What is soy: Soy is a bean native to East Asia, and is widely used in a variety of dishes. Soy is rich in complete protein (as discussed in this article), so it provides a wonderful way for those following a plant-based diet to reach their daily protein needs.
Soy has been a topic of controversy for decades. In this article I’ll be discussing evidence-based research regarding soy food in many facets of health.
Common Soy Foods
Edamame: immature soybeans in their pods, eaten before they harden. Edamame is commonly eaten steamed, or added to stir fries, salads, pasta and many other foods.
Tofu: Made from mature, white soybeans that are boiled, curdled and pressed into blocks (a similar process to cheese-making).
Tofu comes in a silken or soft form (best for desserts, smoothies and sauces), medium firm (best used for stir fries or baked), and firm or extra-firm (very versatile, can be battered, baked, pan-fried, stir-fried, deep-fried or glazed). Medium, firm, and extra-firm tofu should be pressed between a towel before cooking to get rid of the excess liquid. I would suggest pressing for at least 10 minutes before cooking
*Tip: For extra-porous tofu (best for soaking up sauces and marinades) freeze firm or extra-firm tofu in slices, then marinate and cook as usual. The porous tofu will soak up more of the flavour from marinades and sauces!
Tempeh: Tempeh is made of whole, fermented soy beans, giving it a higher protein and fibre and lower fat content than tofu. It has a denser, more hearty texture and slightly nuttier flavour than tofu. Tempeh is commonly used pan-fried, in stir-fries, salads, baked, or in sandwiches.
Soy milk: Made by soaking and boiling soy beans, then blending with water and filtering out the remaining particles. Soy milk contains 7g of protein per cup and 2g of fibre, making it one of the highest sources of protein when looking at plant-based milk alternatives. When using plant-based milk alternatives, try to stick to the unsweetened versions so you can control the sweetness yourself!
Soy protein isolate: This is the isolated and extracted protein part of soy, and is often used as powders for plant-based protein powders. Just 30g of this protein contains 24g of protein. However, this concentrated amount of protein generally isn’t required when following a whole-foods, plant-based diet. Supplements like protein powders should be saved for those days when you need a super convenient protein kick, or if you have higher protein needs than the general population.
Soy-protein meat alternatives: These include (but aren’t limited to) veggie burgers, chicken substitutes, and other meat alternatives that are often made out of soy protein, but typically are heavily processed with a lot of added sodium and fats. These are wonderful if you’re craving them, are in need of something quick and easy, or if you’re transitioning to a more plant-based diet, but probably not something I would recommend eating every single day. Try to stick to whole-food protein sources most often with things like this used occasionally.
Soy Nutrition Profile
Soy food consumption is not necessary when following a plant-based diet, however, it may actually have some health benefits. Soy food products are also extremely versatile, and can add great texture or flavour to a meal when cooked properly.
Using extra-firm tofu as an example, ¼ of a block (88g) provides 14 grams of complete protein (read about complete protein here), 7 grams of fat (most of which are monounsaturated and polyunsaturated), 6% of your daily calcium and 15% of your daily iron.
Common myths about soy
Soy and breast cancer: One of the controversial aspects of soy foods is the presence of isoflavones. Isoflavones in soy can bind to the body’s estrogen receptors, particularly beta estrogen receptors. Many people have the common misconception that this leads to an increase in estrogen in the body, however, binding to these receptors means that these isoflavones can have the beneficial effects of estrogen without actually influencing hormones.
Extensive research has been done concerning women and soy food consumption, showing that moderate consumption of soy foods of 1-3 servings per day may protect women against breast cancer. For women who have had breast cancer, soy foods have been shown to reduce the risk of recurrence and death from the disease in certain types of breast cancer.
Soy and men: A common misconception of soy foods is that they will negatively impact men (particularly, giving them “man boobs”). This theory largely stems from studies of men who consumed astronomical amounts of soy per day- about fourteen to twenty servings daily. One of these men consumed virtually all of his calories from soy, and the other consumed 3 litres of soy milk daily. This resulted in health problems such as enlarged breast tissue and loss of libido. In both cases, when the soy intake was reduced to normal levels these health problems disappeared. The isoflavones discussed previously do not play a role in sexual development, and do not affect hormone levels. In regards to prostate cancer, soy food consumption has been associated with reduced risk of prostate cancer in men.
