By Janeen León MS, RD, LD; Srilekha Sarathy-Sayre MS, RD, LD and Catherine Sullivan MS, RD, LD

Phosphorus, potassium, sodium, protein, fat, calories, sugar… navigating a grocery store or restaurant can be challenging and frustrating for someone diagnosed with kidney disease. Eating should be simple, right?

Does Phosphorus Matter to Me?
Most diet needs differ depending on the stage or severity of kidney disease. Not so with phosphorus. Recent studies suggest that even slightly elevated levels of phosphorus in the blood are harmful across all stages of kidney disease.^{(1, 2)} Phosphorus is also a problem for many people with kidney transplants.⁽³⁾ Some studies now link higher phosphorus levels to cardiovascular disease and bone changes in people without a kidney disease diagnosis.^(4-6) 

Phosphorus is tricky. On the one hand it is an essential mineral for our bodies. Phosphorus is needed to form bones and teeth. It helps the body to store and use energy; build and repair cells and genetic material; and makes use of other vitamins and minerals. On the other hand, many foods available in the United States have an over abundance of phosphorus.

Too much phosphorus causes trouble. Various hormones, vitamins and proteins get involved in an attempt to handle excess phosphorus. Kidneys work to filter out excess phosphorus from the body. When kidney function declines, you lose the ability to remove excess phosphorus and phosphorus builds up in the blood. Calcium gets released from bones to combine with the extra phosphorus. The combined calcium-phosphorus mineral complexes get deposited in soft tissues such as the linings of blood vessels, skin, joints and internal organs. The loss of bone calcium causes osteoporosis and other bone diseases. The mineral deposits cause heart and blood vessel diseases and increased rates of death in people with kidney disease and possibly in the general population.

Where is Phosphorus in Your Diet?
Phosphorus may be a natural part of the structure of a food (natural phosphorus) or added as phosphorus-containing food additives during the manufacturing process (phosphorus additives). Natural phosphorus is already part of a food when grown or produced such as in milk, meats, poultry and whole grains. Phosphorus additives are added to foods by food manufacturers and processors for many reasons such as leavening, anti-caking, moisture binding, reducing cooking time, emulsifying or stabilizing, improving texture or maintaining color or firmness. Phosphorus additives are especially a problem because they are almost 100 percent absorbed by the body, whereas only about 60 percent of natural phosphorus is absorbed. Phosphorus additives show up in all types of foods including soft drinks, fruit juices, frozen dinners, bread, chicken, processed and deli meats, sauces, snack foods, baked products, fast foods and restaurant foods.^(7-10)

Become a Label Reader
Persons with kidney disease should limit dietary phosphorus to no more than 800-1,000 milligrams (mg) each day. This is hard because phosphorus content is rarely listed on the nutrition facts panel of a food label. It is sometimes impossible to discover the phosphorus content of restaurant or fast food menu items. Foods sold in the United States are not required by law to state phosphorus content of foods. Some food manufacturers voluntarily label the phosphorus content, but most food labels do not. If phosphorus content is listed on the nutrition facts panel, the number reported includes both natural phosphorus and additive phosphorus. When present, labels may report the percent Daily Value (DV) of phosphorus in a food serving. The percent DV is based on a 1,000 milligram daily requirement. It is easier to calculate the milligrams of phosphorus by adding a zero to the end of the DV percentage number. For example:

25% DV phosphorus → start with 25 then add 0 at end → 250 mg phosphorus

Grab Your Magnifying Glass
Since phosphorus additives are completely absorbed by the body, it is important to limit them as much as possible. The only way to avoid foods with phosphorus additives is to read ingredient lists. The ingredient list is usually found near the nutrition facts label on the packaging. There are many different types of phosphorus additives (see box). You can spot these additives by simply searching for the letters PHOS in the ingredient list.⁽¹¹⁾ For example:

Ingredients: Enriched macaroni product, thiamin mononitrate, riboflavin, folic acid), cheese sauce mix (whey, milkfat, milk protein concentrate, salt, calcium carbonate, sodium tripolyphosphate, citric acid, sodium phosphate, lactic acid, milk, yellow 5, yellow 6, enzymes, cheese culture)

The ingredient listed above contains two phosphorus additives: sodium tripolyphosphate and sodium phosphate. Food items that contain a phosphorus additive should be avoided.

Even if a label reports phosphorus content, it is important to read the ingredient label to search for phosphorus additives. Pay close attention to the labels of processed or manufactured foods such as beverages, frozen prepared foods and meals, baked goods, snack foods, chicken and poultry products, deli meats, cured meats, rice and pasta side dishes and items with sauces.

Many foods have good, lower phosphorus substitutions so you can continue to eat the foods you enjoy. Different flavors of the same food or beverage or different brands of the same type of food may or may not have phosphorus additives. Just read the label. A dietitian knowledgeable about kidney disease can be a great resource to help identify a substitute. Ask your doctor for a referral if you do not have a renal dietitian on your health care team.

