The low protein diet was developed by dietitians and nutritionists in response to adverse effects that protein can have on persons with kidney or liver disease. Proteins are required for growth, upkeep, and repair of body tissues. They also help the body fight infections and heal wounds. Protein contains 16% nitrogen, which the body eliminates in the urine as urea. In cases where liver or kidney function is impaired, urea, ammonia or other toxic nitrogen metabolites may build up in the blood. The low protein diet is designed to reduce these nitrogen metabolites and ammonia in individuals with liver disease or kidney failure and to reduce the workload on the kidney or liver. If the kidneys, which are responsible for excretion of urea, are not functioning properly (renal failure), or if high levels of protein are continually present in the diet, urea and other toxic nitrogen compounds build up in the bloodstream, causing loss of appetite, nausea, headaches, bad taste in the mouth, and fatigue as well as possibly further adversely affecting the kidney or liver.
The low protein diet focuses on obtaining most of a person’s daily calories from complex carbohydrates rather than from proteins. There are two main sources of protein in the diet: higher levels are found in animal products, including fish, poultry, eggs, meat, and dairy products), while lower levels are found in vegetable products (breads, cereals, rice, pasta, and dried beans). Generally foods in the high protein food group contains about 8 grams of protein per serving. Cereals and grains have about 2 grams of protein in 1/2 cup or 1 slice. Vegetables have about 1 gram of protein in 1/2 cup, while fruits have only a trace amount of protein in 1/2 cup. To control protein intake, foods such as starches, sugars, grains, fruits, vegetables, fats, and oils should be eaten at levels sufficient to meet daily energy needs. If a person has diabetes, the diet must also be designed to control blood sugar.
Protein should never be completely eliminated from the diet. The amount of protein that can be included in the diet depends on the degree of kidney or liver damage and the amount of protein needed for an individual to maintain good health. Laboratory tests are used to determine the amount of protein and protein waste breakdown products in the blood. A suggested acceptable level of protein in a low-protein diet is about 0.6g/kg of body weight per day, or about 40 to 50 grams per day. A person suffering from a kidney disease such as nephrotic syndrome, where large amounts of protein is lost in the urine, should ingest moderate levels of protein (0.8 kg per kg of body weight per day).
A sample menu for one day might include:
Breakfast: 1 orange, 1 egg or egg substitute, 1/2 cup rice or creamed cereal, 1 slice whole wheat bread (toasted), 1/2 tablespoon margarine or butter, 1/2 cup whole milk, hot, non-caloric beverage, 1 tablespoon sugar (optional).
Lunch: 1 ounce sliced turkey breast, 1/2 cup steamed broccoli, 1 slice whole wheat bread, 1/2 tablespoon margarine or butter, 1 apple, 1/2 cup gelatin dessert, 1 cup grape juice, hot, non-caloric beverage, 1 tablespoon sugar (optional).
Mid-Afternoon Snack: 6 squares salt-free soda crackers, 1/2 tablespoon margarine or butter, 1 to 2 tablespoons jelly, 1/2 cup apple juice.
Dinner: 1/2 cup tomato juice, 1 ounce beef, 1 baked potato, 1 teaspoon margarine or butter (optional), 1/2 cup steamed spinach, 1 slice whole wheat bread, 1/3 cup sherbet, 4 apricot halves, hot, non-caloric beverage.
Evening Snack: 1 banana.
This sample menu contains about 1850 calories, with a protein content of 8%.
Special, low protein products, especially breads and pastas, are available from various food manufacturers for persons who need to follow a low protein diet. Specific information on the protein content of foods can be found on food labels. Books that list protein contents of various foods as well as low protein cookbooks are also available.
In addition, it is recommended that fat calories be obtained from monounsaturated and polyunsaturated fats. In order to be effective, some persons may also be required to reduce their sodium and potassium ingestion in foods. Sodium restriction improves the ability to control blood pressure and body fluid build-up as well as to avoid congestive heart failure. Foods with high sodium contents, such as processed, convenience and fast foods, salty snacks, and salty seasonings, should be avoided. Potassium is necessary for nerve and muscle health. Dietary potassium restriction is required if potassium is not excreted and builds to high levels in the blood, which may result in dangerous heart rhythms. At very high levels, potassium can even cause the heart to stop beating.
As kidney function decreases, the kidneys may reduce their production of urine, and the body can become overloaded with fluids. This fluid accumulation can result in swelling of legs, hands and face, high blood pressure, and shortness of breath. To relieve these symptoms, restriction of fluids, including water,soup, juice, milk, popsicles, and gelatin, should be incorporated into the low protein diet. Liver disease may also require dietary fluid restrictions.
Tyrosinemia is a rare but serious inherited disease that may also require the use of a low-protein diet. Tyrosinemia is an inborn error of metabolism in which the body can not effectively break down the amino acid tyrosine.
