitute. With regard to regular consumption of soy-based products, there is hardly any evidence for either a positive or a negative effect on the symptoms.
There is some evidence pointing to improved bone density and prevention of osteoporosis among those who consume soy on a regular basis and among women who use phytoestrogen products during menopause (where reduced levels of estrogen is linked to reduced bone density). There are a number of studies that show that soy protein may cause an increase in bone density, though most of the studies do not show a significant effect. What is beyond dispute is that soy does not cause any negative effect on bone health.
Adding to the complexity of the subject of bone health, bone density is enhanced not only by adequate calcium and estrogen levels but also by eating enough fruits and vegetables, reducing one's salt and animal protein consumption, and first and foremost by bone-building exercise.
In health food stores (and increasingly in ordinary shops and supermarkets), various soy-based foods can be found such as cream cheese, yellow cheese, desserts, and yogurt. Compared to less processed soy products (such as tofu, soymilk (unflavored), edamame, and textured soy protein), these foods are more problematic healthwise. The problem with these products is not related to soy but rather to the surrounding ingredients. The soy cheeses currently sold in Israel are rich in fat (largely hydrogenated), alongside a large dose of salt. Furthermore, most desserts and yogurts contain a large amount of sugar and at times various preservatives and stabilizers as well. These products can serve as "training wheels" that may assist in one's transition to veganism, but as with processed foods in general, they are not recommended on a daily basis. They should be regarded as a treat or snack rather than as basic item in one's diet.
Soy in general and its phytoestrogens in particular have been studied for over 20 years and make a platform for many rumors, good and bad. Excessive intake of soy and phytoestrogen products is unadvisable, since their health implications at high dosages are not fully clear. Studies dealing with phytoestrogen products should be viewed skeptically because they are often funded by the nutritional supplements industry. No harmful effect was found for the consumption of 1-3 servings of soy a day throughout life. Any effect of soy on human health is a positive one -- protection from heart disease, cancer, and possibly from osteoporosis as well. Advice about using soy can be found in the website's Tofu and Soy pages.
Those who wish to deepen their understanding of the subject are welcome to read clinical nutritionist Orit Ofir's article in Ha'aretz, "Why soy is not a trendy milk replacement but basic food", and to watch her lecture about soy as a possible protective element for women against breast cancer – and not, heaven forbid, the cause of it (as related in "Nutrition 2014", the scientific convention on nutrition in Israel).
For those that wish to take their understanding even further, it is recommended to read the extended article by the vegan clinical nutritionist Jack Norris: Soy: What's the Harm?
American Cancer Society Guidelines on Nutrition and Physical Activity for Cancer Prevention, 2012
American Cancer Society Guidelines on Nutrition and physical activity guidelines for cancer survivors, 2012
The Bottom Line on Soy and Breast Cancer Risk - EXPERT VOICES Timely insight on cancer topics from the experts of the American Cancer Society Marji McCullough, ScD, RD, August 02, 2012
World Cancer Research Fund / American Institute for Cancer Research. Food, Nutrition, Physical Activity, and the Prevention of Cancer: a Global Perspective. Washington DC: AICR, 2007
Report on the 8th International Symposium on the Role of Soy in Health Promotion and Chronic Disease Prevention and Treatment J. Nutr. April 2009 vol. 139 no. 4 796S-802S
Soybean isoflavone exposure does not have feminizing effects on men: a critical examination of the clinical evidence, Fertility and Sterility, Volume 93, Issue 7, 1 May 2010, Pages 2095–2104
Dietary roles of phytate and phytase in human nutrition : A review. Kumar, V. et al., Food Chemistry, 120(4), pp.945–959. 2010
Use of Soy Protein-Based Formulas in Infant Feeding. Bhatia, J., Greer, F., & Care, P. doi:10.1542/peds.2008-0564
Safety of Soyfoods, V. Messina, MPH, RD, Vegetarian Nutrition Dietetic Practice Group of the Academy of Nutrition and Dietetics, 2012
Soy isoflavones for osteoporosis: an evidence-based approach Taku, K. et al., 2011.. Maturitas, 70(4), pp.333–8.
Effect of soy isolate protein and resistance exercises on muscle performance and bone health of osteopenic/osteoporotic post-menopausal women. Shenoy, S., Bedi, R. & Sandhu, J.S., 2013 Journal of women & aging, 25(2), pp.183–98. 2013