This is the unedited version of my soy article from Edition 1 of
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Controversy and Confusion
As vegan dieticians Davis and Melina point out in their excellent book Becoming Vegan “some of the science on soy has been distorted by people who misunderstood or sensationalised the research when scientific articles have been published – and then misinterpreted – leading to rumours that spiralled out of control.” The authors also point out that the bad press may in part be due to the fact that “soy foods pose a threat to the animal products industry.”
Soy because quite popular in the 1990’s, with soymilk finally making its ways into supermarket fridges alongside cow milk, in the same kind of packaging used for cow milk. To add insult to injury, blind taste tests were proving that many consumers found soy preferable to cow milk. Most of the anti-soy articles I’ve read online can usually be traced back to groups who are promoting the consumption of a meat and dairy based diet because they represent the interests of cattle ranchers and dairy farmers.
Soy and Digestion
You may have heard that soy contains ‘anti-nutrients’ that will mess up your digestion and reduce your absorption of nutrients. Some of these ideas are based on studies involving the consumption of raw soybeans by non-human animal species. Unless well-cooked (or fermented), soybeans can inhibit trypsin, a digestive enzyme, making them difficult to digest. But humans don’t consume raw soybeans, and we aren’t rats or parrots, so these studies aren’t really very useful to us!
One of the so-called anti-nutrients in soy are saponins. Saponins are those soapy suds you see when rinsing your legumes, and yes, they can be irritating for the gut if you consume excessive amounts, but if rinse your legumes and cook them properly, you will be fine. Saponins have incredible immune-boosting, liver-protecting and cholesterol-lowering effects, and have been found in more than 100 families of plants, some of which have truly astonishing health-effects, like the ginsengs. A study published in 2010 in Fitoterapia, a medical journal dedicated to medicinal plants and their bioactive ingredients, says that there are at least 150 different kinds of saponins with significant anti-cancer properties.
Phytic acid is another ingredient in soy that has been called an “anti-nutrient” because it hinders the absorption of minerals, in much the same way tannins in tea do. Some anti-soy writers quote old studies done on puppies and rats that suggest phytates soften bones, but more recent studies done with humans show that low phytate diets are linked with osteoporosis, whereas high phytate diets seem to provide protection against osteoporosis. This is perfect example illustrating why we shouldn’t be testing on animals: aside from being a cruel and gross violation of animal freedom and rights, all animals are different and what is relevant in one species doesn’t necessarily translate to another.
A Nutritional Overview
A favourite clinic resource of mine is the book Healing with Whole Foods – Asian Traditions and Modern Nutrition. The author, Paul Pritchard, says that soy was first described in Chinese manuscripts in 2800 B.C, and that soybeans are often called the “beef” of China due to their extensive use and high protein content (38%). In Asian traditional medicine, soy is a remedy used for boosting milk production in women, and for treating dizziness, childhood malnourishment, skin eruptions, constipation, and fluid retention. Soybean sprouts are used to treat spasms, arthritis, indigestion, and some types of cough and infection.
From a western nutritional perspective, soy is nutritionally similar to other legumes, but it’s lower in carbohydrates and higher in protein and fat. The fat in soybeans is mainly polyunsaturated, and includes alpha-linolenic acid, making soybeans one of the few good plant sources of omega-3 fatty acids. Whole soybeans are a rich source of carbohydrates called oligosaccharides, which stimulate the growth of healthy gut bacteria and help improve our cholesterol levels. Several Chinese and Japanese studies have shown a 50% reduction in the likelihood of heart disease in those who consume two servings of soy per day. The protein in soy is highly digestible, with an amino acid profile closely matching human requirements. Legumes such as soy contain dollar-for-dollar more protein than meat, and are the cornerstone of every Blue Zones diet in the world. Blue Zones are places in the world where the longest living people reside.
