The major role of the kidneys is to remove waste products and purify blood. Besides this, the kidney plays an important role in removing extra water, minerals and chemicals; it also regulates water and minerals like sodium, potassium, calcium, phosphorus and bicarbonate in the body.
In patients suffering from chronic kidney disease (CKD), regulation of fluids and electrolytes may be deranged. Because of this reason even normal intake of water, common salt or potassium can cause serious disturbances in fluid and electrolyte balance.
To reduce the burden on the kidney with impaired function and to avoid disturbances in fluid and electrolyte balance, patients with chronic kidney disease should modify their diet as per the guidance of the doctor and the dietitian. There is no fixed diet for CKD patients. Each patient is given a different dietary advice depending on clinical status, the stage of kidney failure and other medical problems. Dietary advice needs to be altered for the same patient at different times.
The goals of dietary therapy in CKD patients are to:
- Slow down the progression of chronic kidney disease and to postpone the need for dialysis.
- Reduce the toxic effects of excess urea in the blood.
- Maintain optimal nutritional status and prevent the loss of lean body mass.
- Reduce the risk of fluid and electrolyte disturbances.
- Reduce the risk of cardiovascular disease.
General principles of dietary therapy in CKD patients are:
- Restrict protein intake to <0.8 gm/kg of body weight/day for patients not on dialysis. Patients already on dialysis require an increased amount of protein (1.0 -1.2 gm/kg body weight/day) to replace protein that may be lost during the procedure.
- Supply adequate carbohydrates to provide energy.
- Supply a moderate amount of fats. Cut down the intake of butter, ghee and oil.
- Limit the intake of fluid and water in case of swelling (edema).
- Restrict the amount of sodium, potassium and phosphorus in the diet.
- Supply vitamins and trace elements in adequate amounts. A high fiber diet is recommended.
Details of selection and modification in diet of patients with CKD are as follows:
1. High Calorie Intake
The body needs calories for daily activities and to maintain temperature, growth and adequate body weight. Calories are supplied chiefly by carbohydrates and fats. The usual caloric requirement of CKD patients is 35 - 40 kcal/kg body weight per day. If caloric intake is inadequate, the body utilizes protein to provide calories. This breakdown of protein can lead to harmful effects such as malnutrition and a greater production of waste products. It is thus essential to provide an adequate amount of calories to CKD patients. It is important to calculate the caloric requirement according to a patient’s ideal body weight, and not current weight.
Carbohydrates
Carbohydrates are the primary source of calories for the body. Carbohydrates are found in wheat, cereals, rice, potatoes, fruits and vegetables, sugar, honey, cookies, cakes, sweets and drinks. Diabetics and obese patients need to limit the amount of carbohydrates. It is best to use complex carbohydrates from cereals like whole wheat and unpolished rice which would also provide fiber. These should form a large portion of the carbohydrates in the diet. All other simple sugar containing substances should form not more than 20% of the total carbohydrate intake, especially in diabetic patients. Non-diabetic patients may replace calories from protein with carbohydrates in the form of fruits, pies, cakes, cookies, jelly or honey as long as desserts with chocolate, nuts, or bananas are limited.
Fats
Fats are an important source of calories for the body and provide two times more calories than carbohydrates or proteins. Unsaturated or “good” fats like olive oil, peanut oil, canola oil, safflower oil, sunflower oil, fish and nuts are better than saturated or “bad” fats such as red meat, poultry, whole milk, butter, ghee, cheese, coconut and lard. Patients with CKD should reduce their intake of saturated fats and cholesterol, as these can cause heart disease.
Among the unsaturated fats it is important to pay attention to the proportion of monounsaturated and polyunsaturated fats. Excessive amounts of omega-6 polyunsaturated fatty acids (PUFA) and a very high omega-6/omega-3 ratio is harmful while low omega-6/omega-3 ratio exerts beneficial effects. Mixtures of vegetable oil rather than single oil usage will achieve this purpose. Trans fat containing substances like potato chips, doughnuts, commercially prepared cookies and cakes are potentially harmful and should be avoided.
2. Restrict Protein Intake
Protein is essential for the repair and maintenance of body tissues. It also helps in healing of wounds and fighting against infection. Protein restriction (< 0.8 gm/kg body weight/day) is recommended for CKD patients not on dialysis to reduce the rate of decline in kidney function and delay the need for dialysis and kidney transplantation. Severe protein restriction should be avoided however because of the risk of malnutrition. Poor appetite is common in CKD patients. Poor appetite and strict protein restriction together can lead to poor nutrition, weight loss, lack of energy and reduction in body resistance, which increase the risk of death. Proteins with high biologic value such as animal protein (meat, poultry and fish), eggs and tofu are preferred. High-protein diets (e.g. Atkins diet) should be avoided in CKD patients. Likewise, the use of protein supplements and drugs such as creatine used for muscle development are best avoided unless approved by a physician or dietitian. However, once a patient is on dialysis, protein intake should be increased to 1.0 – 1.2 gm/kg body weight/day to replace the proteins lost during the procedure.