The effects of soy foods and supplements on human health remains a controversial issue. Studies have found inconsistencies in soy health benefits and raised its potential safety concerns .
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Soy Protein and Isoflavones (ISF)
Soy protein contains all essential amino acids. Hence, it is similar to animal sources in protein quality but with less saturated fat and no cholesterol.
Soy isoflavones (ISF) are the primary phytoestrogens in soy. There are 3 main soy ISF: genistein, daidzein and glycitein. Soy ISF have similar structure to 17-beta estradiol, ie. the estrogen hormone in humans, and therefore bind to estrogen receptors. They may have antiestrogenic or estrogen-like effects, depending on various factors.
Genistein has been shown to inhibit the carcinogenesis.
Purported Health Benefits of Soy
1. Prevention of Heart Disease
Soy protein with ISF may lower LDL cholesterol in hypercholesterolemic people, thereby reducing the risk of heart disease.
2. Prevention of Prostate Cancer
Epidemiological studies suggest that consumption of soy foods is associated with a reduction in prostate cancer risk in men (especially Asian population).
However, the results from limited human clinical studies on soy consumption and prostate cancer risk are inconsistent.
Prostate-specific antigen (PSA) is a protein produced by prostate cells. A PSA test measures the amount of PSA in the blood, and is used to screen for prostate cancer and follow prostate cancer patients after treatment. A high PSA level is linked to an increased risk of prostate cancer.
In prostate cancer patients, some studies showed soy protein or ISF reduced PSA concentrations. However, soy protein isolate or ISF did not alter PSA in healthy middle aged men or men with elevated PSA.
Further clinical trials are needed to fully justify the use of soy ISF for cancer prevention and therapy.
3. Prevention of Breast Cancer
Evidence from epidemiological studies suggest that high soy intakes in adolescence are associated with low risk for breast cancer in adulthood.
4. Prevention of Osteoporosis
Numerous studies have examined the relationship between soy foods, soy protein, or isoflavone extracts and markers of bone health and osteoporosis prevention.
Some studies showed a dietary soy intake may have a protective effect on preserving total BMD (especially among Asian women) while others showed no significant benefit of soy foods.
The conflicting results are not enough to warrant the recommendation of soy foods and soy isoflavones for prevention and treatment of postmenopausal osteoporosis. Moreover, the long-term safety of soy isoflavone supplements remains to be demonstrated.
5. Relief of Menopausal Symptoms
There may be beneficial effect of soy isoflavones on hot flush frequency or severity. However, studies show no consistent evidence to support the efficacy of soy isoflavones for menopausal symptom relief.
Potential Health Risks of Soy
1. Increased Risk of Breast Cancer
Results from clinical studies are inconclusive where soy concentrates or ISF (instead of whole soy foods) are generally used. Breast cancer is strongly associated with exposure to high levels of estrogens (ovarian and adipose derived) and estrogenic compounds (diet, environment, etc). Since soy ISF can act as estrogen, there are concerns that exposure to ISF may increase breast cancer risk. Some studies indicate that soy protein isolate increased cell proliferation in the breasts of premenopausal women.
2. Male Hormonal and Fertility Problems
Due to the lack of human studies, the effects of soy on male reproductive health is unknown.
Soy products can interfere with thyroid function, resulting in hypothyroidism or goiter. There are concerns that people with certain conditions such as subclinical hypothyroidism, predisposition to goiter, hypothyroidism and iodine deficiency may be adversely affected by soy products. Infants with congenital hypothyroidism should avoid soy products (such as soy-based formulas) unless necessary.
4. Adverse Effects of Antinutrients
Soybeans contain antinutrients such as protease inhibitors, lectins and phytic acid. Protease inhibitors increase the risk of pancreatic hypertrophy and hyperplasia, thereby inhibiting growth. Lectins interfere with absorption of nutrients. Phytic acid reduces the availability of minerals such as calcium, magnesium, zinc and iron.
5. Harmful By-Products of Soy Processing
Soy protein isolates subjected to alkaline treatment can result in the degradation of natural amino acids and formation of unnatural amino acids such as lysinoalanine (LAL). LAL was shown to be nephrotoxic (toxic on kidney cells) to rats when they were fed diets with high levels of alkali modified soy protein isolate. There are concerns that LAL may pose a health hazard to humans.
How to Safely Consume Soy
If you are allergic or sensitive to soy, avoid it completely.
Otherwise, you can still enjoy soy as part of a healthy diet if you follow these tips…
1. Choose minimally processed soyfoods (preferably fermented) over highly processed soy products (such as soy burger, soy protein, soy cheese, soy ice cream, soy yogurt, soy nuts, soy bean oil, etc)
2. Organic, non-GMO soy is superior to GMO soy. The United States is the top producer of soybeans. More than 90% of soybeans grown there are genetically modified. The genetic modification of soybeans (also known as Roundup Ready soybeans) enables the plants to survive when sprayed with toxic herbicide, Roundup. It’s no wonder that genetically modified soybeans are loaded with pesticides!
3. Fermented soy products such as miso, natto, tempeh, shoyu and tamari are more nutritious and healthier than unfermented soy. The fermentation process removes most of the antinutrients in soybeans and increases nutrients.
4. Do not consume soy as a staple food. Instead, eat it in small portions (such as condiment or side dish) as part of a meal.
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Wha type(s) of soy foods or products that you consume?
Have you experienced health benefits or issues from your soy intake?
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