High in B-vitamins, especially niacin, pyridoxine and folic acid, soy is also a good source of minerals such as calcium, iron, magnesium and copper, in spite of the absorption inhibitors commonly touted as anti-nutrients. Soymilk and tofu often have calcium added to them, so they are particularly rich calcium sources and can be a very useful addition to an otherwise whole-foods diet. It used to be thought that the iron from soy was poorly absorbed but this has since been discounted. The iron in soy is present in a form called ferritin, which is very well absorbed.
Some of the anti-soy propaganda being circulated has targeted soy-based infant formulas, suggesting that they are difficult to digest and may lead to health problems but there is no conclusive evidence available to support these claims and most experts are confident in recommending soy-based formulas. In fact, some of the most consistent evidence emerging from soy research suggests that women who consume soy in childhood and their teen years have greater protection from breast cancer.
Soy and Thyroid Health
Should you avoid soy if you have thyroid problems, and can soy cause thyroid problems? Concerns about the effect of soy on thyroid function have arisen mostly from studies on animals. In humans, the story if very different, with evidence clearly showing that soy doesn’t affect thyroid function in healthy people. In fact, population studies have shown that soy can be beneficial for the thyroid, by protecting us from thyroid cancer.
Soy can only cause thyroid problems if you are deficient in iodine, which can be a problem amongst the vegan community. This is due to the goitrogens present in soy. Goitrogens are also present in millet, some herbs, and cruciferous vegetables like cauliflower, cabbage, kale and brocolli. If you have sufficient iodine in your diet, these goitrogen-containing foods won’t cause you any trouble at all. On a vegan diet, you can get iodine from many salts and bread which have iodine added to them. Iodine is also found in seaweeds or sea vegetables, but the amounts vary from one batch to another, and can also be affected by drying and storage methods.
If you have an existing hypothyroid problem and you are on medication, you can still eat soy, so long as you are monitoring your thyroid and you have your doctor’s support. The trick to balancing soy intake with medication is to be eat roughly the same amount of soy foods daily, and to take your medication away from meals.
Menopause: Soy or Premarin?
A study called the Women’s Health Initiative study found that menopausal women taking hormone replacement therapy certainly benefited from improved bone health and less menopausal symptoms such as hot flashes, but there were some rather unfortunate side effects. In fact, these side-effects were so severe, that the trial was called off, due to the high rates of breast cancer, cardiovascular disease, and overall harm.
The hormone replacement therapy being used in this study was, of course, premarin, sourced from pregnant mare’s urine. For most of their 11-month pregnancies, these horses are confined to stalls so small that they cannot turn around or take more than one step in any direction. They are forced to wear rubber urine collection bags which cause chaffing and lesions. When their foals are born, the horses are re-impregnated. This cycle continues for about 12 years. Some of the foals are used to replace their exhausted mothers, some are adopted out, but most of them end up in slaughterhouses, an unwanted by-product of the HRT industry.
There are two types of estrogen receptors in the body: alpha receptors and beta receptors. Animal-sourced estrogen binds to alpha-receptors in the liver, causing the liver to produce the clotting factors that lead to blood clots in the heart, brain, and lungs (hence the increased cardiovascular risk with HRT). A safer and kinder alternative to animal-sourced HRT are phytoestrogens, or plant-based estrogens, which preferentially bind to the beta receptors. Phytoestrogens are found in a wide range of grains, seeds, legumes, yellow and white fruits and vegetables, and medicinal plants.
Soy contains some very useful phytoestrogens called isoflavones. While these aren’t ‘real’ estrogens, they do have a very similar shape, chemically, allowing them to slot into tiny receptor sites in our cells, a little bit like a key sliding into a lock. Being 1000 times weaker than human estrogen, isoflavones can’t unlock all of the estrogenic functions available to us, but in an estrogen deficient environment like menopause, something is better than nothing, and phytoestrogens can reduce menopausal symptoms like hot flushes and headaches. Human bone cells have beta estrogen receptors, and soy phytoestrogens seem to significantly increase bone mineral density in menopausal women. In studies on bone density and soy, soy appears to prevent bone loss while enhancing new bone formation, resulting in a net gain of bone mass.
