The first human study on the cholesterol-lowering effect of soy protein was reported in 1967 and demonstrated that replacement of mixed proteins by mainly isolated soy protein products at an intake of 100 g/d reduced mean cholesterol levels by >2.59 mmol/L in hypercholesterolemic men. However, health professionals did not pay particular attention to this benefit until a meta-analysis was published in 1995. Anderson et al. analyzed 38 controlled clinical studies published between 1977 and 1994. Among them, 30 studies were conducted with hypercholesterolemic subjects. The results suggested that mean intakes of 47 g/d, ranging from 17 to 124 g, of isolated or textured soy protein resulted in significant reduction in total cholesterol by 9.3%, LDL-cholesterol by 12.9%, and triglycerides by 10.5%, with an insignificant change in HDL-cholesterol levels, compared with animal protein.
The U.S. FDA approved a food-labeling health claim for soy protein in the prevention of coronary heart disease in 1999 but clearly indicated that “the evidence did not support a significant role for soy ISF in cholesterol-lowering effects of soy protein”. Since then, retail soy consumption has significantly increased. Sales of U.S. soy foods doubled in 6 y, from $2 billion in 1999 to $4.3 billion in 2005. Within the last 10 y, the number of soy products has also increased from hundreds to 3000. From 2000–2007, food manufacturers in the United States have introduced over 2700 new foods with soy as an ingredient, including 479 new products introduced in 2006 alone. This has led to extensive research on the beneficial and potential adverse effects of soy intake.
The Nutrition Committee of the American Heart Association has assessed 22 randomized trials published since 1999. Among them, 19 studies were conducted with hyperlipidemic subjects. Results show that mean consumption of 50 g/d, ranging from ∼25 to 133 g, of isolated soy protein containing ISF lowered LDL cholesterol levels by 3% in comparison with milk or other proteins. However, no significant effects on circulatory levels of HDL cholesterol, triglycerides, lipoprotein(a), or blood pressure have been found. Among a subgroup of 19 studies, the mean effects of soy ISF on LDL cholesterol and other lipid risk factors were insignificant. A recent study in postmenopausal women showed that daily supplementation of 25 g of soy protein and 101 mg of aglycone ISF lowered LDL cholesterol and apolipoprotein B levels by 11% and 8%, respectively, and reduced systolic and diastolic blood pressure by 9.9% and 6.8%, respectively, in hypertensive women.