All About Soy: Is it Good for You?
Written by: Helayne Speroni on behalf of Supriya Lal, RD
What is Soy?
Soy is a legume originating from East Asia. Legumes include lentils, beans, and peas. They are the edible seeds and fruits coming from the pea family.
Soy can be found in many foods including: tempeh, edamame, tofu, soy nuts, natto, miso among other soy products.
What are the Benefits of Soy?
A Plant Protein:
Soy is a unique plant-based protein in that it contains all of the essential amino acids. These nine amino acids are considered essential because they must be supplied by the diet. Other sources of plant-based proteins contain some of the essential amino acids, but not all of them. All nine essential amino acids are needed in order to maintain metabolic health, bone health and muscle health.
Legume consumption is associated with reduced risk of heart disease. One study found soy consumption to reduce LDL cholesterol (the bad cholesterol). In addition to this, HDL cholesterol (the good cholesterol) levels increased. These effects were more prominent in patients who already had high cholesterol levels in comparison to healthy individuals.¹
Soy is a phytoestrogen which means it functions like estrogen. Estrogen is a hormone that aids in calcium deposition in the bone, thus it is important in maintaining bone health. This is especially important in postmenopausal women as estrogen is not produced as efficiently. Decreased estrogen production in women is associated with decreased bone mass. Decreased bone mass increases risk of fractures. It is estimated that postmenopausal bone loss is about 2% within the first six years.² After the first six years, there is a consistent 0.5-1% loss in bone mass each year.² About 40-50% of postmenopausal women will experience some type of fracture in their later years.² The phytoestrogen benefits of soy have been shown to decrease postmenopausal bone loss.
Soy is rich in protein, fiber, B vitamins, potassium, calcium and provides unsaturated fatty acids among other nutrients. All of these nutrients are important in maintaining proper body functioning.³
Controversies Surrounding Soy: Breast Cancer and Men’s Health
Soy and Breast Cancer:
The benefits of soy consumption on breast cancer risk are undeveloped and conclusions cannot be made at this time. However, consumption of soy-based foods does not increase breast cancer risk. Some evidence does suggest that individuals who grew up eating soy based products at a young age have a decreased risk in breast cancer; however, more research is needed.⁴
Soy and Men's Health:
Misinformation surrounding soy has unfavorably linked soy consumption to erectile dysfunction, infertility and breast development in men. This is proposed to be an effect of the phytoestrogen properties of soy. Upon researching this topic in the pubmed database, studies are flawed and provide no legitimate evidence to support this claim.
One case study that drew a lot of attention to this area of research involved a 19 year old male with diabetes who consumed an enormous amount of soy products. This individual's daily intake of soy led to an isoflavone intake of 360 mg.⁵
Isoflavones are a nutrient naturally found in some plant foods. Isoflavones are responsible for many of the beneficial properties in soy. However, too much of a good thing is not always beneficial.
Moderate intake of soy-based products is considered two portions of soy-based food products per day. To put this in perspective, one serving of boiled soybeans contains 47 mg of isoflavones.⁶ This individual was consuming a high level of isoflavones, surpassing what most healthy Americans would consume in a typical diet.
In addition to this, this individual has type 1 diabetes, which is a risk factor for developing erectile dysfunction.⁷ For these reasons, this case study does not effectively link soy food products with negative effects to men's health.
However, evidence does support the role of soy isoflavones in reducing risk of prostate cancer, the second most diagnosed cancer in men. Soy isoflavones have been shown to stop
prostate cancer growth and development, thus benefiting men’s health over all.⁸
Soy can be a part of a healthy diet for both men and women. It offers nutritional benefits that go beyond just providing energy.
Becerra-Tomás N, Papandreou C, Salas-Salvadó J. Legume consumption and cardiometabolic health. Adv Nutr. 2019;20(4):S437-S450. https://doi.org/10.1093/advances/nmz003.
Agostini D, Zeppa SD, Lecertini F. Muscle and Bone Health in Postmenopausal Women: Role of Protein and Vitamin D Supplementation Combined with Exercise Training. Nutrients.2018;10(8):1103.
Soy beans, mature seeds, raw. U.S Department of Agriculture; agriculture research services. Published April 2018 Accessed September 30, 2020 https://fdc.nal.usda.gov/fdc-app.html#/food-details/174270/nutrients.
Messina M. Impact of soy foods on the development of breast cancer and the prognosis of breast cancer patients. Forsch Komplementmed. 2016;23:75-80 DOI: 10.1159/000444735.
Siepmann T, Roofeh J, Kiefer FW, Edelson DG. Hypogonadism and erectile dysfunction associated with soy product consumption. Nutr. 2011;27(7-8):859-62 doi: 10.1016/j.nut.2010.10.018.
Academy of Nutrition and Dietetics. Recommendation summary; soy foods and their protein and isoflavone content. Accessed September 30, 2020 https://www.andeal.org/template.cfm?template=food_tables&key=300&fbclid=IwAR1fEIkPff3wiQ5MF3HRl74uevby4mhjiGiWpONaUpFvNv6VZE8KhN7y_Ag.
Mayo Clinic. Erectile dysfunction and diabetes:take control today. Published January, 2018. Accessed September 30, 2020 https://www.mayoclinic.org/diseases-conditions/erectile-dysfunction/in-depth/erectile-dysfunction/art-20043927.
HApplegate CC, Rowles JL, Ranard KM, Jeon S, Erdman JW. Soy Consumption and the Risk of Prostate Cancer: An Updated Systematic Review and Meta-Analysis Nutrients. 2018;10(1): 40; https://doi.org/10.3390/nu10010040.