by
Priya Sudhindra,
M Sc. (Food & Nutrition), Smt. VHD Central Institute of
Home Sc. Diabetes
Infoline, Apr 2002
Kidney
diseases, whether
acute or chronic, have many causes and associated complications.
Treatment varies depending on the cause and severity of the condition.
Diet therapy plays a major role in the management of the disease since
dietary alterations are a must for effective management.
Given
below are just a few general dietary guidelines, which are discussed in
relation to the functions of the kidneys.
Proteins
in the ‘renal’ diet
As we all know, kidneys play a major role in the excretion of waste
products. The bulk of the solute load is nitrogenous waste products
mainly comprising of urea, uric acid, creatinine and small amounts of
ammonia. The amount of urea excreted is dependant on the protein intake
and increases with a high protein diet. A failure to excrete these waste
products results in their accumulation in the blood leading to a
condition referred to as uremia, a common phenomenon in kidney diseases.
Uremia in turncauses loss of appetite, nausea and reduces taste acuity.
Thus, one of the major goals of diet therapy is to provide adequate
nutrition, minimise uremia and the other metabolic disorders associated
with renal diseases. The load of urea presented to the kidneys is
directly proportional to the amount of protein in the diet; however,
even those on a zero protein diet will produce some amount of urea as a
result of breakdown of tissue protein.
Protein intake has, therefore, to be restricted, generally to 0.5 - 0.6
gm/kg of IBW (ideal body weight). The type of proteins ingested assumes
importance as only a restricted quantity can be consumed. As a general
rule, two-thirds of the proteins should be of a high biological value
and the remainder may be of low biological value.
High biological value proteins are present in eggs, dairy products,
fish, poultry and meat while low biological value proteins are present
in pulses, legumes and nuts - this need to be restricted. Rice is
preferred over wheat because of its lower protein content. Vegetables
and fruits have negligible amounts of protein.
For patients on dialysis, the protein restriction is not so severe.
Patients on haemodialysis are allowed 1 g/kg IBW while those on
peritoneal dialysis are allowed 1.2 g/kg IBW.
Fluid
and electrolyte balance.
It is important to maintain fluid and electrolyte balance. By modifying
the composition of urine, the kidneys maintain the fluid and electrolyte
balance of the body as also the pH of the body fluids.
Water/Fluids
In patients with renal disease the urine output may be affected. The
person may suffer from polyuria (increased volume of urine), oliguria
(decreased volume of urine) or may even be anuric (does not pass any
urine). Odema or water retention is another associated problem.
Fluid intake is therefore carefully measured along with the urine
output. Allowed fluid intake is then calculated as volume of fluid
excreted plus an allowance of 500 ml is given for insensible water
losses. This is usually done everyday in the morning so that the patient
knows exactly how much he can consume.
Salt
Often the patient is hypertensive and hence needs balancing of the salt
intake as well.
Potassium
When kidney function is affected potassium levels may build up in the
body. This affects the functioning of the heart and could lead to
serious complications. However, low potassium levels could also be
dangerous. Hence appropriate adjustments have to be made in the diet. As
a general rule, all fruits and vegetables are high in potassium. Salads,
soups and fruit juices are thus considered taboo items. However, the
potassium content of vegetables may be reduced by leaching (boiling in
extra water and then discard the water).
High Potassium Foods Low Potassium Foods
Fruits and fruit juices Apple, pineapple, papaya, pears, guava
(exceptions)
Coconut and coconut water Honey and sugar
Leafy Vegetables and salad vegetables Sago and arrowroot
Nuts
Jaggery
Instant coffee, chocolate and cocoa
Calcium/ Phosphorus and Vitamin D
Renal Osteodystrophy, (a bone disease) is another complication of
chronic renal failure, which is brought on by abnormalities in the
balance of calcium, phosphorus, vitamin D and the parathyroid hormone.
As the kidney’s filtration capacity loses its ability to clear
phosphate, serum phosphate levels rise. The diet has to be modified to
increase serum calcium levels and reduce serum phosphorus. However, all
foods, which are high in calcium, are also high in phosphorus (e.g. milk
and milk products) and hence the patient is forced to take calcium
supplements or a phosphate-binding raisin. (Phosphate binding raisin
binds phosphorus, which is present in food and prevents its absorption.)
