A reduced-protein diet can lower the concentration of urinary substances (substances that must be excreted in the urine) to keep symptoms at bay and delay the start of dialysis treatment or kidney transplantation as long as possible. Less protein means a lower burden. The normal average diet for a healthy person contains 1.0 to 1.5 g of protein per body kilogram of body weight. This is too much for diseased kidneys.
Protein: finding the right dose
For the diet of a patient with chronic renal failure, limiting protein intake is always a kind of “tightrope walk,” because it quickly creates the risk of undersupply of vital amino acids. Amino acids are building blocks of proteins (albumen) and have other functions in the body besides building body mass. They act as enzymes, hormones, antibodies in the immune defense, the transmission of nerve impulses and much more. In case of energy deficits, both the body protein and the little allowed food protein are used for energy supply. This in turn leads to an undesirable increase of urea (breakdown product of protein) in the blood. However, the requirements for diet composition depend on the different phases of chronic renal insufficiency and are based on laboratory values. By adapting their diet, affected individuals can actively influence the course of the disease.
Protein (egg white)
Dietary protein should be limited according to the severity of chronic renal failure. However, as a minimum of dietary protein, it should not be less than 0.5 g of protein per body kilogram to prevent body substance breakdown. Patients with advanced renal insufficiency should generally allow their daily protein intake to level off at 40 to 60 g.
- It is recommended to use low-protein dietary special products (low-protein starch, low-protein flours and products made from them, such as bread and pastries).
- Select biologically high-quality protein to provide the essential amino acids in sufficient form. High-quality protein blends are ensured by combining potatoes and egg, beans and egg, milk and wheat, egg and wheat, legumes and wheat, and legumes and milk. The potato and egg mixture has the highest biological value (= number of grams of body protein that can be built from 100 g of dietary protein).
Fat
In addition to providing energy, fats are suppliers of essential fatty acids and carriers of fat-soluble vitamins.
- Place emphasis on an adequate fat intake with plenty of monounsaturated fatty acids (eg, olive oil or canola oil) and polyunsaturated fatty acids (eg, corn oil or safflower oil).
Carbohydrates
The various sugars are pure carbohydrates and can be used in usual amounts. It may be necessary to fortify the diet with carbohydrates to provide adequate energy.
- Carbohydrate sources such as bread, pastries and pasta also contain protein and should be replaced in whole or in part with low-protein specialty products in advanced kidney disease.
Energy
Care must be taken to ensure adequate energy intake, because if the energy intake is insufficient, the body will use the already limited food protein for energy. The result is the undesirable increase of urinary substances in the blood.
- Consume at least 35 to 40 calories per kilogram of body weight per day. Carbohydrates such as dextrose, table sugar, or prescribable dietary foods (low in protein and electrolytes and high in energy at the same time), can be used for energy fortification. A fat enrichment of the food is also possible by adding diet margarine.
- Check your weight daily and consult your doctor and dietician in case of severe weight fluctuations.
Water
The ability of the kidney to excrete water does not diminish until the final stages of the disease. Until then, to relieve the kidney, a high fluid intake of 2 to 3 liters is necessary to flush out the urinary substances. In general, to avoid edema (water retention), the following golden rule applies:
- Drink as much as the amount of urine excreted the day before plus 500 ml.
Sodium
Sodium affects blood pressure and is closely related to the patient’s sense of thirst.
- Be moderate with table salt and prefer fluoridated iodized salt. The daily diet should not contain more than 6 to 8 g of table salt in total. This is the case with the average diet. When cooking if possible not at all or add salt only at the table.
- Do not use dietary salts. These are products that consist entirely or partly of potassium salts and can cause hyperkalemia.
- All ready meals, sauces or broths have a high salt content.
Potassium
Potassium excretion remains largely normal until an advanced stage of chronic renal failure. A low-potassium diet is usually required only when urine output has decreased sharply (less than 1000 ml per day). Elevated blood potassium levels can be very dangerous, causing muscle weakness, cardiac arrhythmias, and even heart failure. Since potassium is a water-soluble mineral, the potassium content of potatoes, vegetables and fruits can be reduced by appropriate preparation and cooking.
- Avoid potassium-rich foods such as spinach, legumes, tomato paste, dried fruits, apricots, bananas, chocolate, nuts, dried fruits, vegetable and fruit juices.
- Reducing the potassium content (10 to 50 percent) of fruits, vegetables, salads and potatoes is achieved by cutting them into small pieces and watering them several times.
- Do not continue to use the cooking water of vegetables and potatoes.
- Omit the juice of canned fruit and prepare yourself a fresh lemon marinade.
Phosphorus/phosphate
A low-protein diet is usually low in phosphate at the same time. Daily phosphate intake should not exceed 1000 mg per day, otherwise problems with bone metabolism may occur.
- Foods high in phosphate are hard and processed cheeses, nuts, whole grains, dried porcini mushrooms, smoked foods, chocolate and cola drinks.
- If dietary phosphate reduction is not sufficient, additional medication (phosphate binders) must be given by the doctor, which prevent phosphate absorption in the intestine.
Vitamins and other minerals
A diet low in protein and potassium can lead to deficiencies in vitamins and minerals in the long term.
- It is important to have a targeted substitution of calcium, iron, zinc, vitamin D, vitamins of the B-complex and the water-soluble vitamins by the doctor.
Constipation (constipation) in renal failure.
In the end stage of chronic renal failure, constipation often exists due to low fluid intake. Consumption of fiber-rich foods such as whole grains, fruits, vegetables, and salads usually ensures healthy bowel function and a reduction in the incidence and severity of diet-induced hyperlipidemia (dyslipidemia). Because elevated levels of potassium or phosphorus limit consumption of these foods, the risk for constipation is higher. Due to delayed bowel emptying, it can cause bloating, flatulence and abdominal pain. Taking conventional laxatives can lead to dependence. For the treatment of constipation, a lactulose preparation is recommended for chronic renal insufficiency patients in the pre-dialysis stage and dialysis stage. For many patients and their relatives, the realization that they are affected by chronic kidney disease and have to adjust to it represents a profound change in their life story and life planning. In addition to all the medical necessities that patients face, nutritional therapy is part of the ways to delay the progression of chronic renal failure.