It’s been widely accepted that 2-3 servings a day of soy foods is healthful when paired with a balanced diet. Many of the other studies that show adverse health effects of soy are animal studies based on parrots or rats, who are particularly unsuitable for a raw soy diet as they are fed.
Soy and thyroid disorders: Soy has been found to affect the thyroid gland in people who are hypothyroid or are iodine deficient. Patients who are hypothyroid may not necessarily need to avoid soy foods, but instead may need a higher dosage of thyroid hormone. These individuals should limit soy consumption until the problem is corrected, such as adjusting dosage of thyroid hormone for those who are hypothyroid or increasing iodine intake for those who are iodine deficient.
As with all health care concerns, always be sure to speak to a physician or registered dietitian for individualized recommendations.
Soy and CVD: There is evidence that soy food consumption of 1-2 servings per day can lower “bad” cholesterol in our body (LDL cholesterol), but there is no evidence to suggest that it has effects on other markers of cardiovascular health, such as “good” cholesterol (HDL cholesterol), triglycerides, or blood pressure.
*Soy is a common allergy, so please consult a physician or Registered Dietitian personally if you are having issues with soy products.
Takeaway message: Ultimately, aim to stick to whole food soy products such as edamame, miso, tempeh, tofu, and soy nuts and choose processed soy products, such as soy-based meat alternatives and soy protein isolates less often. Moderate soy food consumption has been shown to have beneficial effects on breast cancer risk, LDL cholesterol, and may be protective against prostate cancer. Soy consumption has not been shown to have detrimental effect on men.
A lot of research regarding soy (and many other topics!) are sensationalized to create a good news story. Always be critical of what you read, hear, or see and try to take matters into your own hands by seeking out good quality, evidence-based research.
For some of my favourite recipes using soy (shown above), check out my Instagram page @tastingtothrive_rd.
I plan to write an entire article dedicated to the best ways to cook tempeh and tofu, so stay tuned!
Applegate CC, Rowles JL, Ranard KM, Jeon S, Erdman JW. Soy Consumption and the Risk of Prostate Cancer in Men: An Updated Systematic Review and Meta-analysis. The FASEB Journal. 2017 Apr 1;31(1 Supplement):790-35.
Marini H, Polito F, Adamo EB, Bitto A, Squadrito F, Benvenga S. Update on genistein and thyroid: an overall message of safety. Frontiers in endocrinology. 2012 Jul 31;3:94.Sacks FM, Lichtenstein A, Van Horn L, Harris W, Kris-Etherton P, Winston M. Soy protein, isoflavones, and cardiovascular health: an American Heart Association Science Advisory for professionals from the Nutrition Committee. Circulation. 2006 Feb 21;113(7):1034-44.
Messina M, Redmond G. Effects of soy protein and soybean isoflavones on thyroid function in healthy adults and hypothyroid patients: a review of the relevant literature. Thyroid. 2006 Mar 1;16(3):249-58.
Messina M, Watanabe S, Setchell KD. Report on the 8th international symposium on the role of soy in health promotion and chronic disease prevention and treatment. The Journal of nutrition. 2009 Apr 1;139(4):796S-802S.
Messina V et al. Vegan for Her. Da Capo Lifelong. 2013.
Messina M. Insights Gained from 20 Years of Soy Research, 2. The Journal of nutrition. 2010 Dec 1;140(12):2289S-95S.
Adams J et al. Never Too Late to Go Vegan. The Experiment. 2014.
Martinez J, Lewi J. An unusual case of gynecomastia associated with soy product consumption. Endocrine Practice. 2008 May 1;14(4):415-8.
Siepmann T, Roofeh J, Kiefer FW, Edelson DG. Hypogonadism and erectile dysfunction associated with soy product consumption. Nutrition. 2011 Jul 1;27(7):859-62.
Hilakivi‐Clarke L, Andrade JE, Helferich W. Is Soy Consumption Good or Bad for the Breast?–3. The Journal of nutrition. 2010 Dec 1;140(12):2326S-34S.
Messina M. Soybean isoflavone exposure does not have feminizing effects on men: a critical examination of the clinical evidence. Fertility and sterility. 2010 May 1;93(7):2095-104.
Dietitians of Canada. Health Benefits of Soy. 2015. https://www.dietitians.ca/Your-Health/Nutrition-A-Z/Soy/Health-Benefits-of-Soy.aspx