Soy intake is one of the most controversial topics under the umbrella of cancer and cardiovascular health. One of the biggest challenges is that there is conflicting research in both areas (Bolca 2010, Varinska 2015). When reviewing small- and large-scale studies, as well as meta-analysis, on the topic, there are two clear points that scientist agree one:
1) There are several factors that can affect the conclusions we make. Examples of these are the various types of isoflavones, the effect that processing has on these isoflavones, the amount of soy consumed, and one’s life stage when they consume the soy products.
2) More research is needed before we make full claims about whether soy has full protective factors against heart disease and breast cancer, or if it may increase one’s risk at all.
What Does the Research Say?
Soy contains phytochemicals call isoflavones. Some of these, such as genistein, have been proven to have a beneficial effect on reducing one’s risk of estrogen-based breast cancer (Bolca 2010). The protective factor can occur in one of two ways:
1) As an estrogen agonist, meaning that the isoflavone mimics estrogen in the body. In fact, one study found they can build to the point of similar levels we would see in pregnancy.
2) As an estrogen antagonist, meaning that it blocks estrogen receptors.
An interesting observation is that soy consumption in girls’ pre-adolescents may help reduce the risk of breast cancer. This is the time period when dietary factors seem to have the greatest effect on breast health (Messina 2009).
In addition to this, Nachvak et al. (2019), completed a large meta-analysis (review of many studies) and found that “Participants in the highest category of dietary soy isoflavones intake had a 10% lower risk of all-cause mortality compared with those in the lowest category.” This dose response was found in the areas of both cancer and cardiovascular health. Jenkins et al. (2019) found similar findings specifically when reviewing cholesterol levels in individuals regularly consuming soy products.
How Can We Apply the Research Findings?
With more research needed for conclusions to be made, what is our best plan of action when it comes to soy intake?
1) Moderation! This is true in all areas of nutrition and is especially important in controversial areas. Whether soy is protective or potential to increase our risk of certain types of cancers is still somewhat unknown so enjoying soy-containing foods in moderation (1-4 times per month) is a great place to start.
2) Individualize for your conditions. If you have a estrogen sensitive disease or disorder (such as endometriosis or PCOS) or have the “breast cancer gene”, it is likely best to limit soy intake. But again, more research is needed to conclusions in this.
3) Choose less processed soy products such as edamame or soybeans more often, and more processed less often. You can do this by adding edamame to your favourite pasta dish or stir fry and soybeans to your favourite soup or chili.
Disclaimer: Please note that this is not meant to be medical advice and you should see your local dietitian or physician for more individualized information based on your medial history and usual dietary intake.
Bolca S, Urpi-Sarda M, Blondeel P, Roche N, et al. (2010). Disposition of soy isoflavones in normal human breast tissue. Am J Clin Nutr. 91(4):976-84. Epub 2010 Feb 17.
Jenkins DJA, Mejia SB, Chiavaroli, L, Viguiliouk E, et al. (2019). Cumulative Meta-Analysis of the Soy Effect Over Time. J Am Heart Assoc. 8(13):1-9.
Messina M, Hilakivi-Clarke L. (2009) Early intake appears to be the key to the proposed protective effects of soy intake against breast cancer. Nutr Cancer. 61(6):792-8.
Nachvak SM, Moradi S, Anjom-shoae J, Rahmani J, et al. (2019). Soy, Soy Isoflavones, and Protein Intake in Relation to Mortality from All Causes, Cancers, and Cardiovascular Diseases: A Systematic Review and Dose Response. Meta-Analysis of Prospective Cohort Studies. J Acad Nutr Diet 119(9):1483-1518.
Varinska L, Gal P, Mojzisova G, Mirossay L and Jan Mojzis. (2015) Review: Soy and Breast Cancer: Focus on Angiogenesis. Int J Mol Sci.16:11728-11749.