CKD, leading to end stage renal disease, is a global health problem and is eventually linked to high risk of cardiovascular disease and mortality. It is associated with major alterations in metabolic function 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.
Furthermore, diabetes mellitus and hypertension often coexist as risk factors of CKD, the increased risk of serious cardiovascular disease is outlined, and that is probably the reason why the majority of CKD patients does not reach the dialysis stage, i.e. higher mortality in pre-dialysis stages.
In an effort to halt high cardiovascular risk and CKD progression, the nephrology community has proposed measures tested in large controlled studies, one of which is nutrition.
When diagnosed with CKD it is crucial to understand the importance of following a kidney-friendly diet, as advised by your nephrologist and /or dietician, as nutrition is a significant part of the treatment plan followed by renal patients and is adjusted according to your CKD stage.
The aim of proposed diets for CKD patients is to retard the progression of renal disease -especially in proteinuric patients- by decreasing protein intake. That is why the NFK recommends 0,6-0,8 gr of protein / kgr body weight when it comes to pre-dialysis CKD diets. This limit is safe, not putting the patient in the danger of malnutrition -which might increase mortality- and most importantly it seems to suffice for the control of deleterious hyperphosphatemia that such patients are prone to.
It is important to note that 50% of protein intake in CKD patients should be of high biological value, for example egg whites.
Also, patients with renal impairment progressively lose the ability to excrete phosphorus, which carries the risk of endovascular calcifications and eventually of higher mortality.
Phosphorus intake is directly linked to protein intake. Lately, it has been found that its absorption by the intestine is higher when inorganic. This means that except of lower protein intake, CKD patients should be directed by nephrologists and dieticians to avoid all possible sources of inorganic phosphorus which is contained in food additives and foods with conservatives, such as fast food.
Furthermore, the organic phosphorus of animals and plants is highly recommended as it is less absorbed by the intestines (40%).
The nephrology community has proposed the introduction of the phosphorus /protein content in food labels, so that patients can be aware of the ph /protein load of all foods.
Renal patients more often than not suffer from diabetes or hypertension, which eventually lead to CKD. Therefore, it should be noted that close monitoring of patients’ metabolic disturbance - cofactors is essential, like glucose control in diabetes and sodium intake in hypertension.
CKD patients are more prone to hypoglycemia and thus their insulin dose must be adjusted as insulin is excreted by the kidneys in CKD. Adjustment of the patient’s overall diet according to patient evaluation and needs is also crucial. The same attention should be paid in sodium intake concerning the decreased ability of the remaining nephrons to control sodium balance, whether it is excess sodium or sodium depletion. Dieticians should also target to the control of water electrolyte balance and blood pressure.
Control of calorie intake is also fundamental in order for renal patients to avoid the risk of malnutrition and uremic anorexia (at more advanced stages of CKD). The proposed caloric amount for patients at a pre-dialysis stage must be about 30Kcal/kg of body weight.
Another issue that has gained interest lately in the era of CKD diet is the supplementation of bicarbonate and possible nutrition supplements containing high biological calories and proteins but less phosphorus.
The former is under investigation because the correction of metabolic acidosis in CKD can possibly retard CKD progression. Of course we are talking about low-dose supplementation of bicarbonate in order to avoid metabolic alkalosis.
Ever since the first dialysis treatment attempts in the early sixties, the key question on nutrition for hemodialysis patients remains a matter of controversy.
Studies have shown that strict dietary restriction orders can pose the risk of malnutrition for dialysis patients, which carries a high risk of mortality as shown by the MIA syndrome (malnutrition, inflammation, acidosis).
Nephrologists, healthcare specialists as well as dieticians suggest a specific diet for end-stage CKD patients, which is slightly different to the diet which is ideal for pre-dialysis patients.
It is important that hemodialysis patients avoid malnutrition yet make up for protein losses through dialysis membranes during hemodialysis procedure. This can be achieved when patients have protein intake of approximately 1gr per kg of body weight (instead of 0,6-0,8 gr per kg of body weight which is recommended to patients in predialysis stages).
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 in CKD and increase cardiovascular risk.
If the above cannot be attained through diet, there are now available special diet supplements that can be prescribed and used only under nephrologist and expert dietician guidance.
Low potassium, sodium and phosphorus intake is crucial when it comes to the nutrition of hemodialysis patients.
A rise of potassium in patients’ serum may put them at serious risk especially on days in-between dialysis sessions. So, patients are advised to follow a potassium restricted diet as recommended by their nephrologist. Education of patients about potassium content in foods is equally important, as they need to make conscious decisions on what kinds of fruits or vegetables they can consume, as well as on the way of food preparation, for example double boiling and extraction of the remaining juice of vegetables, eating a small quantity of foods with high potassium concentration etc.
Minimizing sodium intake and avoiding food additives and fast foods is crucial because it lessens the expansion of the extra vascular volume that occurs in end stage renal disease and causes high blood pressure, cardiac hypertrophy and eventually increased cardiovascular mortality. Water and sodium control in dialysis patients carries a good prognostic result.
Phosphorus control when patients are on dialysis is perhaps one of the most important factors for interventional and rescue manoeuvres in end-stage renal disease diet (ESRD diet). It is essential that patients are educated about the various foods which are rich in phosphorus, such as dairy products, fish, drinks with preservatives like cola drinks, food additives contained in processed foods etc.
High phosphorus balance increases mortality of dialysis patients both directly and indirectly by co-acting in secondary parathyroid hormone dysregulation. Phosphorus lowering drugs, special dialysis modalities or more extended dialysis can be used in order to reverse this positive balance. Ηemodialysis 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 and thus only a combination of dialysis, drugs and diet can be used to control hyperphosphatemia. However, special attention should be paid so that the patient does not run the risk of malnutrition due to extremely low protein intake. It should be taken into account that excess fat should also be avoided by ESRD patients and generally their diet should suit the altered metabolic control of these patients.