Useful Information On Kidney Diseases

End-stage renal disease occurs when the kidneys are chronically unable to function sufficiently on their own, so that dialysis or kidney transplantation becomes necessary to maintain life.

Nutrition may affect persons who have, or are at risk for developing renal disease. The intake of certain nutrients may influence the rate of progression of renal failure in persons with underlying renal disease. High-protein diets can strain the kidneys to the point of failure. This is substantiated by the findings that the prevalence of stone disease in vegetarians is only about 50% of that in the general population. [Robertson, et al] A high intake of animal protein increases the urinary excretion of calcium and oxalate and the accompanying increase in purine intake increases uric acid excretion.

Functioning kidneys regulate the composition and volume of body fluids within very narrow limits. They do so by balancing intake and excretion of body fluids and waste products derived from metabolic processes. If the kidneys fail to maintain homeostasis, a wide range of potentially lethal metabolic disorders can develop throughout the body.

The kidneys remove unwanted salts, waste products, and other chemicals from the plasma along with the water in which they are dissolved. When the concentration of certain salts in urine exceeds the limits of solubility, the salts crystallize and form stones within the kidneys. Treatment of these conditions by diet or drugs is aimed at reducing the concentration of stone-forming substances in the urine. The principal means to this end is to increase urine production by drinking water throughout the day unless on a low-fluid regimen.

The substances found most frequently in kidney stones include calcium, oxalate, phosphate, uric acid, and cystine. Usually these substances are derived from foods, but oxalate and uric acid can also be synthesized endogenously.

Dietary measures to reduce oxalate include restriction of oxalate-rich foods, such as beetroot, rhubarb, spinach, chocolate, and tea, and restriction of excessive intake of ascorbic acid, which is metabolized to oxalate. Uric acid stones are treated with diets low in purine-rich foods, such as organ meats, fish, shellfish, and legumes. Persons with cystine-containing stones respond successfully to low protein diets. Calcium phosphate stones are treated successfully with high-phosphate diets that increase urinary excretion of pyrophosphate, an inhibitor of calcium crystallization.

Chronic renal failure is the consequence of longstanding and progressive renal damage and is usually irreversible. Chronicrenal failure causes extensive disorders in appetite as well as in the body's absorption, excretion, and metabolism of many nutrients. Consequently, nutritional therapy is essential in managing this condition.

The chronic renal failure patient is also likely to accumulate certain potentially toxic chemicals that normally are ingested in small amounts and excreted in the urine. Aluminum is such a toxin; it can cause severe bone disease, dementia, muscle weakness, and anaemia in persons with kidney failure.

Treatment of renal disease may demand severe dietary restrictions or induce nutrient losses. Dietary management of this condition, therefore, must provide protein, energy, and other essential nutrients in amounts adequate to avoid deficiencies but sufficiently restricted to avoid stressing the diminished excretory capacity of the diseased kidney.

The goals of nutritional therapy for both acute and chronic renal failure are to maintain optimal nutritional status, to minimize the toxic effects of excess urea in the blood, to prevent loss of lean body mass, to promote patient well-being, to retard the progression of renal failure, and to postpone initiation of dialysis.

These goals are accomplished with the following methods:-

  • Restricting Fluid Intake:
    Energy, protein, and other essential nutrients are provided in as small a fluid volume as is possible to maintain water balance.
  • Restricting Protein:
    Nitrogen balance must be maintained without any unnecessary accumulation of urea or other toxic nitrogenous waste products. To enhance incorporation of amino acids into body protein and to reduce protein breakdown in more severely ill persons, dietary protein or supplements of high biologic value (containing a high proportion of essential amino acids) are often recommended.
  • Increasing Energy Intake:
    The higher the energy intake, the less dietary protein is required to maintain nitrogen balance. Increasing the carbohydrate and fat content of the diet provides calories that do not stress the compromised excretory capacity of the kidney. Patients with acute renal failure, however, are often unable to tolerate high carbohydrate loads and may require insulin administration.
  • Regulating Phosphate, Calcium, and Magnesium Intake:
    Phosphate restriction is necessary to prevent the metabolic bone disease that often accompanies renal failure, phosphate levels can be regulated with phosphate-binding agents that cause dietary phosphate to be excreted rather than absorbed. Calcium may be administered as a supplement as needed. Excessive magnesium levels are not usually present unless magnesium-containing antacids are used, avoiding them or using magnesium-binding agents prevents toxic accumulation of this substance.
  • Supplementing Vitamins and Trace Elements:
    Supplemental water-soluble vitamins and trace elements are usually used to compensate for inadequate intake and losses in dialysis.
  • Providing Appropriate Counselling and Support:
    Diets for renal patients are based on contradictory principles (meet nutritional needs but restrict protein and phosphorus), are especially restrictive, and require careful monitoring of the patient's nutritional status. Thus, trained nutrition professionals are usually essential for dietary management.

Nutrition Programs and Services

Food Labels:
Evidence related to the role of dietary factors in renal disease currently holds no special implications for change in policy related to food labeling.

Food Services:
Evidence related to the role of dietary factors in renal disease currently holds no special implications for change in policy related to food service programs. [The Surgeon General's Report on Nutrition & Health, 1988.]

  • Robertson, W.G., Peacock, M., Marshall, D.M. and Speed, R. The prevalence of urinary stone disease in practising vegetarians. Fortschritte der Urologie and Nephrologie 17. 1981.

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