Soy Protein (generic name)
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TraditionWARNING: DISCLAIMER: The below uses are based on tradition, scientific theories, or limited research. They often have not been thoroughly tested in humans, and safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider. There may be other proposed uses that are not listed below.
Adults (over 18 years old)
Soy is typically consumed as a protein drink, soy flour, isolated soy protein (e.g. Supro®), extract, fiber/cereal, or milk beverage. Studies have examined the effects of 10-80 grams of soy with an isoflavone content of about 40-120 milligrams taken daily for up to six months by mouth.
A dose of 25-50 grams of soy protein taken daily by mouth has been studied in people with high cholesterol. Isoflavone content has ranged from 60-90 milligrams daily. Cholesterol and low-density lipoprotein levels have been reduced in people using 28 grams daily of soy protein with a high isoflavone content, or with Abacor®, a brand that contains 26 grams of soy protein. There is limited study of soymilk (400 milliliters daily) in pre-menopausal women, with reported benefits on cholesterol levels. Additional doses have been studied but are not recommended due to a lack of available scientific evidence.
Children (under 18 years old)
Due to potential safety concerns, a qualified healthcare provider should be consulted regarding the choice of infant formula.
SafetyDISCLAIMER: Many complementary techniques are practiced by healthcare professionals with formal training, in accordance with the standards of national organizations. However, this is not universally the case, and adverse effects are possible. Due to limited research, in some cases only limited safety information is available.
Soy may act as a food allergen similar to milk, eggs, peanuts, fish, and wheat. Symptoms of an allergic reaction range from a runny nose to a sudden drop in blood pressure.
Side Effects and Warnings
Soy has been a dietary staple in many countries for more than 5,000 years and it does not appear to cause long-term toxicity. Aside from allergic reactions, limited side effects have been reported in infants, children, and adults.
Soy protein taken by mouth has been associated with stomach and intestinal difficulties, such as bloating, nausea, and constipation. More serious intestinal side effects have been uncommonly reported in infants fed soy protein formula, including vomiting, diarrhea, growth failure, and damage/bleeding of the intestine walls. People who experience intestinal irritation (colitis) from cow's milk may also react to soy formula.
Based on human case reports and animal research, soy may affect thyroid hormone levels in infants. There have been rare reports of goiters (enlarged neck due to increased thyroid size). Hormone levels became normal again after stopping soy. Infants fed soy or cow's milk formula may also have higher rates of atopic eczema than infants who are breastfed.
Acute migraine headache has been reported with the use of a soy isoflavone product. Based on animal research, damage to the pancreas may theoretically occur from regularly eating raw soybeans or soy flour/protein powder made from raw, unroasted, or unfermented beans.
The use of soy is often discouraged in patients with hormone-sensitive cancers, such as breast, ovarian, or uterine cancer, due to concerns about possible estrogen-like effects (which theoretically may stimulate tumor growth). Other hormone-sensitive conditions, such as endometriosis, may also theoretically be worsened. In laboratory studies, it is not clear if isoflavones stimulate or block the effects of estrogen or both (acting as a "receptor agonist/antagonist"). Until additional research is available, patients with these conditions should be cautious and speak with a qualified healthcare practitioner before starting use.
It is not known if soy or soy isoflavones share the same side effects as estrogens, such as increased risk of blood clots. Early studies suggest that soy isoflavones, unlike estrogens, do not cause the lining of the uterus (endometrium) to build up.
There has been a case report of vitamin D deficiency rickets in an infant nursed with soybean milk (not specifically designed for infants). Patients should consult their qualified healthcare practitioners for current breastfeeding recommendations and use formulas with adequate nutritional value.
Pregnancy and Breastfeeding
Soy as a part of the regular diet is traditionally considered to be safe during pregnancy and breastfeeding, although scientific research is limited in these areas. The effects of high doses of soy or soy isoflavones in humans are not clear, and therefore are not recommended.
Recent study demonstrates that isoflavones, which may have estrogen-like properties, are transferred through breast milk from mothers to infants. High doses of isoflavones given to pregnant rats have resulted in tumors in female offspring, although this has not been tested in humans.
In one human study, male infants born to women who ingested soymilk or soy products during pregnancy experienced more frequent hypospadias (a birth defect in which the urethral meatus, the opening from which urine passes, is abnormally positioned on the underside of the penis). However, other human and animal studies have examined males or females fed soy formula as infants, and have not found abnormalities in infant growth, head circumference, height, weight, occurrence of puberty, menstruation, or reproductive ability.
Research in children during the first year of life has found that the substitution of soy formula for cow's milk may be associated with significantly lower bone mineral density. Parents considering the use of soy formula should speak with qualified healthcare practitioners to make sure the appropriate vitamins and minerals are provided in the formula.