US scientists discovered a link between renal calculi and soybeans. Soy, a natural source of fibre and protein that is often used as a meat substitute, is also high in oxalate. This compound can bind to calcium in the kidney, leading to stone formation.

Dr Linda Massey and colleagues at Washington State University in Spokane measured nearly a dozen varieties of soybeans and 13 types of soy-based foods for oxalate. The team found enough oxalate in each of the products tested to potentially cause problems for people with a history of renal calculi. Some of the foods tested contained up to 50 times more than the suggested limit of 10mg/serving recommended for susceptible patients.

The soy-based foods included tofu, soy cheese and soy drinks. The highest levels were found in textured soy protein, which contained up to 638mg/serving. In comparison, spinach, which is also known to be a high source of oxalate, contained about 543mg/serving.

"Under these guidelines, no soybean or soy-based food tested could be recommended for consumption by patients with a personal history of kidney stones," said Dr Massey, but added that individuals with a low probability of kidney stones were unlikely to be affected by the oxalate in soy-based foods.

Oxalate has no nutritional value and cannot be metabolised. It is excreted only through urine and can bond to calcium inside the kidney.

Dr Massey said that further research was needed to find types of soybeans with less oxalate, or to develop a processing method to remove the compound before it reaches consumers.

Source: Washington State University, US

From Health-news.co.uk