Changing patterns of diet in patients with kidney disease
Traditionally diet plays an important role in any disease. The first doubt the patient has is what to eat when he has any medical problem. To understand the concept of diet in patients with kidney disease, we should know briefly the functions of the kidneys.
Basically the kidneys excrete the products of metabolism. The food we eat is broken down into simpler components and after absorption energy is produced in the body. The most important component of the food i.e. protein is broken down into amino acids which then release ammonia as an end product. Ammonia is converted to urea in the liver. Urea is removed by the kidneys. Similarly the proteins especially animal proteins produce acids which are excreted by the kidneys. Hence when kidneys are diseased the blood urea levels go up and acid accumulation takes place in the body.
The second important function of the kidney is to maintain the internal environment of the body (i.e) the acid-base and electrolyte of water and it is the responsibility of the kidneys to correctly remove the exact quantity so that we are neither dehydrated nor swollen up. Similarly we take lot of salt in our diet (which is sodium chloride) to improve the taste of food and it becomes the duty of the kidneys to remove this extra salt so that we do not get high blood pressure. Various minerals including potassium are found in natural foods which again are excreted by the kidneys.
Historically the first diet that was recommended for patients with kidney failure was rice potato diet which was based on the concept that proteins should be avoided to the maximum and the patients should get energy from carbohydrates. This would then result in less production of urea. Similarly barley was promoted as an important food since it is purely a carbohydrate. Subsequently, the 20gm protein including vegetable and animal proteins.
The biggest drawback of all the above diet was that the urea levels came down but patients became under nourished and the quality of life suffered. Hence, the present concept where protein restrictions mainly holds for the western diet to about 40-50 gms per day. The vegetarian diet does not contain large protein to be restricted. So average Indian vegetarian diet is more or less tailor made with regards to the protein intake in patients with kidney failure. It is also important to differentiate whether patients suffer from acute or chronic kidney failure. In acute kidney failure where there is temporary cessation of kidney function, nutrition is very important for the recovery of the patient. Hence protein restriction is not advocated. Whereas in chronic renal failure where the kidneys are irreversibly damaged protein reduction to 40 gms per day especially avoidance of animal protein is advocated early in the disease to prevent progression. When the disease is advanced, protein restriction is not recommended since patients will become under nourished.
Coming to the salt intake, salt is sodium chloride and not urea as confused by lay people. All patients with kidney disease do not require salt restriction. Only those who have swollen legs require salt restriction. Salt substitute are dangerous since they contain potassium.
There is a misconception that large quantities of water will improve kidney function. On the contrary, in patients with kidney failure, water accumulates in the body resulting in hyponatremia. Hence water or fluid restriction is important which will vary from patient to patient.
Almost all patients with kidney failure require potassium restriction in the diet. High potassium is found in fruit juices, coconut water, dried fruits, red meat, etc.
Coming to patients with kidney stone, again there is change in the concept of diet. Originally since majority of the stones are calcium oxalate stones, low calcium and oxalate diet were recommended. However it has been shown that restriction of calcium on the contrary leads to loss of calcium in bones and continuation of stone formation and hence low calcium diet is not advised. Similarly tomatoes have become notoriously responsible for stone formation which is not correct. What has been found out is that the high protein in the diet leads to uric acid formation and highly acidic urine. This in turn precipitates stone formation. Also high salt in the diet drags the calcium along with sodium in the urine resulting in stone formation. Hence the present recommendation is low protein and low salt diet for patients with kidney stones. Similarly, acidic urine results in burning especially when there is urinary tract infection. The diet with large quantities of vegetables makes the urine alkaline and relieves the symptoms.
- Madras Institute Of Nephrology, Chennai, India