Kidney Disease Diet · What Is It, How It Helps, and More

Kidney disease refers to kidney damage that decreases its function (e.g., the ability to filter waste, such as urea, ions, and excess water from the blood). Most individuals usually do not present with severe symptoms until their kidney disease has progressed. Common symptoms of late-stage kidney disease include fatigue; trouble concentrating; poor appetite; difficulty sleeping; swollen feet and ankles; puffiness around the eyes; dry, itchy skin; or increased frequency of urination, especially at night. If kidney disease progresses,  complications like fluid retention; high blood pressure; fluid accumulation in the lungs (i.e., pulmonary edema); a rise in potassium levels in the blood (i.e., hyperkalemia); or low blood count (i.e., anemia) can occur.

Kidney disease can be classified as either acute or chronic. Acute kidney injury (AKI), also known as acute renal failure (ARF), refers to a sudden and often reversible decrease in kidney function, which involves both injury (i.e., structural damage) and functional impairment. The degree of injury is usually measured by an increased creatinine or decreased urine volume; however, it rarely has a distinct pathophysiology. The pathology can be either identified as pre-renal (e.g., hypovolemia, impaired cardiac function, systemic vasodilation, increased vascular resistance); intrinsic (e.g., renal ischemia, nephrotoxic drugs, infections, vascular diseases); and post-renal (e.g., external and internal obstruction like nephrolithiasis, or prostate hypertrophy).  Renal cellular damage may occur if these pre- or post-renal conditions persist, causing intrinsic renal disease. 

Chronic kidney disease (CKD), on the other hand, is defined by the persistence of kidney damage or an estimated glomerular filtration rate (i.e., eGFR, which evaluates the kidney’s function by calculating the blood filtered by the glomeruli per minute) < 60 ml/min per 1.73 m2, for at least three months. It is a progressive state of kidney function loss due to chronic or persistent damage from conditions such as diabetes mellitus, high blood pressure, recurrent kidney infections, or polycystic kidney disease, eventually resulting in renal replacement therapy (e.g., dialysis or kidney transplantation). 

Treatment of kidney disease depends on each cause and its severity. Individuals may be advised to increase or decrease their intake of water and other fluids; make lifestyle changes to remain as healthy as possible; and adjust their medications according to their needs (e.g., control blood pressure, decrease cholesterol, stop nephrotoxic agents); or treat underlying infections with antibiotics (e.g., ciprofloxacin or co-amoxiclav). In advanced CKD, dialysis or a kidney transplant may be necessary. 

A kidney disease diet, also known as a renal diet, is low in sodium, potassium, phosphorus, and protein and emphasizes the importance of consuming high-quality protein and the correct amount of fluids. An essential step in managing kidney disease involves changes in diet to meet the individual’s needs and maintain a healthy lifestyle. Individuals are strongly advised to prepare foods with minimal salt, keeping their daily intake to less than 2,300 milligrams of sodium. Furthermore, eating the right amount of protein (e.g., 0.6–0.8 g/kg/day for CKD) can also impact kidney health, as eating more protein than necessary may make the kidneys work harder to remove the wastes produced. 

Adjusting the diet is among the first management options for kidney disease. A well-balanced diet affects the quality and quantity of waste filtered by the kidneys by promoting healthy kidney function and slowing the progression of kidney failure. Increased amounts of sodium can harm people with impaired kidney function as their kidneys cannot adequately eliminate excess sodium and fluid from the body. As sodium builds up in the body, fluid may also build up in the tissues and bloodstream, causing edema (i.e., swelling in the legs, hands, and face), hypertension, shortness of breath, and even heart failure. In addition, when kidney function is compromised, the kidney cannot remove excess phosphorus. Elevated phosphorus levels can remove calcium from bones, causing osteoporosis, and can also cause dangerous calcium deposits in the blood vessels, lungs, eyes, and heart. 

Healthy kidneys do not typically have a difficult time filtering proteins. However, damaged kidneys make protein products difficult to filter; therefore, waste products can accumulate in the blood. Protein is essential for tissue maintenance; therefore, eating the recommended amount of protein for the specific stage of kidney disease is important, according to the clinician’s recommendations. 

Lastly, fluid control is important for patients in the later stages of CKD, as increased fluid consumption may cause fluid build-up in the body. Additionally, individuals on dialysis often have decreased urine output, hence increased fluid in the body may put unnecessary pressure on the heart and lungs.

People with kidney disease are advised to consume a diet that includes fresh fruits and vegetables (e.g., apples, peaches, carrots, green beans); low potassium and phosphorus; and moderate amounts of protein. Red bell peppers and berries, for example, are good sources of vitamins, antioxidants, and fiber and are low in potassium, phosphorus, and sodium, thereby acting to protect blood vessels, nerves, and muscles.  In addition, white bread, pasta, rice, wheat cereals, and rice milk are among the kidney-friendly foods suggested for renal diets, as they are lower in potassium and phosphorus. On the other hand, bananas, oranges, potatoes, dairy, and whole wheat bread tend to be avoided for their higher levels of minerals, as mentioned above.