Potassium And Phosphorus Are Not The Same Thing – Here’s The Difference

confused looking dietitian with the words "potassium" and "phosphorus" in large print

Having worked with people with kidney disease for the last five years, I can tell you this: people get potassium and phosphorus mixed up ALL the time!

It’s easy to understand why. They both start with “p”. They are both minerals found in foods. They both show up on lists of foods to avoid with kidney disease. They kinda sound the same!

But – they are not one and the same! In this article we’ll take look at some of the differences and how to tell them apart.

Make sure to read allllll the way thru this article – I’m also addressing some of the most common myths about potassium and phosphorus – and you definitely want to be aware of these things!

NOTE: the intended audience for this article is people with kidney disease, caregivers of people with kidney disease, or medical professionals.

What you need to know about potassium

Potassium is a mineral that’s incredibly important to keep our bodies functioning properly. It helps our nerves and muscle to function, and it also helps regulate blood pressure. It is important that our body has an adequate amount of potassium.

When kidney function has been damaged, potassium levels can sometimes become elevated in the body. High levels of potassium in the blood can cause fatigue, weakness, nausea, shortness of breath, and dangerous changes in heart rhythm. One of the common recommendations given to patient, to avoid these high potassium levels, is to simply avoid foods that are high in potassium. The potassium in foods may play a role in our blood potassium levels, but it’s good to keep in mind that there are many other things that contribute to high potassium levels…

What can cause high potassium, BESIDES your diet?

This is not an exhaustive list, but these are common causes:

  • acidosis (condition associated with kidney disease where the blood becomes more acidic)
  • certain medications, such as NSAIDS, ACE inhibitors, ARBs, potassium-sparing diuretics, or beta-blockers
  • insulin deficiency
  • tissue breakdown (such as burns or trauma)
  • GI problems such as constipation

Some recent review articles actually seem to indicate the diet has VERY minimal impact on blood potassium levels. So if your potassium level is high, and your doctor says “just limit high potassium foods” … I’d encourage patients to advocate for themselves and ask about other potential causes of their high potassium levels.

Now – in case you are following a low potassium diet, how can you remember which foods have potassium? Here’s a simple way to remember.

POTAssium is in POTAtoes. Potatoes are a vegetable. And potassium is found mainly in fruits and vegetables. Some of the highest potassium vegetables and fruits include leafy greens, mushrooms, beans, melon, tomatoes, avocado, winter squash, banana, melon, oranges, and dried fruits (raisins, apricots).

Many Americans could actually use MORE potassium in their diets. Potassium works opposite of sodium to balance blood pressure levels, and it’s been reported that only a small percent of the United States population is getting adequate potassium in their diet. The solution? Eat more fruits and vegetables.

What to know about phosphorus

Phosphorus is also very important to our bodies! In the human body, most of our phosphorus is found in our bones and in our teeth. Phosphorus also helps to produce energy in our bodies.

Phosphorus levels in the blood can ALSO become too high in people with kidney disease. This tends to happen in the later stages of kidney disease, when the kidneys have greater amounts of damage and cannot properly filter excess phosphorus out of the blood.

When there is too much phosphorus in the blood, it can be damaging to the heart, blood vessels, skin, and muscles. Phosphorus can bind with another mineral, calcium, to form stones that deposit in the soft tissues of the body… and that shouldn’t be happening. This is particularly dangerous when these little stones wind up in the heart and blood vessels. High phosphorus is known to be related to an increased risk of heart disease and increased risk for cardiac events in people with kidney disease.

Long story short – we REALLY want to make sure we don’t high high blood phosphorus levels.

What causes high phosphorus?

The first thing that can cause high phosphorus is too much phosphorus in the diet. It’s important to know that there are different types of phosphorus in the diet:

  1. Organic phophorus – this kind is naturally occurring in foods such as beans, nuts, and whole grains. Organic phosphorus is different than “organic” in the sense of organic farming (i.e. foods farmed without certain types of pesticides).
  2. Inorganic phosphorus – this type of phosphorus is an artificial phosphorus, added to foods to improve flavor or prolong shelf life. This added, artificial phosphorus is commonly found in processed and packaged foods and drinks, such as Coke, Hawaiian Punch, powdered lemonades, bakery items, sausages, and lunchmeats.

