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.
