Despite past evidence suggesting that eating soy might only lower cholesterol in those whose bodies are able to convert it to an oestrogens-like compound called equol, a new study hints that soy might benefit a wider range of people.
Canadian researchers found that a diet high in soy isoflavones lowered so-called "bad" cholesterol, or LDL, about equally in people who were considered "equol producers" and in those who weren't. The equol producers, however, maintained their previous levels of "good" HDL cholesterol, while the non-producers' HDL dropped as well.
Cyril Kendall, a nutrition researcher at the University of Toronto in Canada, and his colleagues used three previous studies to test whether the ability to produce equol from soy products was linked to changes in cholesterol.
Cholesterol below 60mg is low
In total, the researchers analysed data on 85 people who participated in one of the three studies. In each of the studies the participants ate between 30 grams and 52 grams of soy foods – such as tofu burgers or hot dogs – every day over four weeks.
Before they started eating the soy, both equol and non-equol producers had LDL cholesterol in the range that would be considered high according to the American Heart Association (AHA). Their HDL cholesterol was also considered low.
For LDL cholesterol, the AHA says a score between 160 milligrams per deciliter (mg/dL) and 189 mg/dL is high, while HDL cholesterol below 60 mg/dL is considered low and not protective against heart disease.
After the study, the 33 equol producers' HDL stayed about the same, while the non-equol producers' dropped from about 48 mg/dL to about 46 mg/dL.
LDL reductions are large
As for their LDL cholesterol, the equol producers' fell from about 169 mg/dL to about 152 mg/dL. The non-equol producers' fell from about 174 mg/dL to about 153 mg/dL.
The LDL reductions are large, the authors write in the American Journal of Clinical Nutrition, although that was likely because one of the three studies looked at weight reduction, and that would influence the results.
A 2006 review by the AHA nutrition committee of 22 randomised trials looking at soy and cholesterol said the LDL reduction they observed was relatively small in given the amount of soy a person would have to eat every day to achieve it.
Soy burger displaces hamburger
"From a practical perspective, unless their background is such that they habitually consume a high level of soy every day...it's unlikely that they'll sustain that change in their diet," said Alice Lichtenstein, an author of the report in the journal Circulation.
Lichtenstein, who was not involved with the new study, said that the benefits come when a person replaces less healthy foods with soy. She said a person should not just think they can sprinkle soy proteins over an ice cream sundae and make it a healthy snack.
Kendall agreed that eating soy helps displace foods that can contribute to heart disease.
"If you're having a soy burger you may be displacing a hamburger," he said. Overall, Kendall said, soy should only be one part of a cholesterol-lowering diet.
(Reuters Health, February 2012)
Soy is a high protein quality plant protein