Saturday, October 10, 2009

Dietary modifications for prevention of nephrolithiasis

Secondary prevention of nephrolithiasis is often overlooked, but since a large percentage of 1st-time stone formers will go on to develop another episode of nephrolithiasis, it makes sense to make simple dietary modifications that can minimize the risk of this occurring. This is important not only from the perspective of preventing the pain associated with an episode of nephrolithiasis, but also to cut down on the risk of complications associated with nephrolithiasis (e.g., need for a urologic procedure, obstructive renal failure, nephrocalcinosis, etc.)

There are a few dietary measures which have been shown to reduce the risk of nephrolithiasis. Amongst the most important are the following pieces of advice:

1. Drink plenty of water (e.g., maintain a urine output of greater than 2-2.5 Liters a day).
2. Eat a diet low in animal fat.
3. Eat a diet low in sodium.
4. For individuals who form calcium oxalate stones (the most common form of nephrolithiasis in the general population), avoid excess oxalate-rich foods, which include spinach, beets, rhubarb, and (unfortunately) chocolate.

A recent article by Taylor et al in this month's JASN, "DASH-Style Diet Associated with Reduced Risk for Kidney Stones," suggests a similar strategy for kidney stone prevention: using the "DASH" (Dietary Approaches to Stop Hypertension) diet to reduce the risk of nephrolithiasis. In this study, investigators looked at individuals enrolled in several large cohorts (the Health Professionals Follow-Up Study, the Nurse's Health Study I, and the Nurse's Health Study II) and categorized each individual into separate quartiles according to their "DASH" score--that is, how closely each individual adhered to the DASH diet, which is high in fruits and veggies, moderate in animal fat, and low in animal protein. Interestingly, the greater the adherence to the DASH diet, the less the chance of having kidney stone formation. The beneficial effect of the DASH diet even persisted when controlled for hypertension (which is reduced with the DASH diet and also has been epidemiologically linked to nephrolithiasis). This study provides further proof that some of the dietary interventions are indeed effective at preventing stone formation and furthermore provide a dietary framework with specific recommendations that could be suggested to patients eager to prevent further episodes of nephrolithiasis.

Another interesting finding of the study: the highest quartile DASH scorers (which had the lowest risk of kidney stones) also had the highest dietary calcium intake. It's somewhat counterintuitive that calcium-based kidney stones cannot be prevented simply by taking in less calcium, but this and other studies have proven this paradox again and again.

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