Nutrition Therapy for Kidney Stones

The nutritional plan of care mainly relates to the nature of the stone. The diet is designed to reduce the intake of the nutrients that lead to the formation of particular type of stone.

Calcium Stones

A low-calcium diet of about 400 mg/day is usual." given (Table 21-2) (i.e., about half the average adult intake of 800 mg). This lower level is mainly achieved by removal of milk and dairy products, the main dietary sources of calcium. Other secondary calcium sources are whole grains and leafy vegetables. If a stone is calcium phosphate, additional sources of phosphorus (e.g., meats, legumes, and nuts) should be controlled. If a stone is calcium oxalate, foods high in oxalate (see Box 21-1) should be avoided.
Because calcium stones have an alkaline chemistry, an acid ash diet may also be used to create a urinary environment that is less conducive to precipitating the basic stone elements. The classification of food groups is based on the acidity (pH) of the metabolic ash produced (Box 21-2). An acid ash diet increases the amount of meat, grains, eggs, and cheese and limits the amount of vegetables, fruits, and milk. An alkaline ash diet outlines the opposite use of these foods. The use of cranberry juice has been promoted to assist in acidifying the urine, but the commercially prepared cranberry juices on the market are too dilute to be effective because they only contain about 26% cranberry juice. Therefore an enormous volume of juice is required to achieve any effectiveness as a urinary acidifying agent. Instead, to effect a sustained acidification of urinary pH, most physicians rely on drugs.

Uric Acid Stones

About 4% of the total incidence of renal calculi are uric acid stones. Because uric acid is a metabolic product of purines, a low-purine diet is sometimes recommended. If dietary control of purines is desired, it can easily be achieved by use of a vegetarian diet that eliminates most meat—especially organ meats, concentrated meat extracts, and gravies.

Cystine Stones

Cystine is derived from the essential amino acid methionine, so a low-methionine diet is sometimes used. Because this diet is essentially a low-protein diet and the rare genetic cystinuria condition occurs mainly in children, the treatment of choice is usually a regular diet to support growth. Medical drug therapy is used to control infection or produce a more alkaline urine. natural sodium (e.g., meat and milk) are only used in moderate portions. Box 19-4 provides a general deletion list for moderate sodium restriction. 3. Strict sodium restriction (500 mg)—In addition to the mild and moderate deletions, the natural sodium food sources of meat, milk, and eggs are used in smaller portions. Milk is limited to 2 cups in any form, meat to 5 oz, and eggs to 1 oz. Higher-sodium vegetables are deleted. Box 19-5 provides a general deletion list for strict sodium restriction.