Previous studies have shown that people who eat significant amounts of soy are less likely to develop heart disease.
But in the past it had been suggested that soy's potency may come from the high amounts of isoflavones. However while these natural compounds have been shown to have benefits for menopause symptoms and other hormone-related conditions, recent research has confirmed that isoflavones do not lower cholesterol.
The new study from researchers at the Jean Mayer USDA Human Nutrition Center on Aging at Tufts University shows that soy protein may lower LDL, also known as the bad cholesterol, a small amount, possibly contributing to decreased risk of heart disease in other ways.
High levels of LDL cholesterol are known to contribute to atherosclerosis, the narrowing and hardening of the arteries, a condition that is related to increased chances of heart attack.
The team looked particularly at the effect of the protein in soy on the particle size of LDL - a larger LDL particle size is associated with lower risk of heart disease. They examined the outcome of soy protein diets, either enriched or depleted of soy isoflavones compared to common sources of animal protein, either with added isoflavones or without.
People who ate diets high in soy protein significantly increased their LDL particle size compared to periods when they were provided with diets high in animal protein, the researchers report in the March edition of the Journal of Nutrition(134:574-57).
The isoflavones did not contribute to either type of protein's effect on LDL particle size.
The potential cardiovascular benefits were seen in women who had a mean soy protein intake of 55 grams a day and men who had a mean soy protein intake of 71 grams a day, an amount that can be obtained from eating soy-based main course each day, they suggest.
Foods containing soy protein can already be marketed in some countries with a heart health claim but new evidence of its effects on cholesterol provides further support for functional foods containing soy and could justify the case for a Europe-wide claim.