Calcium oxalate kidney stones are the most common type of urinary stone. Although of greatest importance in reducing stone recurrence is an increased fluid intake to maintain adequate urine output, foods high in protein, high in oxalate or low in calcium can all increase levels of urinary oxalate and encourage stone formation, especially if you suffer from intestinal disorders such as inflammatory bowel disease or improper fat absorption as occurs in celiac disease and chronic pancreatitis.
High-Protein Foods
A diet high in foods that derive more than 10 percent of their calories from protein exceeds what is recommended on a low-protein diet and can contribute to the formation of calcium oxalate kidney stones. Though most food groups contain protein-rich foods, animal products such as meat, eggs, fish and dairy are generally low-carbohydrate foods that derive a bulk of their calories, as much as 95 percent in the case of tuna fish, from protein, says Dr. Ed Blonz in "The Nutrition Doctor's A-to-Z Food Counter."
Oxalate Foods
Oxalates are a group of organic acids present in plants and synthesized by animals, including humans. A low oxalate diet limits intake to around 50 mg/d. High oxalate foods have more than 10 mg oxalate per serving and include chocolate milk, soy milk, soy cheese, soy sauce, nuts, wheat products, cereals, berries, figs, citrus fruits, beans, leafy green vegetables, starchier vegetables like potatoes, black tea, dark beer and chocolate. Oxalate restriction is usually not indicated except in intestinal abnormalities or in the setting of low calcium intake.
Low-Calcium Foods
Calcium binds oxalate in the gut and prevents it from entering the blood and making its way into the urine where it can contribute to stone formation. The recommended daily allowance for calcium for adults is 1,000 mg daily. Foods that contain less than 100 mg per serving are poor sources. These include processed foods like bread and cream. Many nutritious foods, such as beans, many fruits and vegetables, are low in calcium. Rather than avoid these foods, include leafy green vegetables, which are high in calcium. Tofu is also a good source.
Excess Vitamin C
Doses of vitamin C in excess of 2 g/d may contribute to the formation of stones, as your body is able to convert vitamin C into oxalate. Diets that contain this level of vitamin C are uncommon. Oranges are noted for their vitamin C content, and yet you would have to consume over 30 medium oranges to approach 2 g vitamin C. Do not worry about obtaining too much vitamin C from whole foods, but avoid excessive supplementation.
References
- "Current Medical Diagnosis and Treatment"; Stephen McPhee et al.; 2009
- "The Nutrition Doctor's A-to-Z Food Counter"; Dr. Ed Blonz; 1999
- UPMC: Low Oxalate Diet
- Arizona Cooperative Extension: Calcium and Calorie Content of Selected Foods
- "The Paradigm Diet"; Adam Dave M.D.; 2010
