Chronic kidney disease (CKD) is a major risk factor for cardiovascular disease. One in three Australians have risk factors for CKD e.g. hypertension, diabetes, and obesity. It is therefore vital to investigate early, identify and intervene.
If detected and managed in time, deterioration in kidney function can be reduced by as much as 50%. As well as medical management, nutrition therapy provided by a renal dietitian is paramount and has been shown to assist by slowing CKD progression and preventing advancing kidney failure.
In early stages of CKD (1-3a), addressing lifestyle and risk factors such as weight, blood pressure and glycemic control are essential. Promoting healthy eating patterns that include reducing salt, red meat, processed foods, and fats, while increasing fruit, vegetables, omega 3 sources and wholegrains is fundamental.
Over-restricting certain foods (e.g. dietary sources of potassium) at this point is unnecessary and often counterproductive unless clinically needed.
Once patients progress to CKD 3b – 5, a renal dietitian can offer more specific nutritional advice and adapt according to common symptoms. Often patients experience nausea, constipation, fatigue, taste changes and anorexia. Providing education to manage them is vital to slow the progression of disease and prevent malnutrition.
Contrary to popular belief, there is no such thing as the one-size-fits all renal diet. Managing dietary intake in CKD is one of the most complicated diets to treat due to a complex balance of maintaining individual optimal nutritional status, protecting the function of the kidney, responding to biochemical imbalances and managing comorbidities.
Protein, potassium and phosphorus
Protein source is now a key consideration with much research looking at the role of plant-based proteins in CKD. Recent studies have indicated that plant-based proteins when consumed in a varied diet (e.g. Med Diet/DASH) are not only nutritionally adequate but have pleiotropic effects which may favour their use in patients with CKD.
Once CKD is diagnosed, often the first thing a patient is told (or reads) is not to eat bananas, stone fruit, potatoes, avocado, wholegrains, nuts and dairy. They are given lists of foods high in potassium and phosphate (often conflicting) to avoid, regardless of their biochemistry and stage of CKD. I often see patients who have overly restricted their diet based on misinformation given to them and have lost weight, are constipated (lacking fibre) are fed up and no longer have any enjoyment in food.
It is not until a patients eGFR is less than 45mL/min/1.73 m2 that they appear to have impaired potassium tolerance due to reduced kaliuresis. Other factors causing hyperkalaemia should be investigated such as metabolic acidosis and medications (e.g. spironolactone.)
Optimising the carbohydrate content of the meal, especially fibre will impact how potassium is distributed. Dietary fibre not only increases faecal potassium output dramatically, due in part to reduced absorption, but stimulates insulin response and thus potassium uptake into the cells and improves constipation. So, the key message here is to promote the “2 & 5” serves per day of fruit and vegetables and not restrict.
Dietary phosphorus is found in animal-based products (meat, fish, poultry and dairy), plant-based (beans, peas, legumes, cereals, grains, nuts and seeds) and convenience foods with phosphorus containing additives. It is often unnecessarily restricted due to the role of hyperphosphataemia in bone mineral disorders.
Patients are often told to avoid (essential) wholegrains, dairy and nuts. However, the bioavailability of phosphorus is important to consider. Food additives are 90-100% bioavailable whilst animal-based products are 40-60% absorbed and plant-based products 30% (from being bound to phytate).
Studies looking at protein sources of phosphorus showed a vegetarian diet versus meat diet led to lower serum phosphate. A recent Irish study looked at a plant-based diet (pulses, nuts and wholegrains) versus standard diet in dialysis patients. They found both serum phosphate and potassium didn’t change, but variety of foods and fibre both increased significantly.
The benefits of a more plant-based diet are widespread, promoting acid base balance as it generates bicarbonate naturally, reducing severity of hypertension and hyperphosphatemia. It also increases fibre improving glycaemic control and reducing severity of constipation.
Early detection is key, with renal dietetic input and symptom management essential. Instead of limiting wholegrains, fruit, and vegetables, the patient should be encouraged to include a variety of these foods while limiting processed foods. And finally, always keep education simple and consistent.
Key messages
- A renal dietitian can help manage nutritional impact symptoms and slow progression of CKD
- Encourage fruit, vegetables and fibre rich foods
- Prevent over restricting e.g. a low-potassium diet for all is inappropriate.
Author competing interests – nil