Overview

Kidney disease is a long-term condition characterised by an abnormality in the structure or function of the kidneys.¹ The disease results in reduced kidney function over time, until eventually, they may stop working. Treatment therefore requires a specialised, personalised care plan to prevent complications.

Medical nutrition therapy can be an effective tool to halt the progression of kidney disease through tailored dietary changes. This dietary approach may prevent the need for more invasive treatment, such as transplantation if your kidneys fail. Let’s explore this intersection of nutrition and medicine, and unravel the dietary changes that can guide patients towards optimal health. 

What are the kidneys?

The kidneys are two bean-shaped organs located below your ribcage, at the back of your abdomen. As part of the renal system, they perform many important functions in maintaining homeostasis, such as balancing fluids in the body and producing urine as a by-product. The kidneys function by filtering out substances from your blood and returning important substances through reabsorption. By eliminating waste and excess fluid, your kidneys maintain a healthy balance of water, salts, and minerals within your bloodstream. 

Waste substances and excess water are filtered out of the bloodstream via your kidneys to form urine, which is passed out through your ureters and into your bladder to be stored until urination.² This process fine-tunes the amount of fluid, toxins, waste products, protein, sugars, and electrolytes in the blood.³

The kidneys are also involved in processes beyond filtering the blood. These include:

• Controlling the acidity of the blood so to maintain a stable pH
• Regulating blood pressure
• Stimulating the production of red blood cells
• Activating vitamin D (which is necessary for bone health)

What is kidney disease?

Kidney disease is characterised by a gradual loss of the normal function of the kidneys. A combination of issues can put a strain on the kidneys and lead to the development of chronic kidney disease, such as:

• High blood pressure (hypertension)
• Uncontrolled type 1 and type 2 diabetes
• Kidney inflammation and infections
• Genetic factors
• Blockages (e.g., kidney stones)

Therefore, lifestyle changes to lower blood pressure and control underlying conditions can help to prevent kidney disease.^4,5 There may be no symptoms of kidney disease in the early stages of the disease. At later stages, patients may notice symptoms such as:¹

• Blood in the urine
• Foamy urine
• Needing to urinate during the night
• Decreased urination
• One-sided pain of the back or abdomen

As the disease progresses, more noticeable symptoms will develop, including:¹

• Fatigue
• Nausea and vomiting
• Metallic taste in the mouth
• Swollen ankles, feet or hands (oedema)
• Weight loss and poor appetite
• Itchy skin
• Shortness of breath

Prompt diagnosis of kidney disease is important to prevent its rapid progression. See your GP if you have persistent or concerning symptoms that could be caused by kidney disease.

Progression 

Chronic kidney disease is progressive, meaning it gets worse over time. At diagnosis, you may be given a stage to describe the point of progression of your condition. No matter the stage of kidney disease you are at, the main goal of therapy is to halt the deceleration in kidney function and prevent kidney damage from causing complications.

Stage 1 - Mild loss of function

Kidneys can still function well and kidney disease is unlikely to be diagnosed at this stage.

Stage 2 - Mild kidney damage

Kidneys may have a slightly reduced function, but you may still not have symptoms.

Stage 3 - Moderate kidney damage

Kidneys are no longer working as they should. This leads to a build-up of waste and fluid in the blood and causes other problems such as raised blood pressure, fatigue, and oedema.

Stage 4 - Severe kidney damage

In the last stage before kidney failure, the kidneys have very limited function. Symptoms will be more obvious and can disrupt daily life.

Stage 5 - Kidney failure

The kidneys stop working, causing waste and fluid to build up in the body and you may become very ill and experience other health issues.⁶

Complications 

Kidney disease can cause a range of complications linked to mortality and poor quality of life, which worsen in severity as kidney function reduces. Complications may include:⁷

• High blood pressure
• High cholesterol
• Anaemia
• Bone disease (e.g. renal osteodystrophy)
• Water retention
• Electrolyte imbalances

Treatment

While kidney disease only progresses to kidney failure in 2% of patients, it is crucial to prevent this progression as at this stage there are limited treatment options available, and dialysis and renal transplants are required.

Dialysis involves attending several hour-long appointments, three times a week (or potentially daily), to filter the blood using a machine that does the job of the kidneys. This treatment can therefore significantly affect your day-to-day life. 

While it may be preferable to have a kidney transplant to receive a functional kidney from a donor, the number of patients with end-stage kidney disease far exceeds the supply of organs available, so many patients wait several years before receiving a transplant.⁸ 

Impact on nutrition

Kidney disease can impact nutrition since the kidneys are crucial in the maintenance of the balance of electrolytes such as potassium, sodium, and phosphorus, which are found in many foods. If your diet is not controlled, these substances can build up in the bloodstream, causing widespread complications. Furthermore, the digestion of protein produces waste products that are normally filtered out of the bloodstream, but in kidney disease, these waste products can build up.⁹ 

What is medical nutrition therapy?

