*written by Andrew Akhaphong, Mackenthun's Fine Foods Registered & Licensed Dietitian Updated: 4/2/2022
Image Source: D. Hurst / Alamy
It is understandable that there is concern around soy and soy food products. Over the years there are constant debates about whether soy is good for you, or, is soy bad for you. Whatever your position is on soy and soy food products, the purpose of this article is to review the current scientific, evidenced-based literature on soy and soy food products and their impact on health.
Argument: Soy Phytoestrogens Increases the Risks for Breast Cancer and Other Estrogen-Related Concerns
Image Source: Denver Holistic Medicine
Research has found compounds in soy, called phytoestrogens, mimic the effects of the hormone estrogen. The prefix in phytoestrogen, phyto, means these compounds come from plants. See the above image. We have estradiol, a type of estrogen, and isoflavones; you may be wondering where is the phytoestrogen?
According to multiple studies from Oregon State University, Frontiers of Neuroendocrinology, and Nutrients, phytoestrogens are isoflavones, in addition to, lignans. Estrogen hormones are considered a steroid structure which contains cholesterol molecules. Isoflavones are considered phenolic compounds, meaning, they contain tight strings of single oxygen molecules and loose oxygen-hydrogen molecules with aromatic rings shaped like diamonds containing multiple carbon bonds.
Soy is the highest source of phytoestrogens. In addition, other sources of phytoestrogens include beans, lentils, peas, peanuts, flaxseeds, berries, beer, spinach, seeds, rice, whole wheat products, gluten-free products, and sprouts. Traces of phytoestrogens can be found in cereal, potatoes, other fruits and vegetables, and meat.
Because isoflavones are in so many food sources, it is hard to pinpoint that isoflavones from soy alone is the culprit.
A 2006 study published in the journal of Nutrition and Cancer investigated phytoestrogen consumption and breast cancer prognosis (the forecast of disease progress). The researchers investigated 104 Australian between ages 40 and 80 with invasive breast cancer confirmed by biopsy testing between October 2000 and November 2021. Data was collected using questionnaires and food records with food weight consumed to measure phytoestrogen content. The study has found the following...
The odds of increased progesterone risk was up by 66%.
The odds of being diagnosed with a higher stage of breast cancer decreased by 32%.
The odds of current breast cancer tumors increasing in size greater than 15 millimeters decreased by 37%.
The researchers concluded that women with invasive breast cancer confirmed by biopsy testing had a reduced rate of cancer progression despite the increased levels of progesterone.
Weaknesses of this study however, is the lack of a comparing group of generally health adults to observe risks relating to phytoestrogen consumption and accuracy of truthfulness in answering the questionnaires and weighing the food.
A 2008 study published in The Journal of Steroid Chemistry and Molecular Biology reported the concern for phytoestrogen is that it attaches to receptors for estrogen in the human body due to its similarities in structure; however, phytoestrogen's effects are 10,000 times weaker as the actual hormone itself. Because women who are at risk for breast cancer, or have breast cancer, have higher levels of estrogen, having phytoestrogens attaching to receptors for estrogen reduces the ability for estrogen to be absorbed into the body. Phytoestrogens act as a "stop sign" for specific pathways to slow down the production of estrogen too; thus, the researchers concluded a diet high in phytoestrogens like those from soy foods reduces breast cancer risk and progression into advanced stages of breast cancer.
Argument: Men Who Consume Large Amounts of Soy Will Develop Gynecomastia
Gynecomastia is a condition that causes abnormally large breast tissue in men which can cause swelling, discomfort, embarrassment and body dysmorphia.
It is believed consuming soy and soy food products, given its high levels of phytoestrogens, is one of the leading causes for gynecomastia.
A literature review published in the journal of Fertility and Sterility in 2010 investigated multiple studies whether soy and its phytoestrogens increases the risk for feminine-like traits in men. It is known testosterone, the male hormone, inhibits the risk for developing enlarged breast tissue. In addition, an increase in estrogen increases the risk for prostate cancer and its development into advanced stages.
One study that was reviewed found a high intake of phytoestrogens in men greater than 40 years old with advanced prostate cancer had a higher risk for developing gynecomastia than those in its early stages of prostate cancer. Even if consumption of phytoestrogens decreased or stopped entirely, gynecomastia continued to develop which may be likely due to the fact that higher estrogen levels continue to exist as prostate cancer progressed.
Another study reviewed men older than 40 years of age with early detected prostate cancer with high phytoestrogen consumption had a 20% risk increase in developing gynecomastia, but a lower chance of prostate cancer developing into its advanced stages. Regardless, their estrogen levels remained within the normal ranges while those with advanced prostate cancer had estrogen levels beyond the normal ranges.
Argument: Soy Increases Risk for Thyroid Disorders
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Many research studies on soy phytoestrogens and its impact on thyroid health have been on animals such as mice and monkeys; thus, many laypersons often attribute those findings to be reliable and plausible for humans despite our biology being completely different.
For humans, it is still inconclusive and safe to say phytoestrogens do not increase the risk for thyroid disorders. A 2018 study published in Frontiers in Endocrinology did just that. About 20 male and 24 female participants were selected, 22 participants were given 30 grams of soy protein daily while the remaining 22 participants were given 66 milligrams of phytoestrogens daily. Each group followed these assigned regimens for 8 weeks. All of the participants had early onset hypothyroidism. At the end of the 8-weeks, soy protein and phytoestrogen supplementation did not alter thyroid function or thyroid hormones whatsoever - they remained within normal ranges; although, two (one male and one female) doing the phytoestrogen trial went into active hypothyroidism and was treated with levothyroxine.
For those who developed active hypothyroidism from a high intake of phytoestrogen through supplementation, that was only 4.5% of the population sample studied. Though this study only had a small population sample of 44 participants, further studies are needed to determine the effect of phytoestrogen on thyroid disorders; whether the population sample needs to be larger or need to involve investigating general healthy persons without signs of early onset hypothyroidism.
What Current Research Do Show As Benefits of Soy and Soy Food Products
Improve Cholesterol Levels Current research suggests an average intake of 25 grams of soy protein daily may reduce LDL (bad) cholesterol by 3%. In addition, it is assumed the reduction in LDL cholesterol may even be more if animal protein consumption is lower.
Reduce Heart Disease Risk The arguments of soy phytoestrogens have been shared, but research shows that a diet high in legumes and beans like soy can reduce heart disease risk. The phytoestrogens may reduce inflammation around the heart and the blood vessels which may alleviate blood pressure concerns and stress damage to heart and vessel tissue. A diet rich in soy and soy food products lowered stroke risk by 20% and heart disease by 16%.
Improve Cholesterol Levels Current research suggests an average intake of 25 grams of soy protein daily may reduce LDL (bad) cholesterol by 3%. In addition, it is assumed the reduction in LDL cholesterol may even be more if animal protein consumption is lower.
Reduce Heart Disease Risk The arguments of soy phytoestrogens have been shared, but research shows that a diet high in legumes and beans like soy can reduce heart disease risk. The phytoestrogens may reduce inflammation around the heart and the blood vessels which may alleviate blood pressure concerns and stress damage to heart and vessel tissue. A diet rich in soy and soy food products lowered stroke risk by 20% and heart disease by 16%.