If you have CKD, you probably have heard that you need to regulate your phosphorus intake. You then might realize that this isn’t as easy as checking for sodium or potassium, the other minerals you may need to watch out for with CKD. Phosphorus can be a bit more challenging than sodium and potassium because unlike those minerals, phosphorus is not included on all nutrition labels. So let’s first understand some basics about phosphorus foods and CKD and phosphorus bioavailability and then take it from there!
What is phosphorus and CKD
You may remember from highschool science class that phosphorus is an element on the periodic table and be wondering how that relates to the human body. But bare with me as we review this. Phosphorus is an essential mineral for the human body and as such is required for many bodily functions. Phosphorus is essential to the structure of our bones and teeth, and also an important component of our DNA, cell membranes, and our energy molecules (ATP).
So if phosphorus has these integral roles in our body why do you need to watch your phosphate intake if you have CKD?
Our kidneys play a very important role in regulating phosphorus levels in our bodies. Too much phosphorus can be dangerous as it can actually remove calcium from your bones, thereby making them more brittle, as well as increasing risk of a heart attack from excess phosphorus leading to calcium deposits in the heart and blood vessels. Therefore, if you have CKD your kidneys may not be able to properly regulate the phosphorus levels, which can cause the complications listed above.
A term you might have heard when trying to understand different phosphorus contents in foods is the term bioavailability. What does bioavailability actually mean though?
Phosphorus foods and CKD
Bioavailability, in the context of phosphorus consumption, means how much of the phosphorus in that food will we actually digest and subsequently absorb in our bodies. This means that even though a food may have a large amount of phosphorus, only a small amount of it might actually get taken up by the body, or vice versa with small amounts of phosphorus having a high level of absorbance in the body. Therefore the bioavailability of the phosphorus in foods is likely a more accurate measure to look at compared to total phosphorus content in foods, in regards to how a food will affect CKD patients.
You may have also heard the term organic and inorganic phosphate and wondered if this is a relevant factor as well. The answer to that question is yes.
Organic phosphates are those found in plant and animal protein sources, whereas inorganic phosphates are found in food additives. This is an important differentiation as organic phosphate has an absorbance rate of 40%-60% whereas inorganic phosphate has an absorbance rate of over 90%. The good news is that inorganic phosphate additives will be listed on the ingredient labels and will therefore be more avoidable. When checking ingredient lists look for ingredients that contain the words phosphate or phosphoric. You can also easily identify phosphorus additives if you see “PHOS” anywhere in the ingredient list. Organic phosphate will not be listed on the label, but you will absorb much less of that phosphorus in comparison to inorganic phosphorus.
This chart below compares the phosphorus bioavailability of some food but this article also has a great pyramid diagram to look at!
Tips for getting enough phosphorus and CKD
Previously you may have been wary of things like beans, whole grain bread, brown rice and nuts, due their high phosphorus levels. Now that we are learning that the bioavailability of the phosphorus in these foods is much lower than others, you can start adding them back in moderate quantities to your diet. For example if you’re looking for a quick and easy snack, trail mix could be a good option. Another example is if you’re looking to make a salad a little heartier, adding kidney beans or chickpeas could be another great option.
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This article was written by Rachel Rosenberg, Nutrition Student Volunteer.
This article was reviewed by Emily Campbell, RD CDE MScFN.