Phosphorus additives in food and their effect in dialysis patients.

T here is substantial epidemiologic evidence linking hyperphosphatemia and cardiovascular and all-cause mortality among dialysis patients (1,2). Therefore, control of hyperphosphatemia is a crucial element of the routine clinical care of dialysis patients. Theoretically, control of serum phosphorus levels can be achieved by the right combination of decreased dietary phosphorus intake, decreased GI phosphorus absorption by phosphate binders, and increased phosphorus elimination via dialysis. However, the clinical reality is that despite the widespread use of high-efficiency dialyzers, new phosphorus binders, and usual nutritional education, the average serum phosphorus in dialysis patients remains higher than the levels recommended by practice guidelines, except in patients on long nocturnal hemodialysis (3). The lack of attention by practicing nephrologists to dietary phosphorus restriction in general, and more specifically the lack of awareness regarding the increasing consumption of processed foods rich in phosphate additives, may significantly contribute to limit the efficacy of the current interventions (4). Estimation of the dietary intake of phosphorus should consider not only phosphorus contained in natural food, but also phosphorus added in processing food. In general, foods high in protein like meats, milk, eggs, and cereals are also naturally high in phosphorus and traditionally have represented the main source of dietary phosphorus (5). However, this is changing as phosphates are currently being added to a large and increasing number of processed foods, including meats, cheeses, dressings, beverages, and bakery products (6–8). As a result, and depending on the food choices, such additives may increase the phosphorus intake by as much as 1.0 g/d (7). Phosphorus in additives is more readily absorbed than that from foods naturally high in phosphorus; as a result, additives will have a greater effect on hyperphosphatemia than an equivalent amount of naturally occurring phosphorus (5). However, it is of note that Nutrition Facts labels do not include the amount of phosphorus from these additives. It is not widely recognized that the currently available food composition tables in books or software programs do not accurately reflect this additional phosphorus (4,5). For example, when the phosphorus content of several foods measured by chemical analysis was compared with the phosphorus content estimated by three software programs, the latter consistently underestimated the phosphorus content by an average of 250 mg/d (9). When the comparison was made only with menus including six or more processed foods, the underestimation of phosphorus content was greater than 350 mg/d (9). Similar findings have been reported in different geographic areas including Japan (10), Spain (11), and Brazil (12). More recently, a group in Ohio made the same point by analyzing a variety of chicken products bought in stores in greater Cleveland (13). For every category of chicken products containing additives, the actual phosphorus content was greater than the content estimated from the nutrient database (13). The main conclusion from the paper presented in this issue of CJASN is that enhanced meat and poultry products may contain additives that increase phosphorus and potassium content by as much as almost 2-fold and 3-fold, respectively. More importantly, most foods with phosphorus and potassium additives did not list them on their food label (14). The same authors have previously shown that the difference between measured phosphorus content in meat, poultry, and fish foods with or without processing was very significant (14.4 versus 9.1 mg of phosphorus/g protein) (15). These findings imply that better reporting of phosphorus content of foods by manufacturers could result in improved dietary phosphorus control without reducing protein intake to levels risking protein malnutrition (15). These results, together with the findings of other groups mentioned above (7–13), bring home the same strong message: phosphorus-containing additives are present in most meat products and significantly increase the phosphorus content of such products. Moreover, the lack of this information in the Nutrition Facts labels and in the available reference sources, as well as the variation between similar products, prevents patients and dietitians from accurately estimating food phosphorus content and, therefore, phosphorus intake. These findings have important implications for patients, clinicians, and policy-makers. For the average dialysis patient, daily life is a constant struggle with dietary restrictions as well as with poor appetite and sometimes lack of energy to cook. Convenience and fast foods have many advantages for them: they are very accessible and tasty, are generally cheaper than healthier foods, and require Published online ahead of print. Publication date available at www.cjasn.org.