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A More Focused Approach to Phosphorus Nutrition Education for the Adolescent Kidney Patient

      Dietitians are accustomed to providing low-phosphorus nutrition education as a primary focus of kidney nutrition instruction for patients with chronic kidney disease. This is based on heavily researched evidence that excessive phosphorus intake leads to bone mineral disease and increased risk for cardiovascular disease in this population. Coronary-artery calcification is common and progressive in young adults with end-stage renal disease who are undergoing dialysis and occurs much earlier in adolescent patients than in the general population.
      • Goodman W.G.
      • Goldin J.
      • Kuizon B.D.
      • et al.
      Coronary-artery calcification in young adults with end-stage renal disease who are undergoing dialysis.
      As the phosphorus content of the US food supply continues to increase, this issue is growing more complex. Food manufacturers continue to find new ways to improve taste, speed of preparation, shelf life, or convenience of products through the addition of phosphate ingredients.
      • Calvo M.
      • Moshfegh A.
      • Tucker K.
      Assessing the health impact of phosphorus in the food supply: issues and considerations.
      In addition, the growth in availability and intake of convenience and fast foods is contributing to increased intake of phosphorus by those individuals consuming more of these foods, essentially without their knowledge or understanding, as food labels are not required to list phosphorus content.
      • Calvo M.
      • Moshfegh A.
      • Tucker K.
      Assessing the health impact of phosphorus in the food supply: issues and considerations.
      While 2 decades ago, phosphorus additives contributed around 500 mg/day of phosphorus to the American diet, today additives may contribute as much as 1,000 mg/day to the average American diet. This nearly meets the recommended daily allowance (RDA) of 1,250 mg/day for children 9-18 years old and far exceeds the RDA of 500 mg/day for children 1-8 years old.
      • Kalantar-Zadeh K.
      • Gutekunst L.
      • Mehrotra R.
      • et al.
      Understanding sources of dietary phosphorus in the treatment of patients with chronic kidney disease.
      This certainly presents major challenges to young kidney patients instructed to follow a low-phosphorus diet.
      While nutrition education typically focuses on helping adolescent patients reduce the absolute amount of dietary phosphorus, it is becoming more important for dietitians to distinguish between types of phosphorus in the food supply, natural or added, as well as the origin which is animal or plant-based. The two main sources of dietary phosphorus are organic, including animal and plant-based proteins, and inorganic, mostly food preservatives.
      • Chang A.R.
      • Lazo M.
      • Appel L.J.
      • Gutierrez M.
      • Grams M.E.
      High dietary phosphorus intake is associated with all-cause mortality: results from NHANES III.
      These types vary in absorption by the gastrointestinal tract. Typically, phosphorus from organic animal sources is about 40-60% absorbed, while the bioavailability of phosphorus from plant sources is lower, usually <50%.
      • Kalantar-Zadeh K.
      • Gutekunst L.
      • Mehrotra R.
      • et al.
      Understanding sources of dietary phosphorus in the treatment of patients with chronic kidney disease.
      This is due to plant phosphorus being mostly in the form of phytic acid, or phytate, which requires an enzyme for degradation that humans do not express: phytase. Inorganic phosphorus, such as additives, are not protein bound; they are salts that more readily disassociate and are easily absorbed in the intestinal tract.
      • Kalantar-Zadeh K.
      • Gutekunst L.
      • Mehrotra R.
      • et al.
      Understanding sources of dietary phosphorus in the treatment of patients with chronic kidney disease.
      Since inorganic phosphate additives are more bioavailable (above 90%) than organic sources of phosphorus, it is plausible that dietary phosphorus from inorganic sources could have a greater effect on serum phosphorus, FGF-23, and parathyroid hormone.
      • Chang A.R.
      • Lazo M.
      • Appel L.J.
      • Gutierrez M.
      • Grams M.E.
      High dietary phosphorus intake is associated with all-cause mortality: results from NHANES III.
      Another consideration for nephrology dietitians providing low-phosphorus nutrition education is that proteins are rich in phosphorus, with 1 g of protein having 13-15 mg of phosphorus.
      • Gonzalez-Parra E.
      • Gracia-Iguacel C.
      • Egido J.
      • Ortiz A.
      Phosphorus and nutrition in chronic kidney disease.
      Therefore, high protein nutrition plans prescribed for dialysis patients result in large amounts of phosphorus absorption, of which dialysis only removes 500-600 mg per session.
      • Gonzalez-Parra E.
      • Gracia-Iguacel C.
      • Egido J.
      • Ortiz A.
      Phosphorus and nutrition in chronic kidney disease.
      Because protein intake is an important component of therapeutic treatment in chronic kidney disease adolescent patients, a more suitable dietary approach is to help patients identify high-protein foods that are organic phosphorus sources. This educational tool is designed to help educators teach the difference between organic and inorganic phosphorus and understand the difference in phosphorus absorption from these foods.

      Appendix. A Closer Look at Dietary Phosphorus for Adolescent Kidney Patients

      There are two types of phosphorus in the diet: organic phosphorus and inorganic phosphorus. Talk with your dietitian about which foods you should choose. Eating certain types of phosphorus foods can help manage your kidney phosphorus levels.

      Organic or Inorganic: Which is Better for Phosphorus Control?

      The body absorbs less of the phosphorus from organic food sources, which makes organic a better choice.

      Organic Phosphorus

      • This is found naturally in animal and plant-based foods.
      • Organic phosphorus from animal foods is about 40-60% absorbed in your body.
      • Organic phosphorus from plant foods is even less absorbed.
      • These foods may be higher in total phosphorus, but not all of the phosphorus is absorbed.

      Inorganic Phosphorus

      • This type of phosphorus is added to food during processing as an additive or preservative.
      • Inorganic phosphorus is almost 100% absorbed.
      • Inorganic food sources may be lower in total phosphorus, but almost all of it is absorbed in your body.

      References

        • Goodman W.G.
        • Goldin J.
        • Kuizon B.D.
        • et al.
        Coronary-artery calcification in young adults with end-stage renal disease who are undergoing dialysis.
        N Engl J Med. 2000; 342: 1478-1483
        • Calvo M.
        • Moshfegh A.
        • Tucker K.
        Assessing the health impact of phosphorus in the food supply: issues and considerations.
        Adv Nutr. 2014; 5: 104-113
        • Kalantar-Zadeh K.
        • Gutekunst L.
        • Mehrotra R.
        • et al.
        Understanding sources of dietary phosphorus in the treatment of patients with chronic kidney disease.
        Clin J Am Soc Nephrol. 2010; 5: 519-530
        • Chang A.R.
        • Lazo M.
        • Appel L.J.
        • Gutierrez M.
        • Grams M.E.
        High dietary phosphorus intake is associated with all-cause mortality: results from NHANES III.
        Am J Clin Nutr. 2014; 99 (Available at:) (Accessed June 17, 2016): 320-327
        • Gonzalez-Parra E.
        • Gracia-Iguacel C.
        • Egido J.
        • Ortiz A.
        Phosphorus and nutrition in chronic kidney disease.
        Int J Nephrol. 2012; 2012: 597605