Around the web we read a lot of nutrition information and one of the areas that commonly comes up is questions around soy health risks.
There is so much noise out there about different aspects of nutrition but I think one of the important things to question is where is the information coming from?
Is the article you’re reading backed by research or is the article just saying that because the person writing it read it somewhere else?
These are the questions to keep in the back of your mind when you’re reading things online because although we might all have opinions about things, it is better if there’s a bit of research to back up our claims. So let’s take a look at soy and health and any of the risks and you can decide for yourself.
Soy in the food supply
You probably know about soy milk, tofu, and tempeh, but did you know that soy is in approximately 60% of other foods in our modern food supply?
I didn’t either until I started researching.
Textured soy protein, which can be used on its own, also gets added to many meats like sausages and hamburgers, and can also get used to fortify other products. Soy protein isolate is found in many energy drinks, sports drinks, infant formula, cereals, granola bars, imitation dairy products, ice cream, cheese, and doughnuts. It’s a popular food additive because of it’s nutrient profile being seen as healthy.
Two components of soy can influence health, isoflavones and phytoestrogens. In foods the phytoestrogens are in mixtures and don’t come packaged with the isoflavones. Genistein and daidzein are derived from isoflavones in the gut, but only about 30-50% of people can effectively digest these because we need a specific intestinal microbe to do it. Vegetarians and Asian people appear to have the best ability to digest them, who knows why?! (1)
Fermented Soy Is Best
Many of the products that do contain soy do not contain fermented soy and there is a BIG difference in the way the body metabolises and uses them. Most of the negative outcomes of soy have come from studies done with non fermented soy. Fermented soy on the other hand has been shown to exhibit some health benefits. Fermented soy products inlcude miso, soy sauce, natto, and tempeh. Non fermented soy products include soybeans, dehydrated soy beans, soy flour, soy sprouts, soy milk, tofu, okara, and yuba. Yes tofu is non fermented, something many people don’t realise. I ate it for years and never knew.
Fermented soy is high in B12 and can aid pernicious anemia, contains the probiotic lactobacillus acidophilus, and exihibits positive effects on blood pressure. It is the fermented soy that exhibits antioxidation, antimutagenic effects, and reduction of symptoms of post-menopause. Fermented soy displays high antioxidant activity, as well as cytotoxic activity (cell death) toward cancer cells. (1)
Soy Health Risks. True Or False?
Let’s explore a few different areas and some of the info I came across.
Soy and Antinutrients
All beans and legumes do contain some antinutrients. Antinutrients are bioactive compounds that have an adverse affect on various nutrient bioavailability. These compounds include trypsin inhibitors, chymotrypsin inhibitors, a-amylase inhibitor, phenolics/tannins, saponins, phytohemagglutins (lectins), phytic acid/phytates, flavonoids, goitrogens, and oxalic acid.
This is not all bad because many foods contain some of these compounds, for example spinach contains oxalic acid, and cruciferous veggies contain goitrogens. Adzuki beans, lentils, and chickpeas contain the least amount of inhibitors. Kidney beans and soy, the highest. Soaking, cooking, sprouting and fermenting beans and legumes helps reduce many of the inhibitors as well. (2)
Although these compounds may sound bad, many of them do exhibit beneficial properties to health as well. (2)
Anyway, back to soy…
Phytoestrogens and hormones
One of the most significant areas that are affected by phytoestrogens are hormones. Because the phytoestrogens can bind to cells, various hormones can be disrupted. This may have an effect on things like lactation, reproduction, fertility, and sex specific behaviour. Phytoestrogens can manipulate the biosynthesis of various steroid hormones in the body and displace other ones. (3)
There is some speculation that soy isoflavones can be disruptive to the female reproductive health, as it suppresses circulating estrogen and progesterone levels. Caution in eating soy should be taken for women attempting to become pregnant or experiencing menstrual cycle irregularities or hormonal upsets.
This may also be true for men experiencing fertility problems and although fertility issues are likely complex, soy is currently under the radar as a possble contributor. (3)
Soy and Cardiovascular Disease
In 1999 the US Food & Drug Administration made the announcement that “daily consumption of soy is effective in reducing the risk of coronary artery
disease”. (3) Since then we have seen the explosion of soy into the food supply, and not the fermented kind.
