Epidemiological investigations suggest that soy consumption may be associated with a lower incidence of certain
chronic diseases. Clinical studies also show that ingestion of
soy proteins reduces the risk factors for cardiovascular disease. This led to the approval of the food-labeling health claim for
soy proteins in the prevention of
coronary heart disease by the U.S. FDA in 1999. Similar health petitions for
soy proteins have also been approved thereafter in the United Kingdom, Brazil, South Africa, the Philippines, Indonesia, Korea, and Malaysia. However, the purported health benefits are quite variable in different studies. The Nutrition Committee of the American Heart Association has assessed 22 randomized trials conducted since 1999 and found that isolated
soy protein with
isoflavones (ISF) slightly decreased
LDL cholesterol but had no effect on
HDL cholesterol,
triglycerides,
lipoprotein(a), or blood pressure. The other effects of soy consumption were not evident. Although the contributing factors to these discrepancies are not fully understood, the source of soybeans and processing procedures of the
protein or ISF are believed to be important because of their effects on the content and intactness of certain bioactive
protein subunits. Some studies have documented potential safety concerns on increased consumption of soy products. Impacts of soy products on thyroid and reproductive functions as well as on certain types of
carcinogenesis require further study in this context. Overall, existing data are inconsistent or inadequate in supporting most of the suggested health benefits of consuming
soy protein or ISF.