Too much soy could lead to kidney stones

NEW RESEARCH indicates that soybeans and soy-based foods, a staple in the diets of many health-conscious consumers, may promote kidney stones in those prone to the painful condition. The finding was published in the Journal of Agricultural and Food Chemistry.

The researchers measured nearly a dozen varieties of soybeans for oxalate, a compound that can bind with calcium in the kidney to form kidney stones.

They also tested 13 types of soy-based foods, finding enough oxalate in each to potentially cause problems for people with a history of kidney stones, according to Linda Massey, at Washington State University in Spokane.

The researchers are the first to identify oxalate in store-bought products like tofu, soy cheese and soy drinks.

Other foods, such as spinach and rhubarb, also contain significant oxalate levels, but are not consumed for their presumed health benefits, Massey said. During their testing, the researchers found the highest oxalate levels in textured soy protein, which contains up to 638 mg of oxalate per 85-gram serving.

Soy cheese had the lowest oxalate content, at 16 mg per serving. Spinach, measured during previous research, has approximately 543 mg per one-cup (2 oz. fresh) serving. Soy, a natural source of protein, fibre and healthy oils, is used to enhance a myriad of foods, ranging from hamburgers to ice cream.

It can be ground into flour and used in a variety of grain products, or formed into chunks and ground like meat.

It is also being studied for its potential to lower cholesterol, reduce bone loss and prevent breast cancer. Oxalate, however, cannot be metabolised by the body and is excreted only through urine, Massey said.

The compound has no nutritional value, but binds to calcium to form a mass (kidney stones) that can block the urinary system, she said.

Further research is needed to find types of soybeans with less oxalate, or to develop a processing method to remove the compound before it reaches consumers, she added.

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