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C H A P T E R 2 1 Nutrition for Patients with Kidney Disorders 583

Hypercalciuria: Al-Wahsh, 2011). People who have hyperoxaluria, known as “super absorbers,” can absorb
elevated levels of 50% more oxalate than nonstone formers (Reynolds, 2005). Hyperoxaluria can be caused
calcium in urine. by genetic disorders, chronic bowel inflammation, or a high-oxalate intake. Hyperoxaluria
is more of a risk for stone formation than hypercalciuria (Mendonca et al., 2003).
Megadoses: amounts
at least 10 times People who form calcium oxalate stones are advised to limit their intake of oxalate
greater than the DRI. (Box 21.5). Because megadoses of vitamin C increase both oxalate absorption and oxa-
late synthesis in people prone to calcium oxalate stones, daily doses should be limited to
less than 2000 mg/day (Chai, Liebman, Kynast-Gales, and Massey, 2004).
Calcium. Dietary calcium favorably binds with dietary oxalate in the intestines, forming an
insoluble compound that the body cannot absorb. When calcium intake is low, oxalate ab-
sorption and excretion increase, as does the risk of stone formation (Favus, 2011). A normal
calcium intake consumed throughout the day is recommended to decrease the risk of stone
formation. Optimal calcium intake can be attained while minimizing the risk of kidney stone
formation by consuming dietary calcium and avoiding calcium supplements (Favus, 2011).
Protein. High intakes of animal protein increase urinary excretion of calcium, oxalate, and uric
acid and reduce urinary pH (Seiner, Ebert, Nicolay, and Hesse, 2003). Protein intake in excess
of the RDA is not recommended for people with a history of calcium oxalate kidney stones.
Sodium. A high-sodium intake promotes urinary calcium excretion by decreasing calcium
reabsorption by the kidney (Seiner et al., 2003). Patients with hypercalciuria should limit
their intake of sodium.

Nutrition Therapy

Box 21.5 lists nutrition strategies for decreasing the risk of calcium oxalate kidney stone
formation; none are effective when used alone, yet nutrition therapy is considered the cor-
nerstone in kidney stone management, whether or not medication is needed.

The DASH diet, which is high in fruits and vegetables, moderate in low-fat dairy prod-
ucts, and relatively low in animal protein, may offer a new potential approach to preventing
kidney stones (Taylor, Fung, and Curhan, 2009). A study by Taylor et al. (2009) that exam-
ined the impact of a DASH-style diet on the incidence of kidney stones found that the diet is
associated with a marked decrease in kidney stone risk despite its high-oxalate content. There
may be several different mechanisms by which DASH is protective against kidney stones,
including increasing calcium intake, increasing urinary citrate, or increasing urinary pH. The
study data do not support the common practice of restricting dietary oxalate, particularly if
that means a lower intake of fruits, vegetables, and whole grains.

Box 21.5 NUTRITION RECOMMENDATIONS FOR CALCIUM OXALATE
KIDNEY STONES

■ Drink 3 to 4 quarts of fluid throughout the day, with most in the form of water.
■ Avoid high-oxalate foods: peanuts, tree nuts (such as almonds, cashews, hazelnuts),

soybeans, soy milk, wheat germ and wheat bran (including cereals), spinach, black
tea, instant tea, rhubarb, beets, most dried beans (e.g., black, navy or great northern),
chocolate, and sweet potatoes.
■ Avoid large doses of supplemental vitamin C.
■ Maintain adequate calcium intake (e.g., 3 servings/day) that is spread out over the day.
■ Avoid high intakes of animal protein (e.g., Ͼ6 oz/day) and sodium (e.g., Ͼ2 g/day).

Source: National Kidney Foundation. (2012). Diet and kidney stones. Available at http://www.kidney.org/atoz/
content/diet.cfm. Accessed on 7/11/12.