What are the fiber 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

Calcium-stone formers as a group have a lower intake of dietary fiber than do healthy control populations. Dietary fiber, including oat, wheat, and rice bran, can reduce hypercalciuria and lower intestinal calcium absorption by 20-33%. As much as 24 g of dietary fiber per day may be necessary. Wheat bran, for example, is rich in oxalate, which accounts in part for its ability to bind and absorb free intestinal calcium.

However, although no significant adverse effects from increased dietary fiber have been reported, some potential risks exist. For example, dietary fiber may reduce intestinal magnesium, resulting in a deficit. Patients on a very high-fiber diet should be checked periodically for magnesium deficiency. A magnesium supplement, such as magnesium oxide, can be added if necessary.

Another potential problem is reactive enteric hyperoxaluria. Whenever intestinal calcium is reduced, fewer intestinal oxalate-binding sites are available. This leads to more free intestinal oxalate, which is absorbed more easily than oxalate bound to calcium or other agents. The increased free intestinal oxalate is absorbed and is eventually excreted in the urine, increasing urinary oxalate levels.

Because oxalate is proportionately about 15 times stronger than calcium with regard to stone promotion, limiting oxalate absorption in known stone formers makes sense. The easiest way to accomplish this is to limit dietary oxalate any time that intestinal oxalate-binding sites are reduced (such as when dietary calcium intake is reduced). Dietary oxalate can be lowered by limiting such foods as iced tea, coffee, colas, collard greens, spinach, chocolate, nuts, rhubarb, and green, leafy vegetables. Another approach is to use an alternate oxalate-binding agent, such as an iron supplement.


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