What are the protein intake recommendations for the treatment of hypercalciuria?

Updated: Apr 23, 2019
  • Author: Stephen W Leslie, MD, FACS; Chief Editor: Vecihi Batuman, MD, FASN  more...
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Answer

High protein intake has been judged second only to vitamin D ingestion in its ability to increase intestinal calcium absorption. Other effects of a high animal protein diet include an increase in urinary oxalate and uric acid, as well as a reduction in urinary citrate.

Urinary sulfate levels can be used as a general marker of oral animal protein intake. Generally, up to 40 mg of sulfate per day is considered normal, whereas in calcium-stone formers, optimal levels would be below 25-30 mg daily.

The possible link between high animal protein intake and kidney stones has been known since at least 1973. This link was found in epidemiologic studies first in India and then in England, Germany, Austria, Japan, Italy, and, finally, the United States. [44] Known stone formers appear to be more sensitive to the stone-enhancing effects of high–animal protein diets than do non–stone forming control populations.

Animal protein affects urinary calcium mainly through its acid-loading ability. Animal protein is high in purines, which are metabolized to uric acid, contributing to the acid load. Animal protein also increases the body's acid load directly. Methionine and cystine, which contain relatively high levels of sulfur, are more common in animal protein than plant protein. When the sulfur is oxidized to sulfate, additional acid is generated. (Sulfate also can form a soluble complex with calcium in the renal tubules, reducing calcium reabsorption and contributing to hypercalciuria.)

Excess acid needs to be neutralized. This often occurs in the bone, where the extra acid is buffered, releasing calcium from the bony stores. The released calcium eventually contributes to increased urinary calcium. Moreover, acid loading directly inhibits calcium reabsorption in the distal renal tubule, which further exacerbates any hypercalciuria. The extra acid also reduces urinary citrate excretion, by enhancing citrate reabsorption in the proximal renal tubule.

Dietary animal protein reduction

Each 75 g of additional dietary animal protein raises the urinary calcium level by 100 mg/day. In one study, increasing methionine ingestion by just 6 g/day was found to raise the daily urinary calcium excretion by 80 mg. Dietary animal protein intake should be less than 1.7 g/kg of body weight per day.

An intriguing randomized study that compared the stone production rates in about 100 known calcium oxalate stone formers who differed in their dietary protein and fiber intakes found significantly fewer stones in the group with the high-fiber, low–animal protein diet. [45] Of course, the possibility exists that the fiber or just the combination of the high fiber and animal protein restriction was effective.

The first group in the study was instructed just to increase fluid intake, whereas the second group was told to increase fluid intake and consume a high-fiber, low–animal protein diet; both groups were observed for 4.5 years. [45] Additional studies are needed to determine exactly which dietary modifications are most efficacious and to eliminate variables, such as uncontrolled sodium and calcium intake, that might influence the outcome.

Oxalate excretion

An association may also exist between high animal protein ingestion and increased oxalate excretion. For example, the production of glycolate, an oxalate precursor, is strongly linked to animal protein intake. However, although some investigators have found a link between high animal protein intake and increased urinary oxalate, others have not. Further studies are needed to determine the presence and significance of any such correlation.


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