The second thing that can cause high phosphorus is severe kidney damage that impacts bone health. Did you know the kidneys are involved in keeping your bones healthy? Yup! When the kidneys are damaged, altered levels of hormones in the body can pull phosphorus out of the bones and into the bloodstream. These changes in bone health can cause the bones to become weak and at risk for fracture. Even if it doesn’t get to that point, it can definitely cause bone and joint pain. You want to avoid all those things if you have kidney disease.

And the third thing that can cause high phosphorus – for people on dialysis – is inadequate dialysis treatment. One of the MANY reasons dialysis is important and life-sustaining is that it removes extra phosphorus from the body, since the kidneys can’t filter out the phosphorus anymore. “Inadequate dialysis” can mean either your treatment isn’t filtering your blood well enough (in which case, your medical team will need to make interventions to fix it), or it could mean missed or shortened dialysis treatments.

Now – how do we remember which foods have phosphorus? Phos tends to be found in proteins and processed foods. I know, lots of “p” words to remember. But if you can remember the POTAssium/POTAto memory tool, just remember that phosphorus is generally found in all the other foods: proteins and processed foods.

Take note: some foods do contain BOTH potassium and phosphorus: such as beans, lentils, nuts, whole grains, and dairy products.

Myths about potassium and phosphorus (BE SURE TO READ THIS!)

That’s not all, folks! There are a few MAJOR myths circulating about potassium and phosphorus, and you need to know about these myths and misconceptions. Don’t even think about skipping over this part: 

  1. “Potassium and phosphorus are harmful to the kidneys” – this is FALSE! Potassium and phosphorus do NOT harm the kidneys. These minerals might need to be limited in the diet for people with kidney disease, because the kidneys are not working properly to control the levels of these minerals in the blood. Therefore, people with kidney disease may need to take steps such as limiting how much potassium and phosphorus they eat, to prevent the blood levels from getting too high. But, potassium and phosphorus DO NOT cause damage to the kidneys themselves. Got it? 🙂 Potassium and phosphorus do NOT cause kidney damage. This leads us to myth number 2…
  2. “Everyone with kidney disease should limit potassium and phosphorus” – this is a MYTH! Your body needs both potassium and phosphorus to function properly. If your potassium and phosphorus levels are normal, you don’t need to make any adjustments to your diet. In fact, being overly restrictive of potassium and phosphorus could lead to low blood potassium and phosphorus levels. Just like high potassium/phosphorus levels, LOW potassium/phosphorus levels can be a problem for the body as well. Just because you are diagnosed with kidney disease, it doesn’t mean you must automatically limit these types of foods in your diet.
  3. “Diet is the only thing that causes high potassium and phosphorus” – this is FALSE. We addressed this above, but just a reminder that there any many reasons potassium could be high, and phosphorus from the diet is not the only cause of high blood phosphorus.
  4. “Plant-based foods are high in potassium and phosphorus, so they should be avoided” – this is a MYTH! Foods such as beans, lentils, and whole grains DO contain both potassium and phosphorus. But foods such as meats and dairy milk contain just as much, if not more. Additionally, the type of phosphorus found in plant foods is only about 50% absorbed by the body, so you aren’t actually getting the full amount listed. Plant-based foods actually contain fiber and lots of beneficial nutrients, so it’s good to include them in a balanced diet for kidney disease.

In summary

Potassium is found in plant foods (also milk/dairy), helps with muscle and nerve function, and helps with blood pressure. Phosphorus is found in protein foods (meat, fish, beans, lentils, nuts) and it is a key player in the production of energy in our bodies, as well as bone health.

There are many myths about potassium and phosphorus, but if you remember just ONE, I want it to be this: not everyone with kidney disease needs to limit potassium and phosphorus. The diet for kidney disease is not a one size fits all plan, and you should eat according to YOUR lab results.

Having trouble figuring out what to eat? Meeting with a renal Registered Dietitian (like me!) can help clarify things. Be sure to send me a message if you’re confused, and we’ll talk things out. — Kate, Your Kidney Dietitian

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