Soy Consumption and Breast Cancer
Breast cancer is one of the most common cancers diagnosed in women worldwide and is the second leading cause of death in women after lung cancer. Breast cancer is strongly linked to ovarian hormones and estrogen levels. Factors such as high endogenous estrogen levels and hormone therapy play a role in increasing the risk of breast cancer Indeed, 2/3 of breast cancer cases are estrogen receptor (ER) positive.
Because soy isoflavones are very similar to estrogen, many health practitioners find that soy will act as an estrogen molecule, and women may say caution against soy consumption in women with breast cancer and postmenopausal women. However, according to some experts, this is wrong. Because soy isoflavones compete with endogenous estrogen to bind receptor sites in the breast. Thus, they can reduce estrogen-induced growth and proliferation in breast tissue and reduce endogenous estrogen concentrations. Indeed, it has been shown that soy isoflavones can act as estrogen antagonists in estrogen-rich environments and as estrogen agonists in low estrogen environments. There is also evidence that the bioavailability of soy isoflavones may be inversely proportional to estrogen levels.
Epidemiological studies have shown that soy isoflavones have a protective effect on breast cancer risk; It shows a 16% risk reduction per 10 mg of isoflavone consumed daily. A study conducted in the Netherlands found that high plasma genistein levels are associated with up to a 32% reduction in breast cancer risk. A 2009 study investigating soybean intake and breast cancer survival found that soy meal consumption was associated with a significant reduction in both the risk of death and breast cancer recurrence.
A 1997 study found that genistein is a potent estrogen agonist and exhibits cell growth inhibitory effects in breast cancer cells in vitro. A more recent study found that genistein works to inhibit topoisomerase II activity, thus resulting in inhibition of breast cancer growth. They investigated the radioprotective effects of genistein by injecting female mice with isoflavone 24 hours before receiving a toxic dose of radiation, and found that genistein-treated mice expressed less DNA damage-responsive and cell cycle checkpoint genes than untreated mice. Magee et al. They investigated the effect of kumestrol, glycine, daidzein, and the metabolites equol and O-desmethylangolensin on MDA-MB-231 cells and found that each inhibited invasion by about 30% at the lowest dose, while genistein and kumestrol were the strongest inhibitors. effects on infestation at the highest dose.
Shike et al. Supplementation of soy isoflavones in women with breast cancer found that soy consumption alters gene expression in breast cancer tumors, particularly FANCC and UGT2A1, both of which are involved in the development of breast cancer tumors. Breast cancer patients had a subset of tumors with upregulated FGFR2 expression, a marker of poor prognosis, and overall soy intake did not significantly alter cell proliferation and apoptosis indices compared to the placebo group. While this may seem discouraging at first, the article points out that the clinical consequences of this small upregulation have yet to be determined.
Another common concern with soy supplementation, especially in postmenopausal women, is that it causes lymphocytopenia, the condition of having low levels of lymphocytes in the blood. Some of these concerns stem from a multicenter study published in 2001 in which postmenopausal women supplemented ipriflavone, a synthetic isoflavone, 600 mg for 3 years. Out of 234 women, 13.2% developed subclinical lymphocytopenia (<0.5 x 10 developed 3 / mm 3). Another 2-year study found that 3% of its participants also developed abnormal lymphocyte counts. Ben-Hurt et al. They found that postmenopausal women also had higher levels of monocytes, indicating that menopause definitely alters hematological parameters.
A rat study by laboratories refutes these results. The study found that not only did ovariectomy increase lymphocyte, monocyte, eosinophil and basophil differential numbers, but also soy isoflavones brought leukocyte counts to pre-operative levels. To test the accuracy of this in human populations, our lab also investigated the extent to which a 1-year 25g soy protein containing 60mg isoflavone supplement altered lymphocyte counts in postmenopausal women. This study showed no effect on total and differential white blood cell counts in postmenopausal women; this may be because the estimated isoflavone content of soy protein is lower than the 60 mg pharmacological dose.
As leukocyte counts tend to rise with menopause, lowering the white blood cell count is not a bad side effect for soy at pharmaceutical doses. Additionally, supplementation of soy protein had no significant effect on leukocyte levels, suggesting that soy supplementation is generally safe for healthy postmenopausal populations.
Soy and Cardiovascular Disease
As mentioned earlier, soy isoflavones are phytoestrogens. Estrogen is known to be cardioprotective, so it makes sense that soy can also be cardioprotective. Most of the clinical studies investigating the impact of soy supplements on heart health mainly focus on cholesterol levels. This may be because phytosterols, such as those found in soy, compete with cholesterol for gut absorption.
A 2015 study investigated the effect of a standard soy milk supplement for 8 weeks on the effect of a soy milk supplement enriched with 2g of phytosterol and 10g / day of inulin. Both groups saw a reduction in LDL-C in both groups, while the study group supplemented with extra phytosterols and inulin achieved significantly better results. TC also decreased significantly in the study group compared to the control of normal soy milk. Soy can be beneficial in many ways beyond soy milk. One study supplementing whole soy foods (3-4 servings per day) for 12 weeks found that the soy intervention significantly lowered total cholesterol, LDL-C, non-HDL cholesterol, and apoB, even if BMI did not decrease.
A previous study also found that soy protein supplementation caused a decrease in cholesterol levels. Prehypertensive women supplementing 40g of soy flour have seen decreases in LDL-C and high-sensitivity C-Reactive Protein (CRP), a marker of inflammation. Interestingly, another study found that 1 month of soybean supplementation moderately reduced arterial stiffness but did not improve inflammatory biomarkers. Additionally, Lucas et al. It has been determined that soy isoflavones prevent both hyperlipidemia and atherosclerotic lesions in ovariectomized Golden Syrian Hamsters.
While there are still gaps in research for CVD and soy consumption, research generally points to a positive effect of soy on heart health regardless of its effect on cholesterol. It is particularly important to find that soy significantly reduces the development of atherosclerotic lesions in a hamster model of postmenopausal CVD, as CVD remains the leading cause of death in the United States.
Author: Ozlem Guvenc Agaoglu