The Truth About Potassium, Phosphorus, and CKD

In my 6+ years of working with people with kidney disease, I can tell you this: people mix up potassium and phosphorus ALL the time!

It’s easy to understand why. They both start with “p”. They are both minerals we find in foods. Both show up on lists of “foods to avoid” with kidney disease. And 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.

We will also look at some 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 to know about potassium

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

As a consequence of kidney function damage or loss, potassium levels might 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 patients – to prevent or avoid high potassium levels – is to simply avoid foods that are high in potassium. While potassium in foods may play a role in our blood potassium levels, it’s important to know that there are many other things that contribute to fluctuations in 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

Additionally, recent review articles actually indicate that diet has VERY minimal impact on blood potassium levels – especially naturally occurring potassium found in plant foods. So if your potassium level is high, and your doctor says “just limit high potassium foods” … I encourage you as a patient to advocate for yourself and ask about other potential causes of 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 we mainly find potassium 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. Most people know how sodium can contribute to high blood pressure. But did you know that potassium actually works opposite of sodium to help lower blood pressure? Studies indicate that only a small percentage of the United States population is actually getting adequate potassium in their diets. The solution? Eat more fruits and vegetables.

What to know about phosphorus

Phosphorus is also very important to our bodies! In the human body, we store most of our phosphorus 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 blood phosphorus can mean a greater risk for heart disease and greater 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?

There are several things that can cause high potassium levels.

1. 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. Companies add it to foods to improve flavor or prolong shelf life. We commonly find artificial phosphorus additives in processed and packaged foods and drinks, such as Coke, Hawaiian Punch, powdered lemonades, bakery items, sausages, and lunchmeats.

2. Severe kidney damage which impacts bone health

Did you know the kidneys play a role 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.

3. Inadequate dialysis treatment (for people on dialysis)

Dialysis is an important and life-sustaining treatment for people whose kidneys have failed. During treatments, the dialysis machine removes extra phosphorus from the body, since the kidneys can no longer do that task. “Inadequate dialysis” means something about your treatment plan isn’t working to adequately filter your blood. In this case, your medical team will need to make interventions to fix it. Possible changes might be a longer treatment time or referral to vascular access center, to ensure your fistula is working. Inadequate dialysis is also a result of missing or shortening your dialysis treatments.

How to remember what foods have phosphorus

We find phosphorus in proteins and processed foods. I know, lots of “p” words to remember. But if you can remember the POTAssium/POTAto memory tool from earlier, just remember that phosphorus is “the other one”.

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

Time for my favorite part! 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 section.

Myth #1: Potassium and phosphorus are harmful to the kidneys.

This is FALSE! Natural potassium and phosphorus do NOT harm the kidneys. People with kidney disease may need to limit potassium and phosphorus in the diet, if the kidneys aren’t properly regulating the blood levels. This usually starts to become an issue at an eGFR of 30 or less. For these patients, limiting potassium and phosphorus in the diet can prevent 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…

Myth #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 receive a kidney disease diagnosis, it doesn’t mean you must automatically limit these types of foods in your diet.

Myth #3: Diet is the only thing that causes high potassium and phosphorus.

This is FALSE. We addressed this above. But just as a reminder, there any many reasons potassium may be high. Additionally, phosphorus from the diet is not the only cause of high blood phosphorus.

Myth #4: Plant-based foods are high in potassium and phosphorus, so you should limit them.

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 body only absorbs about 20-50% of the naturally occurring phosphorus in plant foods. As for naturally occurring potassium, we only about 50-60% of it. Plant-based foods also contain fiber and many beneficial nutrients, so it’s good to include them in a balanced diet for kidney disease.

In summary

We find the mineral potassium in plant foods (also milk/dairy). It helps with muscle and nerve function, and alsohelps with blood pressure. Phosphorus is found in protein foods (meat, fish, beans, lentils, nuts). It is a key player in energy production in the body, as well as for 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. Book a free 20-Minute Meet & Greet and we’ll chat about how I can help you. Until then, be well. — Kate, Your Kidney Dietitian