Basic principles of nutrition in chronic renal failure

Kidneys are the natural body "filter" helping to remove toxins and excess water from the blood by filtering 200 litres of blood daily and eliminating through urine many substances such as pharmaceutical. In renal patients, the kidneys lose the ability to efficiently filter out blood and eliminate completely the water and toxic substances in urine, resulting in the absence of balance of the components in the blood.

Therefore, a diet is an essential part of a therapeutic treatment of patients with chronic renal failure, both before the final stage, and during the therapy of renal function substitution. Proper diet helps in minimizing uremic toxicity and metabolism wastes, delaying renal disease and leading to a better quality of life. Nutritional needs vary per patient, with albumin concentration in foods to play a dominant role, but in general it is considered necessary to maintain a balance in metals, liquids and electrolytes in the daily diet. Especially, for patients undergoing dialysis it is imperative that they follow a specific diet to avoid malnutrition and undernutrition. The special diet helps significantly in the case of chronic renal insufficiency stressing the importance of decrease in fluid intake, protein, sodium, potassium and phosphorus.

Due to the failure of excretion by the kidney, the general guidance as far as the ingestible liquids are concerned is for the patients with kidney disease to drink less liquid when less urine is shed. Large amount of fluids can be dangerous because excess fluids may increase blood pressure and increase the risk of pulmonary edema and heart failure.

One of the major dietary guidelines for patients with chronic kidney disease is the perceived protein and energy. In this case, moderate consumption of protein is recommended because kidney patients accumulate significant amounts of urea in their blood due to the fact that they cannot excrete urine. Major sources of protein include meat, poultry, fish, egg, milk and legumes. The recommended protein intake for dialysis patients reach 1,2 g protein/ kg body weight/ day and 1.2 - 1,3 g protein/ kg body weight/ day for patients undergoing peritoneal dialysis.

Sodium restriction is also required in the diet, which does not merely suffice in the reduction of its quantity in the food preparation, since around 85% of the sodium we consume is hidden in other foods and only 15% is included in the salt. Foods containing sodium are bread, standardized cheese, salted nuts, frozen products, cereals and canned food.

Normal kidneys excrete excess sodium in the urine and maintain the necessary balance, while in the case of kidney disease, the total daily intake of salt should be limited and much attention should be payed to the natural salt contained in the food. Foods rich in salt contribute to increased thirst therefore fluid intake is recommended, when the volume of urine is reduced to 500-750 ml.

Furthermore, a parameter that must be considered is the potassium intake. Potassium is one of the components in need of limitation. Normal kidneys flush excess but in the case of kidney patients, the kidneys are not working properly, so they do not easily excrete the potassium and develop hyperkalemia (increased amount of potassium in the blood) that can cause muscle weakness and severe heart rhythm disturbances. Potassium is found in most foods, with fruits and vegetables as main sources.

Dietary phosphorus prevention should also be limited to patients with kidney, since the renal dysfunction leads to the deficient excretion of phosphorus and increased levels of blood serum. Phosphorus is abundant in dairy products, eggs and meat. Finally, due to the limited intake of certain food groups, the use of vitamin D and iron supplements is usually recommended by the attending physician to meet the body's needs in valuable vitamins and minerals.

Kalliopi Retsa, Scientific Director at Mesogeios Dialysis Center in Chalkida

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