The amazing soy-based receptor-site tricks that are so beneficial during menopause, also come in very handy during our menstruation years. One of my favourite clinic resources for my female clients is Women, Hormones and the Menstrual Cycle, written by author Ruth Trickey, an Australian naturopath. As Ruth says “When menstruation women have a high intake of soya products, studies have shown that they ovulate later, and the period tends to become lighter and shorter. Soy isoflavones in combination with phytoestrogenic herbs can be used to reduce pre-menstrual symptoms such as headaches and migraines.”
Soy and Breast Cancer
The reason why breast cancer becomes a problem when we use animal-sourced HRT medications, is because breast cancer is a hormone-dependent cancer which thrives in the presence of estrogen. This is where phytoestrogens can come in very handy. As the delightful Dr Greger says in his nutritionfacts video Who shouldn’t eat soy? “As you drip more and more soy compounds on breast cancer cells in a petri dish, less and less actual estrogen is able to bind to them.” The much weaker, gentle-acting phytoestrogens in soy slot into the cell receptor sites and block real estrogen from being taken up by the cell. This is called competitive inhibition and is one of the theories behind why so many studies have shown a connection between soy and a reduced incidence of cancer.
Mind you, there is a big difference between what happens in a petri dish and what happens in a human body, and even amongst the researchers there is a lack of agreement about the role soy plays in breast cancer. Keep in mind that some of these researchers are being paid by anti-soy campaigners, while others are working in the soy supplement industry. Some of the more negative research outcomes have led to concern amongst the general public that soy might cause or contribute to breast cancer, but vegan dieticians, doctors and naturopaths like myself are very comfortable with the existing overall weight of evidence suggesting that soy doesn’t cause breast cancer and may even may a protective role.
It’s worth noting that the caution given by the researchers who published a study based on 5,000 breast cancer survivors in the Journal of the American Medical Association in 2009, titled Soy Food Intake and Breast Cancer Survival. They concluded that “soy food consumption was significantly associated with decreased risk of death and recurrence,” for women with breast cancer, with the emphasis being on soy foods, not soy isoflavone supplements: “[T]he potential benefits are confined to soy foods, and inferences should not be made about the risks or benefits of soy-containing dietary supplements. Patients with breast cancer can be assured that enjoying a soy latte or indulging in pad thai with tofu causes no harm, and, when consumed in plentiful amounts, may reduce [the] risk of disease recurrence.”
Nutrition research is complex, and some of the mixed messages we we’ve heard from soy researchers have arisen due to the difference between animal test subjects and humans, tests taking place in petri dishes and test tubes instead of real human bodies, and conclusions drawn from research based on isolated ingredients taken from soy verses soy as a whole food, just to name but a few of the variables! While more research needs to be done, up to date position statements from cancer councils around the world agree that a moderate consumption (1-3 servings) of daily soy is perfectly safe.
While I continue to keep my eyes open for new research into soy, I feel confident soy is a safe and beneficial food. Given the weakness of phytoestrogens relative to human estrogens, I seriously doubt they can do us much harm, while their role as competitive inhibitors may prove highly beneficial in the management of estrogen-sensitive cancers.
Soy and Men’s Health
Unfortunately, some men avoid soy because they believe it will give them breasts or feminise them. Yes, soy does contain estrogen-like compounds called isoflavones, but isoflavones are 1000 times weaker than human estrogens! Some of the misinformation seems to have come from studies based on two men who ate almost nothing else except soy, and not surprisingly, they developed some health problems. When their soy intake was reduced, their health returned to normal. Many things that are very good for us in small doses can become problematic when we consume them to excess.
