Phosphorus in Chronic Kidney Disease Diet

Phosphorus is the second most abundant mineral in our body, calcium being first, as it makes up 1% of our body. It is mainly found in our bones and teeth; making it important for building strong and healthy functioning bones. Moreover, it plays a crucial role in energy production, as it helps the body produce ATP (Adenosine Triphosphate) molecules.

Insufficient levels of phosphorus in the blood is referred to as hypophosphatemia, which results in muscle weakness and fatigue as energy levels in the body drops. Added to that, it plays an important role in the metabolism of carbohydrates and fats, as well as in the production of protein for the growth, maintenance and repair of cells/tissues in the body. Not to mention, high levels of phosphate in the blood (hyperphosphatemia) is also harmful as it may lead to joint or muscle pain, constipation, diarrhea, nausea or vomiting. In addition, withdrawing calcium out of the bones, leading to calcium deposits in tissues of the lungs, eyes and heart.  

Normally, kidneys aid in the removal of excess phosphorus from the blood. Therefore, patients diagnosed with Chronic Kidney Disease (CKD) may be put on a specialized therapeutic diet that is low in phosphorus, to maintain the patient’s blood phosphorus levels within normal limits (2.5-4.5 mg/dl).

Phosphorus can be found in two different forms, organically or inorganically. Organic phosphorus is found naturally in protein-rich food items, such as meat, fish, poultry, legumes, nuts and dairy products. Furthermore, Phosphorus in plants, especially in beans, peas, cereals, and nuts, is mostly in the form of phytic acid or phytate, which gives relatively low bioavailability of phosphorus, usually 50%, because humans do not express the degrading enzyme phytase. Hence, despite the higher phosphorus content of some plants, the rate of intestinal phosphorus absorption per gram of plant protein compared to animal-based protein tends to be lower.

On the other hand, inorganic phosphorus is added to food as an additive or a preservative to fast food, ready-to-eat meals, canned products and processed food. Not to mention, it is believed that 90% of inorganic phosphorus may be absorbed in the intestinal tract, as opposed to only 40 to 60% of the organic phosphorus present in natural foods. Hence, food additives should be avoided in renal diets; limiting phosphorus intake. This can be managed by reading nutrition labels on packaged food items and avoiding products with added phosphorus.

Naturally, fresh fruits and vegetables of all kinds are low in phosphorus. Therefore, when setting a low phosphorus diet, fruits and vegetables can be consumed normally. However, restricted food items high in phosphorus can be substituted with food items low in phosphorus, for instance, instead of bran cereal and oatmeal, the patient may consume cornflakes and instead of peanuts, the patient may consume low-salt popcorn. Moreover, the serving size of milk in renal diets is half its serving size in regular diets. So, instead of 8 oz. of milk making 1 serving, 4 oz. of milk is provided as a serving in renal diets. Consequently, limiting the amount of phosphorus to half.