Medical nutrition therapy is an approach to managing kidney disease. It involves tailoring nutritional needs to the individual and adjusting their diet as the disease progresses to prevent complications and improve quality of life.¹⁰ This involves counselling from a dietician to delay the progression of chronic kidney disease in the early stages and delay the need for dialysis or transplant in the later stages.¹¹ When adhered to by patients, medical nutrition therapy can improve disease outlook and increase life expectancy.¹²

Components of medical nutrition therapy 

Reduce protein intake 

As the kidneys lose their ability to filter blood, patients are advised to modify their diet to help the kidneys maintain a healthy balance of electrolytes and other minerals. Dietary interventions may include reduced protein intake, particularly from animal foods, to prevent the build-up of waste products in the blood. However, for patients on dialysis, the advice may change to consume more protein, since dialysis treatment can remove protein from the blood which must be replaced through the diet.¹³

Maintain correct levels of electrolytes

Electrolytes such as sodium, potassium, and phosphorus can increase in cases of kidney disease, therefore you could be advised to limit foods high in these minerals. Sodium is found in salt and can cause fluid to be retained, leading to high blood pressure, therefore salt consumption may be reduced.

Potassium, found in a range of fruits, vegetables, dairy products, and other foods, must be maintained at the correct level, as levels too high or low can cause heart problems. Tailored medical advice from your healthcare provider will ensure the correct amount of electrolytes is consumed. Phosphorus intake may be controlled by limiting high-protein foods, as this electrolyte can weaken bones.¹⁴

Ensure optimal water intake

You may also be advised to ensure optimal intake of water to prevent the progression of kidney disease.¹⁵ However, consuming too much water can damage the kidneys by putting too much pressure on them. So you must always consult your healthcare professional who will advise the appropriate water intake for you.¹⁶

Low-fat diet

Your dietician may recommend a low-fat diet, because of the risks of cardiovascular complications associated with kidney disease.¹⁷ Certain types of fat, such as saturated and trans fats in animal products, baked goods, fried foods, and margarine, can build up and clog the insides of your blood vessels. Blocked blood vessels can increase your chances of cardiovascular events such as heart attack and stroke. Heart health may be protected by replacing them with monounsaturated and polyunsaturated fats, known as ‘healthier’ fats, found in vegetable oils, nuts and fish. 

Personalised nutrition 

Seeking tailored advice to develop a personalised nutrition plan is crucial to get the most out of medical nutrition therapy. By assessing individual health and current nutritional status, tailored, realistic, and achievable nutrition goals can be set. Having clear, personalised nutrition goals is essential because specific nutritional needs are unique to each patient, and can be affected by the stage of disease, current medical conditions, weight, activity levels, age, gender and medications.¹⁸

Regular checkups are required in medical nutrition therapy to monitor overall health, manage dietary challenges, address nutritional deficiencies or excesses and help you plan balanced meals. Collaboration between healthcare professionals to adjust dietary changes based on laboratory results, blood pressure and other health indicators allows the diet to be modified depending on disease progression. Phosphate binders may be prescribed if the disease worsens to soak up excess phosphorus in the stomach. This is to prevent it from entering the bloodstream, as it may not be removed by the damaged kidneys.¹⁹

Practical tips

• Buy fresh food rather than pre-prepared, packaged food so you can control how much sodium you consume
• Use spices and seasonings instead of salt
• Avoid low sodium salt replacements, which may be high in potassium
• Check nutrition labels on foods to see how much salt and protein they contain 
• Use cooking methods that require less oil than frying, such as baking or boiling
• Trim fat from meat or choose low-fat options such as chicken breast
• Drain canned fruits and vegetables before eating

Challenges

Despite the success of medical nutrition therapy in the management of kidney disease, there are several challenges that this therapy may pose. Patients are often unaware that they have kidney disease, therefore by the time they are diagnosed, it may be too late for the dietary changes to reduce the loss of kidney function. Additionally, doctors may not refer patients to dietitians due to its cost and a lack of expertise and emphasis on dietary interventions among doctors in developing countries. 

Furthermore, not all patients may not have the time or resources to invest in their diet and introduce changes to their daily routine.²⁰ If the diet is not carefully monitored by a dietician, patients may be at risk of micronutrient deficiencies due to inadequate dietary consumption and reduced absorption of nutrients. These losses could include essential micronutrients such as vitamin C and zinc, therefore patients should be carefully monitored throughout treatment, and adjustments made where necessary.²¹

Summary

Chronic kidney disease causes reduced function of the kidneys to filter the blood effectively. It is a progressive disease, with patients advancing through the stages of disease over time, until kidney failure ensues. Medical nutrition therapy can have significant improvements on this rate of decline, and dietary changes can delay the need for medical procedures such as dialysis and transplants.

A collaborative approach between patients and healthcare professionals is needed to develop a personalised nutrition plan and monitor the patient's progression, adapting their diet as necessary. While not a curable condition, medical nutrition therapy can slow disease progression. Medical nutrition therapy can provide the best possible outlook for kidney disease patients when implemented with other lifestyle changes, such as blood pressure management, blood sugar control, smoking cessation, exercise, and medication management.