Is Soy Protein Isolate Safe?

When soybeans are pressed and the oil is extracted, what's left over is an almost pure form of protein. After a quick wash to remove sugars and fiber, you are left with soy protein isolate. Because it contains all the essential amino acids, soy protein isolate is very important to people who don't eat meat, the only other source of complete protein. Soy protein isolate also contains isoflavones, which are phytoestrogens, or plant chemicals that act like estrogen in the body. Soy isoflavones demonstrate a number of beneficial health effects, but they may be detrimental for some people.

Benefits

As part of a balanced diet, soy may help lower "bad" cholesterol without affecting "good" cholesterol, according to the University of Maryland Medical Center. The isoflavones in soy protein isolate may help reduce menopause symptoms like hot flashes and night sweats, and the investigation into soy protein's positive effect on the preservation of bone density is ongoing as of time of publication. The two aspects of soy protein isolate that are of most concern are its potential in preventing diarrhea in infants and breast cancer in adults. While soy protein isolate has shown promise in these areas, it has also shown some negative effects.

Infants

According to MayoClinic.com, children from 2 to 36 months old may suffer less diarrhea when fed a soy protein isolate formula, although some develop intestinal distress instead. Soy protein isolate formulas are also a nutritious alternative for infants who cannot tolerate cow's milk, but controversy has arisen over the presence of soy isoflavones. Advocacy groups have concerns that these plant chemicals could cause thyroid and reproductive disorders and accelerate the onset of puberty. The long-term effects of feeding soy protein isolate to infants has not been fully studied, but a 2001 study in the "International Journal of Toxicology" found that soy protein isolate caused early puberty in female rats. The researchers didn't believe this would translate to human experience, though, in part because no similar effects have been reported despite the millions of infants receiving soy formula. MayoClinic.com recommends consulting your doctor before using a soy infant formula.

Cancer Risk

The phytoestrogens in soy protein isolate may also have an effect on cancer risk. They may protect men from prostate cancer and women from breast cancer, although the mechanism isn't clear. According to the Penn State College of Agricultural Sciences, soy protein consumption seems to prevent breast cancer when consumed by younger women, but increase the risk in post-menopausal women. Soy isoflavones do cause breast tissue cells to divide, which could increase tumor growth -- MayoClinic.com recommends that people with any type of hormone-sensitive cancer discuss soy protein consumption with their doctors.

Safe Consumption

The safety of soy protein isolate has everything to do with the concentration of soy isoflavones, and it's safest to keep your consumption to under 100 mg per day. Soy protein isolate is lower in isoflavones than other forms of soy, so most people can include it in their diets without a problem. Soy protein isolates are frequently used in imitation meat -- soy hot dogs contain about 15 mg of isoflavones, a soy sausage contains about 4 mg, but a soy burger can contain up to 50 mg. Soy protein isolates are also used in imitation cheese -- soy mozzarella has about 8 mg of isoflavones. Soy protein isolates seem to be safe for healthy adults, but discuss your concerns with your doctor if you are unsure.