Phosphorus and kidney disease

Many of my patients with chronic kidney disease (CKD) frequently ask me about the proper diet they should have to delay the worsening of their kidney problem. One element that CKD patients should watch out for is the mineral phosphorus.

Phosphorus is an essential mineral in the body. It makes up part of our bones and teeth -- and even our DNA. It helps the body function properly and uses energy from the food we eat. Phosphorus is naturally present in many foods, and a phosphorus deficiency is rare if you have a balanced diet with no need to take supplements.

The recommended nutrient intake of phosphorus for adult Filipinos is 700 mg per day; 1,250 mg for adolescents and teenagers, when bones are growing the most. The average daily consumption of adults is about 1,200 to 1,500 mg/day and the upper tolerable level is about 3,000 to 4,000 mg/day, but high phosphorus intakes rarely produce adverse effects in healthy people.

The kidneys, intestines and bones regulate phosphorus levels in the body. When the kidneys stop working properly, as in CKD, the body cannot get rid of phosphate properly and phosphorus levels go up. Too much phosphorus in the body makes calcium come out of the bones, making them weak and prone to fracture. This misplacement of calcium can also affect blood vessels and cause blood pressure and heart disease. It is, thus, very important for patients with kidney disease to watch their phosphorus intake, limiting it to about 800 mg per day.

Many different types of foods contain phosphorus — meats and poultry, organ meats (liver), fish, dairy products, eggs, nuts, beans, vegetables and grains, including bread and rice. On average, an ounce of meat has about 65 mg of phosphorus, and a cup of milk or yogurt about 220 mg. A cup of white rice has about 70 mg of phosphorus, and a cup of long-grain brown rice has about 200 mg. While whole grain bread can be a healthy source of fiber, one slice has about 40 mg of phosphorus compared to white bread with 25 mg.

Patients with CKD are usually advised to limit their phosphorous by limiting their protein intake and to replace animal proteins with plant-based protein sources. Care should also be taken when eating processed and frozen foods, which can contain phosphate additives, which are used to preserve or stabilize these foods. About 70 percent of phosphorus from natural food sources is absorbed by the body, and 100 percent of phosphorus is absorbed from processed foods.

One way to limit phosphorus intake is to check the ingredient list of processed foods for the letters “phos” for additives, such as phosphoric acid, disodium phosphate, sodium pyrophosphate and sodium polyphosphate. These additives can add almost 70 mg of phosphorus to your diet. Also look out for phosphorus in drinks like colas (they contain phosphoric acid), flavored waters, iced teas, bottled juices and bottled coffee.

It can be difficult for patients with CKD to manage their diets and many ask, “What can I eat?” because they also often have other health conditions, such as hypertension and diabetes. Here are some examples and ways to prepare foods that are lower in phosphorus:

Chicken thigh, skinless, three ounces = 190 mg

Old-fashioned rolled oats (instead of instant), ½ cup cooked = 120 mg

Shrimp, three ounces = 120 mg

Almond milk, ½ cup = 50 mg

Potato, without skin, medium size (2 inches diameter), double-boiled = 50 mg

Spaghetti noodles, ½ cup = 42 mg

Apple, medium size = 10 mg

Egg white, from 1 egg = 5 mg (1 whole egg with the yolk has 95 mg of phosphorus)

Patients with CKD should opt for whole foods rather than processed or fast food. Check labels for ingredients of hidden sources of phosphorous. Many online sources list the amount of phosphorous per serving for many common foods. Portion control can also help limit the amount of phosphorus per meal. And remember that eating too much low-phosphorus food makes it a high phosphorus food.