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.
