Inability of soy to lower LDL cholesterol

Importantly, we are referring to people with mildly elevated cholesterol blood levels in this study by Australian researchers.

First, the details.

• 91 nonsoy consumers with total cholesterol blood levels greater than 5.5 mmol/L (213 mg/dL) were studied
• Total cholesterol between 200 and 239 mg/dL is considered borderline high risk for heart disease.
• All participants took all diets (crossover design) — 3 diets for 6 weeks each — in random order.
• Soy diet: 24 grams soy protein and 70 to 80 mg soy isoflavones
• Soy + dairy diet: 12 grams soy protein, 12 grams dairy protein, and 70–80 mg soy isoflavones
• Dairy diet: 24 grams dairy protein without isoflavones
• Fasting total cholesterol, LDL (bad) cholesterol, HDL (good) cholesterol, and triglycerides were measured after each diet.
• Participants and researchers were not aware of the treatments given (double-blinded).

And, the results.

• Total cholesterol was significantly 3% lower with the soy diet than with the dairy diet
• Triglycerides were significantly 4% lower with both the soy and soy + dairy diets.
• There were no significant effects on LDL, HDL, or the total cholesterol:HDL cholesterol ratio.
• 30 subjects were determined to be equol producers, and cholesterol levels were not affected by equol production.
• About 30% to 50% of people have intestinal bacteria that make equol — a type of isoflavone produced by bacteria in the intestines.

The bottom line?
The authors concluded, “Regular consumption of foods providing 24 grams soy protein per day from isoflavones had no significant effect on plasma LDL cholesterol in mildly hypercholesterolemic subjects, regardless of equol-producing status.”

An earlier review came to the similar conclusion that reductions in LDL cholesterol by soy isoflavones are greater in people with high cholesterol levels compared to people with normal cholesterol levels.

Historical perspective on the evolving status of soy in western diets can be found here.

8/8/08 16:24 JR