Soy Protein - Health

Health

A meta-analysis concluded soy protein is correlated with significant decreases in serum cholesterol, low density lipoprotein (LDL, bad) cholesterol and triglyceride concentrations. However, high density lipoprotein (HDL, good) cholesterol did not increase. Soy phytoestrogens (isoflavones: genistein and daidzein) adsorbed onto the soy protein were suggested as the agent reducing serum cholesterol levels. On the basis of this research, PTI, in 1998, filed a petition with FDA for a health claim that soy protein may reduce cholesterol and the risk of heart disease.

The FDA granted this health claim for soy: "25 grams of soy protein a day, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease." One serving, (1 cup or 240 mL) of soy milk, for instance, contains 6 or 7 grams of soy protein.

In January 2006, an American Heart Association review of a decade-long study of soy protein benefits cast doubt on the FDA allowed "Heart Healthy" claim for soy protein. The panel also found soy isoflavones do not reduce postmenopause "hot flashes" in women, nor do isoflavones help prevent cancers of the breast, uterus, or prostate. Thus, soy isoflavones in the form of supplements are not recommended. Among the conclusions, the authors state, "In contrast, soy products such as tofu, soy butter, soy nuts, or some soy burgers should be beneficial to cardiovascular and overall health because of their high content of polyunsaturated fats, fiber, vitamins, and minerals and low content of saturated fat. Using these and other soy foods to replace foods high in animal protein that contain saturated fat and cholesterol may confer benefits to cardiovascular health."

In February 2012, the European Food Safety Agency (EFSA) published a scientific opinion on isolated soy proteins and reduction of blood LDL-cholesterol concentrations. The EFSA took into account that only four vs fourteen randomized controlled trials (RCTs) reported an effect of ISP on blood LDL/non-HDL cholesterol concentrations, while the rest shows no effects. The EFSA concludes that a cause and effect relationship has not been established between the consumption of ISP and a reduction in blood LDL-cholesterol concentrations.

Soy is also rich in estrogenic compounds, such as genistein and daidzein; however, research is conflicting as to whether or not it can cause increases in estrogen in males.

A 2007 study by Goodin et al. reported that 56g of soy protein powder per day caused serum testosterone to fall 4% in four weeks in a test group of 12 healthy males. (An error in the abstract said 19%, and this figure was erroneously reported by the media.) ) According to the study, the data supported further studies of these hormonal effects as a mechanism in prostate cancer prevention. However, a study conducted by the Miami Research Associates refutes the finding of the Goodin study, finding soy protein had no significant impact on testosterone levels in healthy males. In fact, only one participant in the Goodin study actually saw a drop in testosterone. The participant in question had testosterone levels 200% higher than all of the other subjects, and during the study, his levels dropped to bring him in line with the other participants. The Goodin study did not conclusively suggest the participant's erratic testosterone levels were related to the soy protein.

Lunasin, a 43 amino acid soy peptide, has been reported to reduce inflammation by reducing interleukin 6, and may help in leukemia.