Patients with advanced kidney disease are often perplexed by their nephrologist's recommendation to avoid "dark sodas." As odd as this recommendation may sound, it is based on solid science. While not all dark sodas have to be avoided, some contain high levels of phosphorus, which can cause bone problems in patients whose phosphorus levels are already elevated.
Phosphorus
Phosphorus is present in almost every food, so deficiencies are almost unknown. Phophorus combines with calcium to form hydroxyapatite. Hydroxyapatite makes up bones and teeth. Approximately 85 percent of the phosphorus in the body is found in bone; the balance is found in nucleic acids such as DNA, enzymes and other molecules. In addition to its many functions, phosphorus plays a key role in regulating pH in the body.
High Phosphorus Levels
In healthy people, the kidneys excrete excess phosphorus into the urine. However, this does not occur in patients with advanced kidney disease because the kidneys are too scarred to perform this function. Consequently, serum levels of phosphorus become abnormally high. This condition is called hyperphosphatemia. Hyperphosphatemia is dangerous because the excess phosphorus begins to pull calcium from the bone, leaving the patient vulnerable to fractures.
Low-phosphorus diets are often recommended when serum phosphorus levels exceed 5.5 mg/dl in order to prevent bone problems.
Phosphorus
Dark-colored sodas often contain more phosphorus than kidney patients can safely consume. Since the law does not require food producers to provide information regarding phosphorus content, most patients rely on the online nutrient database provided by the U.S. Department of Agriculture. According to this database, a 12 oz. can of cola has 37 mg of phosphorus. A 12 oz. can of "pepper type" soda has 40 mg. Root beer has none.
Warning
Kidney patients should not stop drinking soda unless their nephrologist specifically advises that they limit their phosphorus consumption. Limiting phosphorus consumption unnecessarily has no preventive benefits. Phosphorus intake does not hasten the progression of kidney disease, so it makes sense to enjoy the foods that you like, within reason.
