Food with a moderate dietary supply of protein and phosphate is important in conservative CKD treatment.
In order to prevent progression in the best way possible, the following are the aims of dietetic treatment at the pre-terminal kidney disease stage:
• Minimisation of uraemic intoxication
• Delay in progression
• Avoiding malnutrition and muscle catabolism
• Early reaction to any possible life-threatening electrolyte metabolic disorders such as hyperkalaemia.
• Early reaction to problems in the calcium-phosphate metabolism with induction of renal osteopathy
• Maintaining an optimum nutritional status
Various prospective studies and meta-analyses show that a reduction of the protein content in the diet can delay the final stage of kidney disease and the start of dialysis. In addition, a low-protein diet reduces the accumulation of uremic toxins and phosphate. (Cianciaruso et al. 2008; Fouque and Laville 2009; Bernhard et al. 2001)
According to the K/DOQI guidelines on the treatment of CKD, the recommended dietary protein supply for CKD patients is slightly lower than for the general population at 0.7 g/kg ideal weight compared with 0.8 g/kg. An appropriate energy supply is important for nephropathy patients in order to avoid malnutrition.
|Protein:||0.7 g/kg ideal weight (75% with high biological value)|
|Carbohydrates:||60% of calories (preferably complex sugars)|
|Lipids:||30% of calories/ratio multiple unsaturated:saturated fatty acids > 1.2; cholesterol 300–350 mg/day|
|Calories:||> 35 kcal/kg ideal weight/day for patients < 60 years old; 30 kcal/kg for people > 60 years old|
|Potassium:||Daily consumption for GFR > 10 mL/min|
The effects of diet on the progression of the condition are being discussed by scientists and there is already some controversial data.
Experimental models have provided evidence of a definite nephro-protective effect of the low-protein diet. However, the results obtained in animal testing have not been able to be confirmed in human tests. Numerous studies have already been carried out in this area, but the majority of them have had to be excluded due to poor methodological quality (unchecked studies, too few subjects). None of the remaining studies have been able to confirm that the use of a low-protein diet slows down the progression of kidney disease. However, there has been confirmation of the possibility of controlling uremic parameters and, above all, delaying kidney death and the start of dialysis by years.
The Cochrane meta-analysis from 2006 shows that 16 patients need to be treated with a low-protein diet in order to 'save' one patient per year from kidney death and the start of dialysis. This 'Number Needed to Treat' (NNT) value is even better than was proved in the '4S' study on the effectiveness of statins (NNT=30).
Nutritional status of the CKD patient to be monitored to avoid malnutrition and risk of other disease. CKD patients both on and off a reduced protein diet have been observed to display spontaneous tendencies to reduce their protein and energy intake. In order to prevent this, it is important that their nutritional status (relative weight, % weight loss, BMI, albuminaemia) is regularly monitored by a dietitian.
To date there is no scientific evidence available to define the GFR threshold from which the advantages of a reduced protein diet exceed possible like malnutrition. Before prescribing the diet it is advisable to carry out a comprehensive overall examination of the patient, including the nutritional status, psychological disposition, family environment and socio-economic status of the patient and give the patient thorough information about the aims of the diet.
The term 'low protein' is used for products or diets which supply less protein than normal traditional products or a traditional diet. A reduced protein diet is recommended for kidney or liver diseases and stipulates a daily protein allowance of no more than 50 g. For a healthy person, the recommended daily protein allowance is 0.8 g per kg ideal weight, but the general population consumes an average of around 1.0–1.3g per kg body weight, which is mainly attributed to high meat, sausage and egg consumption. Specially designed low protein products may be used
|Protein supply/day||Low- Protein products||Addition of essential amino acids and ketoanalogues|
|I >90||0.8–1.0 g/kg bodyweight||NO||NO|
|II 60–89||0.8 g/kg bodyweight||NO||NO|
|a. 0.6 g/kg bodyweight||YES||a. Not necessary|
|a. 0.7 g/kg bodyweight||NO||b Not necessary|
|IV 15–29||a. 0.6 g/kg bodyweight||YES||a. Not necessary|
|b. 0.3 – 0.4 g/kg bodyweight||YES||b. 0.1 g/kg bodyweight|
|V <10–15 (not on dialysis)||a.0.6 g/kg bodyweight||YES||a. Not necessary|
|b.0.3 – 0.4 g/kg bodyweight||YES||b. 0.1 g/kg bodyweight
A reduced protein diet of no more than 0.7 g per kg ideal weight per day and phosphate consumption to control the urea and parathormone (the hormone that regulates the level of calcium in the body) levels at the same time may reduce the progression of chronic kidney disease. Protein intake must cover the minimum requirement of essential amino acids (those that the body cannot synthesise) with 75% being of high biological value e.g. eggs, meat, fish, milk, soya and pulses.
