Nutritional aspects of stone disease

Incidence and prevalence of kidney stones are affected by genetic, environmental, and nutritional factors [1] and have fluctuated markedly over the centuries [2]. Because it appears that peaks of stone disease always occur during periods of affluence, and stone episodes are rare during war and recession [3], several authors [2] have concluded that nephrolithiasis is-at least in part-a nutritional disease. Another hint that nutrition may be an important determinant of stone formation comes from the clinical presentation of stone disease. Whereas large struvite stones (mainly in the bladder) are highly prevalent in developing countries where malnourishment and recurrent infections are common, small upper urinary tract stones, consisting of calcium oxalate or uric acid, usually form in people living in the affluent nations of the western hemisphere [1,4]. Kidney stones can form during a state of urinary supersaturation, the driving force for crystallization. Because urine is regularly supersaturated with respect to various salts, crystal formation is very common in nonstone formers and stone formers alike, and it may even be absent in kidney stone formers [4]. Thus, uncomplicated crystalluria does not distinguish between stone formers and healthy people. Landmark clinical studies by Robertson et a] [5], however, have shown that under identical conditions of dietary and fluid intake, healthy controls almost exclusively excrete single calcium oxalate crystals 3 to 4 mum in diameter, whereas recurrent calcium stone formers pass larger crystals, 10 to 12 mum in diameter, often fused into polycrystalline aggregates 20 to 300 mum in diameter. Thus, those who form stones appear to be more "sensitive" to a given diet than nonstone formers, either because they excrete urines with an abnormal propensity to form large crystal aggregates ("free-particle" theory of stone formation), or because their urinary crystals increasingly attach to urinary epithelia ("fixed-particle" theory of stone formation) in order to grow into full-size stones [4,6]. In any case, it is in these "hypersensitive" subjects that "bad dietary habits" induce nephrolithiasis, making nutritional aspects important [6,7]. This article reviews the current evidence-based knowledge of the impact of nutrition on the "hardest" endpoint in studies on nephrolithiasis, that is, recurrence of a kidney stone.