Soy comes from the legume family and is widely used across cultures. It's a fantastic source of protein, and an easy way for vegans or vegetarians to reach their recommended intakes. However, there are many controversies around soy. Let's sort through the current science on soy.
Soy can come in a variety of different products including soy nuts, tofu, tempeh (which is fermented soybean, which means it has a higher protein content compared to tofu), edamame, miso(a traditional Japanese seasoning/paste made by fermenting soybeans with salt and koji), soy protein isolate, soy-based meat substitutes (TVP), and soy milk. Many vegans/vegetarians opt for soy milk, in comparison to other plant-based milks like almond, oat, or rice milk, because it offers more protein.
Soy, “Male Breast”, and Prostate Cancer
Soy contains phytoestrogens (i.e.: isoflavones), which are plant derived estrogens found in a variety of foods. The phytoestrogens in soy do not appear to have any effect on hormone levels under moderate intake (2-3 servings per day) and they have not been shown to affect sexual development. With regards to prostate health, the consumption of soy foods has actually been associated with a reduction in prostate cancer risk in men.
Soy and Heart Health
There is no current observed change on HDL, triglyceride or blood pressure levels with the consumption of soy. However, evidence does support the role of soy protein in the reduction of certain serum lipids, such as low density lipoprotein (LDL) cholesterol, that is related to CVD. Soy-based foods can be included in a balanced heart-healthy diet to possibly support cardiovascular health.
Soy and GMO
There is no evidence to show that genetically modified foods cause allergies or a resistance to antibiotics. Ultimately, it is your choice. If one is concerned about eating genetically modified foods, they can call companies to see if they use GMO foods, look for "GMO-free" labelling, or buy organic foods. Overall, more research is needed in this field, as it is relatively new.
Soy and Breast Cancer
Soy does not appear to have a cause-and-effect relationship with cancer. However, some epidemiological studies have displayed the potentially protective powers of soy foods against breast cancer. A meta-analysis of 18 epidemiological studies found that soy intake is associated with a small reduction of breast cancer risk. For women who are already diagnosed with breast cancer, or are in remission, soy food consumption is significantly associated with decreased risk of death and recurrence for certain types of breast cancers.
For any nutrition-related topic be critical of your research. A lot of research surrounding soy can be misunderstood and sensationalized in order to create a good story. Be a critical thinker as you read any article. Moderate Intake (2-3 servings) of soy products per day is known to be safe and potentially beneficial. Soy consumption does not have any known effect on hormone levels or sexual development and may even have a protective role in reducing the risk for prostate cancer and recurrence of certain breast cancers. If you want to consume soy, I would highly encourage eating whole food sources of soy (edamame, soy nuts, tempeh, tofu) and less processed products (like protein powders and soy-based meat substitutes) less often. Additionally, just like gluten, shellfish, and dairy, soy is a common allergen. So if you are sensitive to soy, avoid it. Overall, while soy may have some potentially positive benefits and play a role in a heart-healthy diet, it is not the silver bullet against any condition. Take a holistic, personalized approach in assessing your needs with your doctor.
Future Research Considerations
· More research is needed on soy with regards to other cancers, especially since many studies are done in Asian populations, compared to Western.
· Even though phytoestrogens may have an anti-estrogenic effect by blocking the more active human estrogen from reaching it’s receptors, I have once read that phytoestrogens may interact with estrogen receptors, on the surface of human cells, giving them the potential to exert mild estrogenic effects. More research needs to be done here, since the evidence seems to be mixed.
1. Meta-analysis of soy intake and breast cancer risk - https://www.ncbi.nlm.nih.gov/pubmed/16595782
2. Soy and its isoflavones: the truth behind the science in breast cancer - https://www.ncbi.nlm.nih.gov/pubmed/23919747
3. Soy protein reduces serum LDL cholesterol and the LDL cholesterol:HDL cholesterol and apolipoprotein B:apolipoprotein A-I ratios in adults with type 2 diabetes - https://www.ncbi.nlm.nih.gov/pubmed/19605528
4. Pros and cons of phytoestrogens - ncbi.nlm.nih.gov/pmc/articles/PMC3074428/
5. Soy consumption and prostate cancer risk in men: a revisit of a meta-analysis - https://www.ncbi.nlm.nih.gov/pubmed/19211820
6. Soy, a complete protein - https://www.ncbi.nlm.nih.gov/pubmed/19145965
7. Soy food intake and breast cancer survival - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2874068/
8. Nutritional and health benefits of soy protein - https://www.ncbi.nlm.nih.gov/pubmed/11312815
9. Soy protein, isoflavones, and heart health - https://www.ahajournals.org/doi/full/10.1161/circulationaha.106.171052
10. GMO, allergies, and soybeans - https://www.ncbi.nlm.nih.gov/pubmed/12709477