FRIDAY, Aug. 8 (HealthDay News) -- Eating foods with soy protein
has been promoted as a way to lower cholesterol, but a new study
finds it has no significant effect on cholesterol levels.
The findings "do not support the current health claims for soy
protein in a general population," said study author Peter R.C.
Howe, director of the Nutritional Physiology Research Centre at the
Sansom Institute for Health Research at the University of South
Australia in Adelaide.
He's referring to the health claims approved for soy foods in
both the United States and the United Kingdom that link daily
consumption of 25 grams of soy protein to a reduction in heart
disease risk through a lowering of LDL, or "bad," cholesterol.
Howe's team studied 35 men and 58 women, average age 52, who had
mildly high cholesterol levels. He assigned each participant to
rotate through one of three diets for six weeks each. Each diet had
varying amounts of soy protein and isoflavones, substances in soy
that some experts say may have cholesterol-lowering powers.
One diet contributed 24 grams of soy protein and 71 milligrams
of isoflavone equivalents, one had 12 grams of dairy protein and 12
of soy protein, with 76 milligrams of isoflavones. The dairy diet,
which served as the control, had 24 grams of dairy protein without
isoflavones.
Howe's team measured each person's blood cholesterol -- LDL, HDL
and trigylcerides -- at the start of the study and after each
six-week diet.
They found no significant effect of the diets with either 24
grams or 12 grams of soy protein on LDL levels.
In his research, Howe also looked closely at whether a person's
ability to maximize the body's response to soy protein had a better
cholesterol-lowering effect. These people are termed "equol
producers" because of their above-average ability to make equol, a
substance produced in the intestines as a metabolite of a potent
soy isoflavone called daidzen. Equol is thought to inhibit LDL.
When Howe compared the cholesterol-lowering effects of those who
were equol producers with those who were not, he found no
differences.
Howe's study was confined to those with mildly high cholesterol;
he said it may have an effect on those with higher cholesterol
levels. And the soy diets did lower triglycerides, a blood fat, by
4 percent.
The findings were published in the August issue of
The American Journal of Clinical Nutrition.
Even though the study found no effect of the soy protein on LDL
cholesterol, Dr. Frank Sacks, a professor of nutrition at Harvard
School of Public Health, called the research interesting. One facet
he finds especially intriguing, he said, is the finding that equol
producers have no benefit either.
After a series of studies on soy and its effect on cholesterol,
the American Heart Association's Nutrition Committee, of which
Sacks is vice-chairman, reviewed the evidence and issued an
advisory, saying there is "nothing special" about soy or
isoflavones for improving cholesterol and that the heart
association doesn't recommend isoflavone supplements.
However, "there are other benefits to soy foods," Sacks said.
They are healthy due to high levels of polyunsaturated fats, fiber,
vitamins and minerals. But, he added, "forget soy protein for
lowering LDL."
More information
To learn more about LDL cholesterol, visit the
American Heart Association.