Phosphorus additive examples:

Dicalcium phosphate

Disodium phosphate

Monocalcium phosphate

Monosodium phosphate

Potassium tripolyphosphate

Pyrophosphate

Sodium acid pyrophosphate

Sodium aluminum phosphate

Sodium hexametaphosphate

Sodium phosphate

Sodium triphosphate

Tetrasodium pyrophosphate

Tricalcium phosphate

Trisodium triphosphate

Watch Out! Fast Food and Restaurant Food
We have found that most fast food and restaurant foods contain phosphorus additives. In a review of fast food menus, nearly 85 percent of fast food entrees and side dishes contained phosphorus additives.⁽⁸⁾ Be particularly wary of chicken, deli meats, bacon, American cheese, sauces, sandwich buns and French fries. Large portion sizes compound the problem.

If you are prescribed phosphorous binding medication, talk to your doctor about taking a larger dose with restaurant meals. Limiting the number of meals from restaurants can also help you control your phosphorus levels.

Track Your Progress
It is important to track your blood levels. Make sure your doctor or health care team monitors and informs you of your blood phosphorus levels. Also ask about your calcium, parathyroid hormone (PTH) and Vitamin D levels. These all work together to maintain your health. If your blood phosphorus or PTH starts trending up, talk to your doctor about changing your diet or adding medicine to reduce the levels. If your Vitamin D level is low, ask your doctor about replacement doses of Vitamin D. Don’t make these changes on your own. Keeping everything in balance is tricky and should be monitored by your doctor.

Final Thoughts
Phosphorus is trouble in kidney disease, but you have the power to control it. Consider the foods you eat. Look for PHOS in ingredient lists on food labels. Seek low phosphorus and phosphorus-additive free foods to include as part of your regular diet. A simple substitution can make a big difference.

Keep track of your blood phosphorus, calcium, PTH and Vitamin D levels. Work with your health care team by discussing the foods you eat and by being upfront about your use of phosphorus binding medicines.

Lastly, protect yourself or your loved one. Phosphorus control is one area of your health where your choices can make all the difference.

Please visit www.phosfoods.org and www.phosphorus.wikispot.org for more information including helpful handouts on phosphorus additives and restaurant guides for several popular fast food chains. The American Association of Kidney Patients (AAKP) has also developed the AAKP Nutrition Counter: A Reference for the Kidney Patient which lists the phosphorus, sodium, protein, potassium and calories in more than 300 hundred commonly eaten foods. You can download a free copy of the brochure by visiting www.aakp.org/brochures.  
 
References

1. Block GA, Klassen PS, Lazarus JM, Ofsthun N, Lowrie EG, Chertow GM. Mineral metabolism, mortality, and morbidity in maintenance hemodialysis. Journal of American Society of Nephrology. 2004 Aug;15(8):2208-18.
2. Kovesdy CP, Kalantar-Zadeh K. Bone and mineral disorders in pre-dialysis CKD. International Urology and Nephrology. 2008;40(2):427-40.
3. Ambrus C, Molnar MZ, Czira ME, et al. Calcium, phosphate and parathyroid metabolism in kidney transplanted patients. International Urology and Nephrology. 2009 Dec;41(4):1029-38.
4. Dhingra R, Gona P, Benjamin EJ, et al. Relations of serum phosphorus levels to echocardiographic left ventricular mass and incidence of heart failure in the community. European Journal of Heart Failure. 2010 Aug;12(8):812-8.
5. Foley RN, Collins AJ, Herzog CA, Ishani A, Kalra PA. Serum phosphate and left ventricular hypertrophy in young adults: the coronary artery risk development in young adults study. Kidney and Blood Pressure Research. 2009;32(1):37-44.
6. Kemi VE, Karkkainen MU, Lamberg-Allardt CJ. High phosphorus intakes acutely and negatively affect Ca and bone metabolism in a dose-dependent manner in healthy young females. The British Journal of Nutrition. 2006 Sep;96(3):545-52.
7. Kalantar-Zadeh K, Gutekunst L, Mehrotra R, et al. Understanding sources of dietary phosphorus in the treatment of patients with chronic kidney disease. Clinical Journal of American Society of Nephrology. 2010 Mar;5(3):519-30.
8. Sarathy S, Sullivan C, Leon JB, Sehgal AR. Fast food, phosphorus-containing additives, and the renal diet. Journal of Renal Nutrition. 2008 Sep;18(5):466-70.
9. Sherman RA, Mehta O. Phosphorus and potassium content of enhanced meat and poultry products: implications for patients who receive dialysis. Clinical Journal of American Society of Nephrology. 2009 Aug;4(8):1370-3.
10. Sullivan CM, Leon JB, Sehgal AR. Phosphorus-containing food additives and the accuracy of nutrient databases: implications for renal patients. Journal of Renal Nutrition. 2007 Sep;17(5):350-4.
11. Sullivan C, Sayre SS, Leon JB, et al. Effect of food additives on hyperphosphatemia among patients with end-stage renal disease: a randomized controlled trial. Journal of American Medical Association. 2009 Feb 11;301(6):629-35.

Janeen León, Srilekha Sarathy-Sayre and Catherine Sullivan are registered dietitians and clinical researchers at MetroHealth Medical Center and Case Western Reserve University Center for Reducing Health Disparities in Cleveland, OH. Their areas of interest include phosphate-containing additives in the food supply, nutrition in kidney disease, reducing health disparities and access to kidney transplantation. 

This article originally appeared in the March 2011 issue of aakpRENALIFE.

Posted 4/4/2011.

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