Our kidneys filter byproducts and waste from our blood. To monitor kidney function, doctors measure serum levels of creatinine, which is made from the breakdown of creatine phosphate from the muscles. Healthy kidneys filter out most creatinine. Higher serum levels of creatinine indicate kidney damage or failure. For this, your doctor will prescribe a renal diet. As your kidneys' workload is lightened and the rate of damage slows, your creatinine levels will become lower. Renal diets focus on controlling protein, potassium, phosphorus, sodium and liquids. Follow your doctor's instructions and do not make dietary or medication changes without consulting him.
Your body uses protein to build and repair tissues and muscles and to fight off infection. When protein is broken down, like any other food, it produces certain waste products. One of these is urea, which damaged kidneys have trouble filtering out of the bloodstream. Most renal diets require you to monitor and limit your protein intake. Your doctor, dietitian or nutritionist will tell you how much and what types of protein you can consume. You will probably be allowed certain amounts of complete proteins from animal sources (lean beef and chicken, for example) and certain amounts of incomplete proteins from plant sources (beans and lentils).
When your kidneys aren't working well, your potassium levels can become too high. This can be serious and even cause sudden heart failure. Potassium is found in many foods, and you must carefully monitor your potassium intake on a renal diet. You may be asked to limit or eliminate leafy green vegetables, broccoli, bananas, potatoes, oranges and apricots, all of which are high in potassium, and encouraged to choose lower potassium foods including cucumbers, carrots, lettuce, apples, cranberries, grapes and rice.
Your body uses phosphorus and calcium to keep your bones strong and to keep your muscles and nerves working normally. Calcium and phosphorus must remain in balance. When you have kidney damage, your body has trouble maintaining this balance. You often end up with too little calcium and too much phosphorus. Your body then steals calcium from your bones to try to restore the proper balance, and your bones become weak and brittle. You may also experience pain in your bones and joints and itchy skin. Foods that are high in phosphorus include sardines, cola, nuts, cheese, liver, peanut butter and beer. You may also be asked to avoid eggs and dairy products.
We need sodium, but most of us consume far more than we need. Avoid foods with added salt, including nuts, bacon, pickles, olives, sauerkraut and luncheon meats. Watch out for salt in processed food products including tinned soup, canned vegetables, sauce mixes and bouillon cubes. Carefully monitor the amount of sodium you consume. Controlling your salt intake may also make it easier for you to control your fluid intake.
When your kidneys aren't working properly, they have problems removing excess fluid from your body. Your doctor may limit your fluid intake to prevent high blood pressure, swelling and shortness of breath. Remember to include soup, ice, ice cream, sherbet and gelatin in your fluid intake.