With chronic kidney disease, particularly at an advanced stage, the kidneys have a reduced capacity to control potassium which accumulates in the blood. As potassium controls the ability to tense muscles, including the heart muscles, hyperkalaemia can lead to changes in the heart rhythm (arrhythmia) at various levels up to the stopping of the heart. The amounts of potassium supplied vary between 2000 and 3000 mg per day.
Potassium is present in a wide variety of foods including fruit, vegetables, fish and meat. In the event of hyperkalaemia, potassium-rich foods such as ketchup, tinned tomatoes, bran, wholegrain products, muesli, dried fruit, chestnuts, brewer's yeast, pulses, potatoes, chips, spinach, mushrooms and artichokes, olives, bananas, apricots and kiwis, chocolate and cold meat must be limited. Consumption of coffee, tea and wine must also be restricted. Boiling in unsalted water can lead to a loss of 30% of potassium and cooking in two separate lots of water can even double this loss.
With CKD moderate salt intake is important for blood pressure control. The recommended intake is between 1800 to 2500 mg per day (no more than 2g per day added to food) in relation to the stage of development of the disease and the patient's condition.
On average, 25% of the sodium in our diet comes from bread, 50% from table salt and the rest from food. Items that are particularly sodium-rich include, for example, tinned goods, industrial products (pre-cooked, ready meals etc.), cold meat and smoked products, bread and all baked goods, pizza, chips, salted dried fruits, read-made sauces and preserved vegetables, olives, capers and margarine.
In advanced chronic kidney disease, the phosphate break-down in the kidneys decreases, as well as the production of vitamin D (responsible for low amounts of calcium in the blood) and there is an imbalance between the two elements: reduction in calcium and increase in phosphorous. It is beneficial to keep phosphate intake so that it corresponds to both the level of the vitamin D and to that of calcium.
The recommended intake of phosphorous varies between 2000 and 2500 mg per day for CKD patients. It is worth noting that a normal protein (0.8 g/kg protein) diet rarely falls below an intake of 800 mg phosphorous per day.
The presence of phosphorous is mainly linked to protein. It is frequently found in snacks and other ready-made food products. Phosphorous-rich products include bran and wholegrain products, egg pasta or filled pastry products, some cold meat and fish (salmon, sea food), milk and dairy products, brewer's yeast, pulses, dried fruits and cocoa. Tinned goods should be avoided. You must also be aware that white wine contains 74 mg phosphorous per 100 g.
The calorie supply is of great importance, because the toxic condition caused by kidney disease usually leads to a loss of appetite and many patients suffer from malnutrition.
A daily supply of 35 kcal per kg ideal weight is recommended. For patients over the age of 60, 30 kcal per kg ideal weight is advised. The reduction in the protein supply must always be accompanied by an increase in carbohydrate and fat intake.
Ensuring adequate energy intake without increasing the protein and phosphorous intake is a difficult task for dietetic CKD treatment. For this reason, dietetic foods with a low protein content (low-protein) or even with a very low protein content (protein-free) may be used when compiling a diet plan. Thanks to these easily available foods, the patient can:
• reduce the protein supply and therefore save the kidney function
• regulate the calorie supply and therefore maintain the ideal weight
• limit the supply of sodium (in order to control blood pressure) and phosphorous.
Low-protein and protein-free foods are produced using starches and flours with reduced protein, phosphate, potassium and salt content. These foods include pastry products, bread and similar products such as Crackers, Grissini, bread, crispbreads, cakes and biscuits, flours for sweet and savoury recipes, rice, milk and egg substitutes.
Fluid intake must be controlled by the kidneys on the basis of the concentration and dilution of the urine: in the isosthenuric phase, i.e. when the excreted urine has a particularly low weight (between 1010 and 1015), you can drink without restriction; in the hyposthenuric phase, i.e. when the excreted urine is a particular weight below the standard (between 1015 and 1025), this means that there is a slight reduction in the concentration power of the kidneys due to damage, and then the liquid supply will need to be controlled. Frequently, a hydroponic treatment (drink lots) will be proposed to the CKD patient with the aim of increasing diuresis. However excessive liquid supply can lead to hypo-osmolarity, precisely because the sodium supply is often reduced. Therefore patients in the 4th and 5th stage of CKD should generally only consume water in the amounts absolutely necessary to quench thirst.
Compliance is understood to mean the patient keeping to the prescribed treatment. In numerous studies, it has been shown that the main factors which influence compliance in chronic conditions such as kidney diseases are mainly hypertension, diabetes and dyslipidaemia.
Sociodemographic factors do not typically influence a patient's willingness for a prescribed treatment, while understanding and satisfaction play an important role in compliance.
The relationship of the doctor, dietitian and patient with regular monitoring of nutritional status and dietary compliance is important. Clearly explaining the reasons for following the diet in the case of chronic kidney failure can encourage better dietary compliance with consideration to the preferences and eating habits of the patient.