Q. Should I avoid eating spinach because it has oxalate found in kidney stones? I already have some kidney stones.
A. Leanne Stephens, a dietetic intern at Tufts' Frances Stern Nutrition Center, responds: "Before making major dietary changes or exclusions, talk to your doctor to find out exactly what kind of kidney stone you had. In America, the most common (about 75%) are calcium oxalate stones, caused by increased calcium and oxalate in the urine. The increased oxalate levels may be impacted by dietary intake, but could be caused by a build-up of oxalate produced naturally in your body.
"Treatment of kidney stones is unique to each individual, so consult your physician and a registered dietitian for a specialized treatment plan. In general, there is a recommendation for increased fluid intake of at least two to three liters per day, equal to 8½ to 12½ cups of water. This will help dilute your urine and flush out any precipitates that may lead to kidney stones. If your health care team decides that a reduction in food oxalate sources will prevent future kidney stone development, they may ask you to avoid certain foods and adjust your intake of other foods or supplements. Foods high in oxalate include spinach, rhubarb, star fruit, beets, tea, chocolate, nuts, wheat and legumes.
"Studies have found that boiling may reduce oxalate levels in spinach and other oxalate-containing foods, so you may still be able to enjoy spinach in small amounts. Additionally, calcium can bind oxalate in the intestinal tract and prevent its absorption, so drinking a glass of milk with your meals may also lower the amount of oxalate your body absorbs. Individuals who consume the RDA for calcium (1,000-1,200 milligrams/day) have a lower risk for kidney stone formation, so you may be asked to increase your dairy consumption or take a calcium supplement. High salt and meat intake have also been associated with development of kidney stones."