Soy May Improve Kidney and Heart Disease

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Teixeira SR, Tappenden KA, Carson L, et al.: Isolated soy protein consumption reduces urinary albumin excretion and improves the serum lipid profile in men with type 2 diabetes mellitus and nephropathy. J Nutr 134:1874–1880, 2004.

What is the problem and what is known about it so far?

When people are diagnosed with type 2 diabetes, they often have albuminuria. This means that their bodies are releasing more than normal amounts of a protein called albumin in their urine. This is caused by changes in the kidneys from diabetes. Finding ways to reduce the amount of albumin in the urine is important.

Researchers wanted to know if people who ate isolated soy protein had lower albumin levels in the urine and fats in the blood. Isolated soy protein can be found in soy milk, soy protein powders and tofu.

Who was studied?

Thirty-four men with type 2 diabetes between the ages of 63 and 73 were studied. Men not taking medications or who had no other conditions that changed albumin levels were included. All the men had been diagnosed with type 2 diabetes for at least 5 years.

How was the study done?

The men were put into three groups, which were studied for seven months. Each group ate two different diets at different times. The men ate isolated soy protein during one phase and ate casein (a protein from milk) during the other. (Isolated soy protein and casein can be mixed into foods and drinks.)

The men visited a dietitian every 2 weeks, when their weight and blood pressure was measured.

The men also wrote down what they ate and drank for three days.

Researchers took fasting blood and urine samples six times during the study. Fasting blood samples are taken before a person eats.

What did the researchers find?

The researchers found that isolated soy protein reduced albumin in the urine more than casein did. It also helped increase HDL (the "good" cholesterol). No real difference was noted in LDL (the "bad" cholesterol) levels of the men.

What were the limitations of the study?

Some men dropped out of the study because the isolated soy protein or the casein upset their stomachs.

What are the implications of the study?

Isolated soy protein could help prevent kidney and heart disease. This is especially important in patients with type 2 diabetes because they have a higher risk of getting kidney and heart disease.