CKD, leading to end-stage renal disease, is a global health problem. It is associated with major metabolic function alterations because of the accumulation of uremic toxins, metabolic acidosis, abnormalities of lipid, mineral and bone metabolism, insulin resistance, anemia, vitamin D deficiency, skeletal muscle dysfunction, and many others.
The heavily caloric diet of the Western world, characterized by high animal protein and low fruit and vegetable intake, has propelled the growth of all chronic diseases, including CKD. This nutrient combination leads to a high net endogenous acid production which requires the kidneys to work more in order to prevent acidosis. The high animal protein intake also interferes with glomerulus’ ability to protect itself from blood pressure changes.
Many patients affected with CKD are mostly concerned about kidney failure and dialysis, but due to the elevated risk of cardiovascular disease which accompanies this disease, the great majority will not live long enough to need renal replacement therapy.
In an effort to halt high cardiovascular risk and CKD progression, one of the proposed measures from the nephrology community is a change in nutrition.
Nutrition is a significant part of the treatment plan, so it is crucial to understand the importance of following a kidney-friendly diet advised by your nephrologist and/or dietitian when diagnosed with CKD. The right nutrition plan will help you control your blood pressure (and diabetes, if affected) and is adjusted according to your CKD stage, body size, symptoms, age, activity level and other health conditions.
Protein is one of the main components needed for our body to grow, heal and stay healthy. Having too little or too much protein can be a problem. To stay healthy and help you feel your best, you may need to adjust how much protein you eat.
The suggested intake of protein depends on our body size, activity level and health concerns. The aim of a CKD diet is to delay the progression of renal disease by decreasing protein intake, especially in proteinuric patients. When it comes to pre-dialysis CKD diet, the National Kidney Foundation (NKF) recommends 0,6 - 0,8 g of protein per kg of body weight.
It is important to note that 50% of protein intake in CKD patients should be of high biological value, for example egg whites.
As kidneys become less effective at filtering waste products, they lose the ability to excrete phosphorus so the blood phosphate level rises. When this happens, calcium is drawn from the bones, which carries the risk of endovascular calcifications and eventually, a higher mortal probability.
Phosphorus intake is directly linked to protein intake. Lately, studies have shown a higher intestine absorption for inorganic phosphorus. This means that, except for lower protein intake, CKD patients should be advised to avoid all possible sources of inorganic phosphorus which are found in food additives and foods with conservatives, such as fast food. Furthermore, the organic phosphorus found in animal and plant produce is strongly recommended, as it is less absorbed by the intestines (40%).
The nephrology community has proposed the introduction of the phosphorus and protein content in food labels, so that patients can be aware of the load in all edible products.
More often than not, renal patients suffer from diabetes or hypertension. Therefore, close monitoring of patients’ metabolic disturbance cofactors, like glucose control in diabetes and sodium intake in hypertension, is essential.
Patients with CKD are also more prone to hypoglycemia or low blood sugar, so their insulin dose must be carefully adjusted.
The same attention should be paid to sodium intake because of the nephrons’ decreased ability to control sodium balance, whether it be its excess or depletion. Even if salt is not added during cooking, sodium can still be found in other food sources especially in packaged and processed foods. Sodium absorbs fluid, makes us feel thirsty and drink more. As a result, the weight gain from fluid rises which increases blood pressure.
Control of calorie intake is also fundamental in order for renal patients to avoid the risk of malnutrition and uremic anorexia (which can occur in more advanced stages of CKD). The proposed caloric amount for patients at a pre-dialysis stage must be about 30kcal per kg of body weight.
Ever since the first treatment attempts in the early sixties, the key question of nutrition for hemodialysis patients has remained a matter of controversy. Studies have shown that strict dietary restrictions can pose the risk of malnutrition for dialysis patients, which then increases the risk of a higher mortality as shown by the MIA syndrome (malnutrition, inflammation, acidosis).
Nephrologists, healthcare specialists as well as dieticians will suggest a specific diet for end-stage CKD patients, that slightly differs from the pre-dialysis diet.
It is important for hemodialysis patients to make up for protein losses during dialysis procedure, while avoiding malnutrition. This can be achieved with a protein intake of approximately 1g per kg of body weight (instead of 0,6 - 0,8 g per kg of body weight).
The proteins received should be of high biological value in order for patients to avoid positive phosphorus balance and high lipid content. Such a case would worsen cholesterol-triglycerides abnormalities of renal failure, which act in synergy with other non-traditional atherogenic factors, and increase cardiovascular risk.
If the above cannot be attained through diet, special diet supplements are now available that can be prescribed and used only under nephrologist and expert dietician guidance.
When it comes to the nutrition of hemodialysis patients, low potassium, sodium and phosphorus intake is crucial.
Potassium is a mineral that controls nerve and muscle function, helps your heart beat normally and maintains pH level and fluid and electrolyte balance. A rise of potassium in patients’ serum may put them at serious risk especially on days in-between dialysis sessions. When you have ESRD, phosphorus can build up in your blood, slow your pulse and cause nausea, weakness and numbness.
Educating yourself about potassium content in foods is equally important, as you will need to make conscious decisions on what kinds of fruits or vegetables you can consume, how to prepare your food (e.g. double boiling and extraction of the remaining juice of vegetables), determine which foods with high potassium you can eat in small quantities etc.
Minimizing sodium intake and avoiding food additives and fast foods is important because it lowers the increase of blood volume that occurs in ESRD and causes high blood pressure, thickening of the heart muscle (cardiac hypertrophy) and even increased cardiovascular mortality. A good prognostic result can be attained with a controlled intake of water and sodium.
Phosphorus is an essential mineral that works with calcium and vitamin D to keep your bones and tissue healthy. When you are on dialysis, phosphorus can build up in your blood and lead to bone disease or calcification of tissues in the heart, arteries, joints, skin or lungs. It can also increase mortality indirectly, co-acting with secondary hyperparathyroidism (or excess of PTH in the bloodstream due to overactivity of enlarged parathyroid glands). Phosphorus control is probably one of the most important factors determiners of a successful end-stage renal disease diet (ESRD diet). It is essential for you to learn about various foods which are rich in phosphorus, such as dairy products, fish, drinks with preservatives (like cola), food additives present in processed foods etc.
Hemodialysis patients with high protein intake also run the risk of positive phosphorus balance, as phosphorus is a constitutional part of all proteins. Even the daily dialysis schedule cannot clear more than 500-700mg of phosphorus per session, so the only way to control hyperphosphatemia is through a combination of dialysis, drugs and diet.
It should be taken into account that ESRD patients should also avoid excess fat intake and that their diet should suit the altered metabolic control.