Kidney stones are hardened crystalized deposits that form from an excess of minerals and oxalates that concentrate in the urine, grow, and can block the flow of urine through the kidneys. Symptoms include pain in the lower back or pelvic area and possibly blood in the urine. It is often a hereditary condition and can also be caused by infection or from medications.
Testing the kind of stones passed determines which foods need to be restricted in the diet. Most often the stones are made up of calcium and oxalates. Excessive calcium excretion may be due to a parathyroid abnormality but is more likely caused by an excess of protein in the diet. It is recommended that daily protein intake from meat, chicken, and fish be limited to 7 or 8 ounces.
Oxalates are found in many foods, but according to a study only a few, other than protein, actually raise urinary oxalate levels—spinach, rhubarb, beet greens, chocolate, tea, wheat bran, nuts, almonds, peanuts, and strawberries.
Calcium should not be restricted in the diet; lower calcium intake actually increases the risk of stone formation. Calcium binds with oxalates in the gut and prevents their absorption and consequently leads to the formation of stones. Sodium stimulates excretion of calcium and should be restricted to 2500 mg daily. Caffeine increases calcium excretion. High sugar drinks and citrus juices are risks for stone formation.
Drinking water throughout the day is very important in keeping the mineral content of the urine in dilution; 16 ounces every 4 hours is recommended. A high fiber diet reduces urinary excretion of calcium; however, some individuals do not absorb calcium well and eating too much fiber can result in an overall calcium deficiency.
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