A comprehensive analysis of all the research done into the effect of isoflavones on men was published in the international medical journal, Fertility and Sterility. It found that soy does not affect testosterone or estrogen levels in men, and does not have a feminising effect on men. Soybeans have been part of Asian diets for many centuries, with no evidence of any negative impact on reproduction in these populations. In fact, soy is highly beneficial for men: an analysis of 14 studies published in the American Journal of Clinical Nutrition showed that increased soy intake reduced the risk of prostate cancer by 26-30%. People in Japan and urban areas of China consume around 1 ½ servings daily on average, and their prostate cancer rates are four to six times lower compared to western populations.
By comparison, animal products appear to increase the risk of prostate cancer. The link between high-calcium diets and prostate cancer seems fairly solid, but more research will need to be done into the prostate cancer-dairy link before this is accepted as a fact amongst the medical community. Studies have to be replicated over and over again, many times, and considered from many perspectives before good conclusions can be made. Having said that, I’d like to quote PCRM on the prostate cancer-dairy link: “Although somewhat fewer studies have addressed the association between milk and prostate cancer, their demonstrated effect strength and consistency of evidence approach those relating alcohol to breast cancer risk, an association that is now widely accepted and incorporated into the Dietary Guidelines for Americans.” PCRM is the Practitioners Committee for Responsible Medicine. Based in America, PCRM is an international organisation combining the expertise of more the 12,000 doctors who promote plant based diets, prevention over pills, and modern alternatives to the archaic use of animals in medical education and research.
The vast majority of GMO soy is fed to animals, whose poor bodies seem to become (in a process called bioaccumulation) end-place storage-sites for a multitude of toxic chemicals in our environment. While there hasn’t been a lot of credible research produced about the health-risks associated with GMO foods, I err on the side of caution by sourcing organically-grown soy. There are some wonderful lists called the Clean 15 and the Dirty Dozen, created by the Environmental Working Group, that describe the most and least pesticide-contaminated foods.
There was a study on glycophosphates, (the chemicals used on genetically modified soy), featured in a medical journal called Food Chemical Toxicology (Sept 2013) that found glyphosate can activate estrogen receptors at a few parts per trillion, increasing the growth of estrogen receptor positive human breast cancer cells. Keep in mind this experiment took place in a petri dish, and this is only one study, but you can see how the soy-estrogen issues could be possibly be complicated by factors such as this. Maximum residue levels used in the GMO industry are set at parts per million, and the research so far seems to indicate that the protective benefits of soy outweigh any negative impact from these chemicals, but we obviously we need more studies before we can come to any conclusions.
Intestinal Bacteria and Soy
Soy doesn’t work the same way for all of us. For example, if you are a westerner, you can’t assume that any findings based on soy research done on Asian populations are going to be relevant to you, because your genetics and the bacterial community in your intestines is completely different. When you grow up eating a food, you are cultivating the exact intestinal bacteria needed to digest it. To function as phytoestrogens, the isoflavones in soy have to be converted or ‘metabolised’ by intestinal bacteria into a compound called equol. While 50% of Asians contain equol-producing bacteria in their intestines, only 25% of westerners have the same capacity. No wonder there has been so much inconsistency in the studies done on soy, and so much confusion!
The take-home message here is that if you want to get the best out of phytoestrogenic foods like soy, it pays to look after your intestinal health. If we don’t eat a food, we aren’t feeding the bacteria needed to break it down, so the first step to cultivating the bacteria needed to metabolise isoflavones, is to begin eating good quality whole-food sources of soy on a regular, consistent basis. When I prescribe phytoestrogenic herbs, I encourage my clients to improve their diet by consuming more natural fibre, because fibre is the food that our helpful intestinal bacteria thrive on. This means eating more plant-based whole-foods, rather than animal products and refined foods. Animal products contain no fibre at all, and refined foods (eg packaged foods, junk foods, lollies, cakes etc) contain little or no fibre. Like antibiotics, these fibreless ‘foods’ create an intestinal environment that can suppress the growth and wellbeing of the healthy bacteria needed to metabolise isoflavones and convert them into equol.
There was a small study published in the Journal of Nutrition in 2006 which found vegetarians are more likely to be equol producers than meat-eaters, so that bodes well for the vegan community!