The Relevance of Phytate for the Treatment of Chronic Kidney Disease

Diets high in plant-based foods are commonly recommended for people with chronic kidney disease (CKD). One putative advantage of these diets is reduced intestinal phosphate absorption. This effect has been ascribed to phytic acid (myoinositol hexaphosphoric acid) and its anion, phytate, that are present in many plant foods, particularly in the seeds, nuts, grains and fruits of plants. This paper reviews the structure and many actions of phytate with particular reference to its potential effects on people with CKD. Phytate binds avidly to and can reduce gastrointestinal absorption of the phosphate anion and many macrominerals and trace elements including iron, zinc, calcium and magnesium. This has led some opinion leaders to label phytate as an "anti-nutrient." The human intestine lacks phytase; hence, phytate is essentially not degraded in the small intestine. A small amount of phytate is absorbed from the small intestine, although phytate bound to phosphate is poorly absorbed. Clinical trials in maintenance hemodialysis patients indicate that intravenously administered phytate may decrease hydroxyapatite formation, vascular calcification and calciphylaxis. Orally administered phytate or in vitro studies indicate that phytate may also reduce osteoporosis, urinary calcium calculi formation and dental plaque formation. Phytate appears to have anti-inflammatory and antioxidant effects, at least partly due to its ability to chelate iron. Other potential therapeutic roles for phytate, not definitively established, include suppression of cancer formation, reduction in cognitive decline that occurs with aging, and amelioration of certain neurodegenerative diseases and several gastrointestinal and metabolic disorders. These latter potential benefits of phytate are supported by cell or animal research or observational studies in humans. Many of the above disorders are particularly common in CKD patients. Definitive clinical trials to identify potential therapeutic benefits of phytate in CKD patients are clearly warranted.