What's the deal with phosphorus?

Maybe you’ve heard of it, maybe you haven’t… but you definitely want to know what phosphorus is whether you have kidney disease or not. Phosphorus is an essential mineral that is found in foods. The recommended dietary allowance for adults is 700 mg per day. According to the 2015-2016 National Health and Nutrition Examination Survey (NHANES), adult men consume an average of 1,237 mg phosphorus and adult women consume an average of 1,189 mg daily. Deficiency of this mineral is very rare, and usually it’s not related to a lack of phosphorus in the diet.

What does phosphorus do in the body?

Phosphorus is primarily used for the formation of bones and teeth. It works with calcium to give bones their strong framework. It is also used to make ATP (which is a molecule the body uses to store energy) and helps the body with muscle contractions, maintaining normal heartbeat and nerve signaling.

What happens if I have too much phosphorus?

Healthy kidneys remove extra phosphorus from the blood to keep it in the normal range (which is 2.5 – 4.6 mg/dL for non-dialysis adults). If your kidneys are damaged, they have a harder time removing phosphorus. Phosphorus begins to build up in the blood leading to a cascade of issues.

High phosphorus levels cause calcium to come out of bones which slowly weakens them overtime. Calcium and phosphorus form a complex in the blood and deposit all throughout the body - in blood vessels, soft tissue and organs. Think of these deposits like hard stones. High phosphorus is a big reason people who have kidney disease are more at risk for heart issues and bone disease.

High serum phosphorus may not manifest until the later stages of kidney disease but subtle changes in phosphorus metabolism happen early on. Being proactive is your best defense and preventing high phosphorus. Studies have linked increased phosphorus to cardiovascular disease in non-kidney disease patients as well.

Where is phosphorus found in foods?

Phosphorus is in virtually everything! It’s found naturally in animal proteins, seafood, eggs, dairy, nuts, seeds, legumes, grains, fruits and vegetables. Foods that have protein are good sources of phosphorus – thus meats, seafood, dairy, beans, legumes nuts, seeds are a better source of phosphorus than fruits, vegetables and grains. The type of phosphorus found naturally in foods is known as organic phosphorus.

Phosphorus is also added to many foods. This type of phosphorus is called inorganic phosphorus. It is used in processing for a variety of reasons such as increasing shelf life, improving texture, acting as a pH buffer, and leavening. A study done in Ohio examined the labels of 2,394 best-selling grocery store products and found that 44% of these foods contained a phosphorus additive. Food categories the phosphorus additives were found in included frozen foods (72%), dry food mixes (70%), packaged meats (65%), bread and baked foods (57%), soups (54%), and yogurt (51%). Phosphorus is also added to many beverages including sodas, juices, flavored waters and sports drinks.

How do you know if a food contains phosphorus additives? Check the ingredient list for any ingredient that includes “phos”. Examples are:

• Dicalcium phosphate

• Disodium phosphate

• Monosodium phosphate

• Phosphoric acid

• Sodium hexameta-phosphate

• Trisodium phosphate

• Sodium tripolyphosphate

• Tetrasodium pyrophosphate

Warning - Very few foods list the actual phosphorus content (listed in terms of milligrams or percent daily value) as it’s not required to be tested or reported per the Food and Drug Administration. Don’t assume a food contains no phosphorus simply by checking the nutrition facts and not seeing phosphorus content of the item because I guarantee it does 99% of the time! The more you read the ingredient list the quicker you will get at it! There is also a great app called "phos filter" that you can use- by scanning the bar code of the food it will alert you if the food has added phosphorus.

Organic vs. inorganic phosphorus

The major difference between organic and inorganic phosphorus is the bioavailability. Bioavailability is the rate and extent to which a substance is digested, absorbed and metabolized in the body. For example, simple carbohydrates (sugar for example) are highly bioavailable which means your body is able to absorb and utilize it very easily. Iron found in plant foods (example: spinach) is less bioavailable because other components in that food interfere with its absorption. In terms of phosphorus, whether it comes from natural (organic) sources or man-made (inorganic) makes a big difference. Below shows approximately how much phosphorus is absorbed from foods.

Plant sources (example: beans, nuts, legumes, whole grains) 30-50%

Meat, seafood, poultry and dairy* 60 - 80%

Phosphorus additives (example: cola that has phosphoric acid) 90-100%

These numbers vary slightly based on different studies.

(*animal and dairy products without added phosphorus)

As you can see, phosphorus additives used in food processing are very easily absorbed into the body. Phosphorus from plant foods is less absorbed as the phosphorus is bound to phytate, which is a component of food that the body doesn’t absorb.

Here is a real world example for you…. If you google “kidney friendly diet” and read some of the top articles beans tend to come up on the “do not eat” list as they are “high” in phosphorus (and also the high potassium list – but I’ll address that in another post). One cup of low sodium canned black beans contains about 248 mg phosphorus. Since only a percentage of phosphorus is absorbed in plant-based foods (20-40%), you are only absorbing 50-99 mg phosphorus from the beans! Compare this to chicken breasts… 3.5 oz of chicken contains 220 mg of phosphorus. Phosphorus from meats is more readily absorbed (about 60%) so you are getting around 132 mg of phosphorus. Furthermore… if that chicken breast is processed with sodium phosphate, you could be potentially be absorbing all 220 mg of phosphorus.

So one cup of black beans.... 50-99 mg absorbable phosphorus vs. 220 mg absorbable phosphorus in the chicken breast (with sodium phosphate). It's clear to see that beans are not the enemy when it comes to phosphorus!

How can I consume less phosphorus?

Base your diet around naturally lower phosphorus and plant-based foods such as fruits, vegetables, grains, beans/legumes, nuts and seeds. When purchasing packaged foods (and drinks!) always check the label for the ingredient list – try to find a brand that doesn’t include an ingredient with “phos” in the list. It’s important to avoid added phosphorus in meats and dairy as they are naturally higher in phosphorus... the added phosphorus could almost double your phosphorus load for that meal.

There will be times you may not be able to avoid phosphorus additives and that is okay! If you are making wise choices most of the time you are already on the path to a healthier you!