Tue, 26 May 2015

Spotlight on phosphorus: the nutrition facts table’s missing mineral

By Emily Robins, Dietetic Intern, Grand River Hospital – Kitchener, ON

Over the past four weeks I have had the opportunity to intern under the supervision of June Martin, Registered Dietitian for the Grand River Regional Renal Program. I have spent most of my time here working with patients in the hemodialysis unit, assessing their nutritional status and providing nutrition intervention and counselling as needed.

As a student I learned that one of the functions of the kidneys is to remove extra phosphorus (an essential mineral that occurs naturally in our food, water, and bodies) from our blood and excrete it in our urine. Some phosphorus is required for growth, maintenance, and repair of all body tissues, as well as healthy bone formation and growth. But for someone with chronic kidney disease, having too much phosphorus in their blood for a long time, can make their bones weak, and cause minerals to build up in places they shouldn’t, like the heart, blood vessels, lungs, skin, and joints. Large amounts of phosphorus in the blood are also strongly linked with cardiovascular diseases and events, and death, in persons with or without chronic kidney disease1

Although normally our kidneys do a good job of removing extra phosphorus from our blood, sick or damaged kidneys aren’t so great at it. This can mean that for someone with chronic kidney disease the total amount of phosphorus in his or her blood may rise above what is normal. One of the best ways to prevent this from happening is by following a low phosphorus diet, as prescribed by your Registered Dietitian.

As a student, the idea of a low phosphorus diet didn’t seem like such a big deal. As an intern, where I tell real people to follow real diet advice, I have learned this can be quite tricky.

There are two main sources of phosphorous in our food: organic and inorganic. Organic phosphorus is found mainly in animal and plant-based protein foods like chicken, egg yolk, milk, lentils, and nuts, while inorganic phosphorus refers to phosphorus contained in food additives2. Phosphorus additives are used in a variety of food products including breads, cereals, dairy products, pasta, meats, seafood, and canned fruits and vegetables3 to improve the appearance, texture, and shelf life of the food product4.

Although animal and plant-based protein foods are abundant in organic phosphorus, our bodies only absorb about sixty-percent of naturally occurring phosphorus from animal sources, and less than forty-percent from plant sources2,5. When it comes to inorganic phosphorus from food additives however, we absorb almost one hundred percent of what we take in2,5.

The need for phosphorus on food labels
One of the real challenges of following a low phosphorous diet is that neither naturally occurring nor added phosphorus is reported on the Nutrition Facts Table. This creates several problems. First, because it is not commonly known that some food additives contain phosphorus, patients with chronic kidney disease may be eating large amounts of phosphorus without even knowing it! Second, if patients don’t know that they are eating foods with added phosphorus, it’s less likely that these foods will be identified as problematic during a diet recall or interview, which may result in a less accurate nutrition assessment and missed teaching opportunities.

Lastly, while checking the ingredients list for phosphorus additives is a good place to start, it can be a discouraging task. Ingredients lists are long, the print is small, and they still don’t tell us how much phosphorus is in a food product. From an educational perspective, knowing the amount of phosphorus in a food product − both organic and inorganic − would make it easier for patients to choose which phosphorous-containing foods are better food choices than others, and paint a clearer picture of how certain foods fit into their total intake for one day.

Life for dialysis patients is difficult for many reasons including tight diet restrictions, poor appetite, and lack of energy to cook. Having this information available at point-of-purchase would make it that much easier for patients to stick with their renal diet. Complete avoidance of processed or convenience foods is difficult for anyone, but especially for the dialysis population. Having the amount of phosphorus on the nutrition facts table would empower patients to make better food choices within their means.

Take home messages
International and national authorities should devote more attention to including the amount of natural or added phosphorus in a food product on the nutrition facts table.

For now, here’s what you can do to limit your phosphorus intake:

  1. Check the ingredients list: look for ingredients with the word “phosphorus” or “phos” in them. Limit or avoid these food products.
  2. Limit your intake of processed foods: not only do processed foods contain phosphorus additives, but they are often quite high in salt, and provide less nutritional value than a diet built around whole foods. Limiting processed foods is a good rule for anyone!

Looking for new recipes?  Ask your dietitian about the newest recipes on Spice It Up! or check out www.renalrd.ca for information about a new, patient friendly cookbook.

References
1. Leon, J., Sullivan, C., & Sehgal, A. (2013). The prevalence of phosphorus containing food additives in top selling foods in grocery stores. Journal of Renal Nutrition. 23(4), 265-270. doi: 10.1053/j.jrn.2012.12.003
2. Noori, N., Sims, J., Kopple, J., Shah, A., Colman, S., Shinaberger, C., Bross, R., Mehrotra, S., Kovesdy, C., & Kalantar-Zadeh, K. (2010). Organic and inorganic dietary phosphorus and its management in chronic kidney disease. Iranian Journal of Kidney Diseases. 4(2), 89-100. 
3. International Food Additives Council. (2015). Phosphates. Retrieved from: http://www.foodadditives.org/phosphates/phosphates_used_in_food.html
4. Benini, O., D’Alessandro, C., Gianfaldoni, D., & Cupisti, A. (2011). Extra phosphate load from food additives in commonly eaten foods: a real and insidious danger for renal patients. Journal of Renal Nutrition. 21(4), 303-308. doi:10.1053/j.jrn.2010.06.021 
5. D’Alessandro, C., Piccoli, G., & Cupisti, A. (2015). The “phosphorus pyramid”: a visual tool for dietary phosphate management in dialysis and CKD patients. BMC Nephrology. 16(9), 1-6. doi:10.1186/1471-2369-16-9