Healthy kidneys keep serum potassium levels within a very narrow range regardless of how many high-potassium foods you eat. Kidneys of people with advanced kidney disease are less able to perform this function, so potassium levels often begin to creep up. If this occurs, your nephrologist might recommend a low-potassium diet to keep things under control.
Advanced Kidney Disease
Potassium levels begin to become elevated when the patient's glomerular filtration rate, or GFR, drops to 30 to 59 mL/min/1.73 m2. Kidney function is roughly approximate to GFR, so someone with a GFR of 59 has 59 percent function. Nephrologists routinely monitor potassium levels every time they order lab work so that they can respond to this problem promptly.
Regulation of potassium is important because nerves only function properly when the concentration of potassium is between 3.5 and 5.0 mEq/L. When nerves begin to misfire, the heart beats irregularly. The National Kidney Foundation notes that levels higher than 5.0 mEq/L indicate that a low-potassium diet is needed. Levels higher than 6.0 are a true medical emergency.
A low-potassium diet is confusing because no easy way to identify high-potassium foods exists. Using a potassium counter, such as the database provided by the U.S. Department of Agriculture, is very helpful. Some high-potassium foods include bananas, avocados, oranges, tomatoes and broccoli. Low-potassium foods include green peppers, onions, mushrooms and fresh peas. Portion size is very important. For example, 1 cup of watermelon can be eaten safely. However, more than one cup is considered a high-potassium food.
Most kidney patients find meeting with a renal dietitian to be very helpful. The renal dietitian can evaluate your diet, identify areas where potassium can be eliminated and make menu suggestions. The dietitian can also speak to other nutrients that might be problematic, such as phosphorus, protein, sodium and vitamin D.