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BONN, GERMANY. Kidney stones affect up to 10 per cent of adults in developed countries at some point in
their lifetime. They develop in the urinary system, usually due to an increase in dissolved solids in the urine.
Crystals begin to stick together and slowly form a stone which may grow for months or years before it
causes symptoms. Nutrition is widely believed to play a role in calcium oxalate stones, the most common
type of kidney stone. Earlier studies have focused on individual dietary constituents, so researchers from the
University of Bonn undertook a study of a specially-designed diet to prevent recurrence in patients with
previous calcium oxalate stones.
They recruited 107 men and women and compared their urine composition while on their normal diet and
after a week spent on a diet incorporating food advised for the prevention of stone recurrence. This
consisted of increased intake of water (to 2.5 liters per day), fiber, potassium and vitamin B6, and a
decreased intake of protein, sodium, fat and cholesterol, and no alcohol. Results showed high levels of
metabolic abnormalities linked to stone formation on their normal diets, but a significant reduction on the
study diet. This manifested through an increase in volume of urine, increased pH (reduced acidity) and
increased levels of citrate, a key inhibitor of stone formation. Calcium and uric acid levels in the urine were
reduced on the stone-preventing diet. Analysis of the participants' usual diet identified low fluid intake,
excretion of less than two liters of urine per day, and increased intake of protein and alcohol as the most
important risk factors. These have also been highlighted in previous studies. The shift to a nutritionally
balanced diet according to the recommendations for kidney stone formers reduced the risk of further stones
by 42 per cent, the researchers conclude.
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