When it comes to cardiovascular disease I found one recent study that showed that a higher consumption of soy nuts and textured vegetable protein over 12 weeks in people with metabolic syndrome helped to slightly reduce lipid profiles and apolipoproteins. (3)
Although the statement by the FDA was made 14 years ago, there has been very little convincing evidence to suggest that soy has any effect on heart disease at all. (1)
Soy & Breast Cancer
It is well established that increased levels of estrogens contribute to breast cancer development. Depending on the circumstances it appears that genistein can have a proliferation or an anti-proliferation effect. One study showed a 35% decreased risk of breast cancer with elevated levels of genistein but other studies have failed to support this conclusion. (3) Another study with 5042 Chinese women showed decreased risk of death or reoccurance associated with breast cancer. (5)
I’d say there is still not enough evidence to suggest a conclusion either way.
Another review stated that there were some positive associations to soy in regard to breast cancer, but it’s important to note that ALL of these studies are in Asian populations. In my eyes there are two important points to draw from this:
1. Asians mostly eat fermented soy and I mentioned above how that is associated with beneficial outcomes.
2. The Asian traditional diet is VERY different to a standard Western diet. Asians intake of isoflavones is anywhere between 25-50mg a day, Westerners is 1mg day. (5) This might explain why they can digest it more readily, being their exposure probably starts early on in life too.
In another study genistein was shown to inhibit pathways of growth and cell proliferation and limit protein tyrosine kinases, which may slow down tumor growth, particularly in relation to breast cancer. The limiting effect on protein tyrosine kinases may also have a neuroprotective affect and improve cardiovascular disease. Overall genistein and other isoflavones were shown to help regulate cell growth and be semi protective. (3)
I guess the verdict hasn’t really been concluded on whether or not it helps breast cancer or causes it. Again I think it appears to depend on the circumstances.
Soy and Inflammation
The mechanisms in soy daidzein and genistein have been shown to reduce inflammatory markers IL-6, TNFa, sTNF-R1 & 2, and CRP. Again this study was conducted on 1005 Chinese women (Asian). The same mechanisms also seemed to reduce oxidative stress. (6)
In this study it showed the following positive comparisons:
- 27% reduced IL-6 = 37% decreased risk of lung cancer
- 32% reduced IL-6 = 25% decreased risk of type 2 diabetes
- 15% reduced TNFa = 18% decreased risk of acute myocardial infarcation (heart disease) (6)
Clearly there is something in the Asian diet that exerts positive outcomes compared to that of our Western diet. Likely it’s because of everything else that gets eaten too.
So what’s the verdict. Soy health risks true or false?
Like all foods, soy has been shown to have both pros and cons, it all depends on your level of exposure and in what form it comes.
Being that most people are likely consuming too much of it within the food supply, it certainly isn’t a good thing. Another important component to be aware of is that it does have endocrine disrupting capabilities. If women who are pregnant, breast feeding, or trying to concieve should likely avoid it, then that makes me question the effect for the rest of us. Our hormones are really the drivers of many of our bodys functions and if soy is going to mess with those, then where might that leave us and our health??
That said, having a bit of tofu or a miso soup on the odd occasion isn’t going to kill you. My husband likes to drink soy milk because he can’t drink milk. I use tamari (wheat free soy sauce) in cooking, I enjoy miso soup sometimes, and I may have the odd bit of tempeh with a friend who is vegetarian. But these days that’s about the extent of our consumption and that’s the way I intend to keep it.
What about you, do you consume soy products? And will you continue to do so after reading this?
I hope you found this helpful so please share it around to inform others too.
As you can see a lot of work goes into writing an article like this so your help in sharing it is much appreciated 🙂
1. Chen KI, Erh MH, Su NW, Liu WH, Chou CC, Cheng KC. Soyfoods and soybean products: from traditional use to modern applications. Appl Microbiol Biotechnol. 2012;96:9–22.
2. Siddiq M. Uebersax MA. Dry Beans and Pulses. Wiley-Blackwell. 2012. pp.179, 199, 359.
3. Patisaul HB, Jefferson W. The pros and cons of phytoestrogens. Front Neuroendocrinol. Oct 2010; 31(4): 400–419.
4. Bakhtiary A, Yassin Z, Hanachi P, Rahmart A, Ahmad Z, Jalali F. Effects of Soy on Metabolic Biomarkers of Cardiovascular Disease in Elderly Women with Metabolic Syndrome. Archives of Iranian Medicine. Aug 2012; 15(8)
5. Mourouti N, Panagiotakos DB. Soy food consumption and breast cancer. Maturitas. 2013;76:118– 122
6. Hui Wu S, Ou Shu X, Chow W, Xiang YB, Zhang X, Li HL, et al. Soy Food Intake and Circulating Levels of Inflammatory Markers in Chinese Women. J Acad Nutr Diet. 2012 July ; 112(7): 996–1004.