Soy and kidney stones: a possible link?

by Mary Calvagna, MS

Each year, more than one million Americans are diagnosed with kidney stones. The National Institutes of Health estimates that 10% of the population will develop a kidney stone at some point in their lives. Severely painful, a kidney stone forms on the walls of the kidney and blocks the urinary system. There are several types, but one of the most common contains oxalate.

It is not clear why some people are more prone to kidney stones than others, but research suggests that high levels of oxalate in the urine and a family history of kidney stones may increase a persons risk. Normally, oxalate is not metabolized by the body and is excreted through the urine. But in some cases, it can bind to calcium in the body and form a kidney stone. Oxalate is a common phytate found in many foods, including spinach, peanut butter, and soy.

A decade ago, few Americans knew of soy and fewer still ate it. But now, soy seems to make the nutritional headlines frequently. Soy is a rich source of healthful, unsaturated oil and protein. In addition, soy is being studied for its possible ability to help lower cholesterol, reduce bone loss, and ease menopausal symptoms, as well as for its role in the development of breast cancer.

The U.S. Food and Drug Administration has even allowed manufacturers of soy-based food products to put a health claim on soy food packages. It states:

Diets low in saturated fat and cholesterol that include 25 grams of soy protein a day may reduce the risk of heart disease.

It seems like soy can do no wrong. But what about the oxalate content? A recent study published in the Journal of Agricultural and Food Chemistry* looked at soy and oxalate, and whether consumption of soy can increase kidney stone risk.

Desktop 3 HTML

If you have a history of kidney stones, the American Dietetic Association recommends that you avoid foods that contain more than 10 mg of oxalate per serving and do not exceed 50 to 60 mg of oxalate per day. All the foods tested in this study surpass these levels.

In light of their findings, the studys authors recommend that any person at risk for kidney stones should avoid the soy foods tested in their study. Before removing any foods from your diet though, talk with your doctor about your concerns.

"Oxalate content of soybean seeds, soyfoods, and other edible legumes," by LK Massey, et al. Journal of Agricultural and Food Chemistry, September 2001.