As increasing numbers of dieters turn to soy enzyme protein drinks, a better understanding is needed of the benefits and potential disadvantages of the supplement. Health and nutrition websites advertise the benefits of soy as a cure-all for health concerns such as menopausal symptoms, cancer, heart disease and weight problems. The U.S. Food and Drug Administration say that 25 g of soy protein per day with a low-fat, low-cholesterol diet may reduce heart disease. However, many studies are inconclusive, and controversy reigns about the truth of too much soy in the diet.
Thyroid
There is concern that the consumption of relatively large quantities of soy protein, such as diet drinks and powders containing the isoflavone genistein, may suppress thyroid function in people with an iodine deficiency or hypothyroidism. A 1991 paper by the United Soybean Board, which reviewed studies pertaining to the effects of soy on thyroid health, suggested that soy isoflavone supplements has no adverse effects on thyroid function in healthy adults without iodine deficiencies. People predisposed to goiter and autoimmune disorders, or who consume insufficient iodine, could be a risk factor for goiter from excessive soy consumption.
Cancer
Isoflavones in soy are naturally occurring oestrogen-like compounds, which many believe reduce symptoms of menopause but may be linked to breast cancer. According to Nutra Ingredients, the Federal Institute for Risk Assessment in Germany, BfR, says long-term intake of supplements containing isoflavones could promote the development of cancer and put menopausal women at risk. BfR states that complaints of soy-related adverse side effects included itching, eczema, nausea, dizziness, abdominal pain, skin rash and sweating.
Beneficial effects of soy were reported by Top News U.K., which cited a 2010 study by the Cancer Hospital of Harbin Medical University in China that found consumption of soy-based products had a positive effect on breast cancer. Results of the research concluded a 12.9-percent reduction in the recurrence rate of estrogen and progesterone positive breast cancer in 524 females who had undergone previous surgery for breast cancer.
Cholesterol
Soy protein is associated with changes in serum lipid concentrations and may be of benefit in lowering cholesterol. A 1995 study published in the "American Journal of Clinical Nutrition" found that the consumption of soy protein lowered levels of total cholesterol including LDL, the "bad" cholesterol, without significantly lowering levels of HDL cholesterol.
Memory
According to the Harvard School of Public Health, studies suggest that too much soy could lead to cognitive problems. The reference came from findings that older Japanese women in Hawaii, who ate the traditional soy-based diet, were more likely to have memory problems than those who ate a more Westernized diet.
Nutrient Absorption
Soy products may reduce assimilation of some minerals, including calcium, magnesium, copper, iron and zinc, perhaps because of the anti-nutrient, phytic acid. Other inhibitors in soy may interfere with protein digestion and cause pancreatic disorders, according to Soy Online. The website also states that soy could increase requirements for vitamin B12 and vitamin D.
References
- RDA: CFR - Code of Federal Regulations Title 21
- United Soybean Board: Soy and Health: Conclusions
- Nutra Ingredients: Review Casts Doubt on Isoflavone Supplements; Alex McNally; 2007
- TopNews: Soy Reduces Breast Cancer Reappearance After Menopause
- The "American Journal of Clinical Nutrition": Soy Isoflavones Lower Serum Total and LDL Cholesterol in Humans: A Meta-Analysis of 11 Randomized Controlled Trials; Kyoko Taku et al.; 2007
- Harvard School of Public Health: The Nutrition Source Protein: Moving Closer to Center Stage: Straight Talk about Soy: Memory and Thinking Ability
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