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Hidden Phosphorus in Popular Beverages
| The Issues in Renal Nutrition
in Nephrology Nursing department is designed to focus on nutritional
issues for nephrology patients. Address correspondence to: Deborah Brommage,
Department Editor, Nephrology Nursing Journal; East Holly Avenue/Box
56; Pitman NJ 08071-0056; (856) 256-2320. The opinions and assertions
contained herein are the private views of the contributors and do not
necessarily reflect the views of the American Nephrology Nurses'
Association. |
To
maintain normal serum phosphorus levels, dialysis patient education has
emphasized adherence with phosphate binder prescription and low
phosphorus diet. In addition to the standard advice to avoid dairy
products and legumes, education also focused on lower phosphorus
protein foods and beverages. To meet the public’s demands for more high
quality convenience food, food-processing practices have stepped up the
use of phosphorus additives. These additives are now found in beverages
that were once considered low in phosphorus content.
The renal health care team has been struggling to control serum
phosphorus in patients with chronic kidney disease (CKD) since the
potential harmful effects of hyperphosphatemia became apparent. Through
a National Institutes of Health MedLine literature search, articles
linking elevated serum phosphorus levels and secondary parathyroidism
appear as early as 1966, and links between “persistently high (over 60)
calcium phosphorus product” and cardiac calcification as early as 1975
(Arora, Lacy, Schacht, Martin & Gutch, 1975, p. 4). By 1975, there
was enough evidence between phosphorus levels and renal osteodystrophy
for the American Dietetic Association to issue its recommendation of
restricting phosphorus intake in this population in hopes that “the
bone lesions of secondary hyperparathyroidism and osteomalacia may be
minimized and even prevented” (Schoolwerth & Engle 1975, abstract).
Today, there is further evidence (Block, 2004, Kestenbaum et al. 2004)
to link altered mineral metabolism with cardiac calcification and death.
In 2003, the National Kidney Foundation released the K/DOQI Clinical
Practice Guidelines for Bone Metabolism and Disease in Chronic Kidney
Disease. The guidelines established targets for optimal calcium,
phosphorus, calcium phosphorus product, and intact parathyroid levels.
They also emphasized the need to meet these goals in order to minimize
the CKD’s risk of morbidity and mortality.
Medications such as sevelamer HCl and cinacalet HCl have helped
patients reach calcium and PTH target however, hyperphosphatemia
continues to be an ongoing problem.
To maintain dialysis normal serum phosphorus levels, patient education
has emphasized adherence with phosphate binder prescription and
maintenance of a low phosphorus diet. In addition to the standard
advice to avoid dairy products and legumes, education also focused on
lower phosphorus protein foods. Nurses and dietitians continued to
encourage patients to avoid colas and “pepper” style beverages and
rallied behind root beer, iced teas, and other “clear” beverages. They
were considered safe. That is, until now…
Phosphorus Additives
As
Americans continue to demand high quality convenience food,
food-processing practices have stepped up the use of phosphorus
additives to ensure the quality and flavor that American’s have come to
expect. In a recent article, Uribarri & Calvo (2003) report the
most notable products using phosphorus additives are restructured meats
(chicken nuggets and hotdogs), processed and spreadable cheeses,
“instant” products (puddings and sauces), refrigerated bakery products,
and beverages.
Furthermore, Calvo (2000) states that in 1990, phosphorus additives
contributed to an estimated 470 mg/day to the American diet, and with
the insurgence of the new foods, additives could now contribute up to
1000 mg/day depending upon an individual’s food choices.
What Makes This Problem Unique to the Renal Community?
What
makes this problem unique to the renal community is that these
phosphorus additives are highly absorbable. In a typical mixed diet of
grains, meat, and dairy, only 60% of the dietary phosphorus is
absorbed, whereas phosphoric acid and various polyphosphates and
pyrophosphates are almost 100% absorbed (Bell, Draper, Tzeng, Shin,
& Schmidt 1977). Diets higher in these inorganic salts will result
in higher phosphorus absorption.
Trying
to identify these new, higher phosphorus foods can be challenging.
Manufacturers are no longer required to list the phosphorus content on
the food label. As a result, if the company does analyze the product
for phosphorus, it is sometimes classified as “proprietary” information
or buried so deep and so far away that customer service representatives
have to turn the request for information over to one or two different
departments. Even then, there is no guarantee that the company can
locate the information. Another challenge is the practice of products
being affiliated with one company and manufactured, packaged, and
distributed by another company. For example, Country Time Lemonade®
is considered a Kraft®-brand food, but some Country Time
Lemonade® products are manufactured and distributed through Dr.
Pepper/7-Up®. Finally, each company formulates its products
differently, and within each product, the individual delivery packages
may be formulated differently. For example, the ingredients in a
bottled iced tea may be different than that of the same brand of canned
iced tea.
Table
1 presents the phosphorus content of some commonly consumed beverages.
You may be surprised to see that Hire’s® root beer contains
phosphorus, that Diet Coke® has less phosphorus than any other diet
cola, and that a 12-ounce can of Nestea Cool® iced tea has more
phosphorus than 4 ounces of milk!
As
this table indicates, it is important that we continue to educate
patients on dialysis on the importance of reading labels and sharing
the “safe” brands they find, and to notify us of “unsafe” brands.
References
Arora,
K.K., & Lacy, J.P.(1975). Calcific cardiomyopathy in advanced renal
disease. Archives of Internal Medicine, 135, 603-605.
Bell R.R., Draper H.H., Tzeng D.Y.M., Shin
H.K., & Schmidt G.R. (1977). Physiological responses of human adult
to foods containing phosphate additives. Journal of Nutrition, 107,
45-50.
Block, G.S. (2004). Mineral metabolism,
mortality, and morbidity in maintenance hemodialysis. Journal of the
American Society of Nephrology, 15, 2208-2218.
Calvo M.S. (2000). Dietary considerations to prevent loss of bone and renal function. Nutrition,16, 564-566.
Kestenbaum, B., et al.(2004) Serum
phosphate level and mortality risk among people with chronic kidney
disease. Journal of the American Society of Nephrology, 16, 520-528.
National Kidney Foundation. (2003). NKF
K/DOQI: Clinical practice guidelines for bone metabolism and disease in
chronic kidney disease. American Journal of Kidney Diseases, 42,
Supplement 3.
Parfitt, A.M. (1969). Soft-tissue calcification in uremia. Archives of Internal Medicine, 124, 544-556.
Schoolwerth A.C., & Engle, J.E.(1975)
Calcium and phosphorus in diet therapy of uremia. Journal of the
American Dietetic Association, 66, 460-464.
Stanbury, S.W., & Lumb G.A. (1966).
Parathyroid function in chronic renal failure. A statistical survey of
the plasma biochemistry in azotaemic renal osteodystrophy. Quarterly
Journal of Medicine, 35, 1-23.
Uribarri J., & Calvo M.S. (2003) Hidden
sources of phosphorus in the typical American diet: Does it matter in
nephrology? Seminars in Dialysis, 16, 186-188.
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