The function of the kidneys

The kidneys are complex organs that have a number of functions such as regulating blood pressure, fluid balance, red blood cell production, and nutrient and waste balance(1).  Amazingly, this pair of small organs filter approximately 200 quarts or 50 gallons of blood every 24 hours(1).  With normal kidney function, clean blood is sent back to the bloodstream and waste products are sent to the bladder to be excreted in the urine(1). 

What causes contribute to chronic kidney disease?

According to the National Kidney Foundation, Diabetes and Hypertension are responsible for approximately 2/3 of chronic kidney disease cases(1).  Chronic high blood sugar can cause damage to many organs in your body including the kidneys, the heart, blood vessels, nerves, and eyes. High blood pressure puts a similar strain on the walls of your blood vessels and can cause heart attacks, strokes, and chronic kidney disease. Over time, strain on the vessels in the kidneys will hinder their ability to function properly. This condition is known as chronic kidney disease (CKD) and is defined in stages 1-5 based on a person’s level of kidney function.

Nutrients of concern in chronic kidney disease

First, sodium intake should be limited to less than 2,000 mg/day to promote healthy blood pressure(2). This will reduce the strain on the vessels in the kidneys and prevent the progression of kidney disease.

When kidney function is compromised and the kidneys are not filtering at full capacity, levels of nutrients in the blood can rise to dangerous levels. For this reason, it can be important to limit Potassium and Phosphorus in the diet to keep blood levels normal and prevent complications.

• Potassium is important for nerve function, muscle contraction, and heart function. However, high blood potassium levels can cause irregular heartbeats which can be fatal (3).  Low potassium can cause muscle weakness and cramps (3). If the kidneys can no longer balance the potassium in your blood, dietary potassium will have to be adjusted to promote normal potassium levels. 

• Phosphorus plays an important role in bone health, but high blood phosphorus levels can cause calcium to be pulled from the bones and deposited in soft tissues and organs which can lead to osteoporosis, cardiac arrest, and organ dysfunction (3).  The extent of Potassium and Phosphorus restriction will be extremely personalized and will depend on a person’s stage of kidney disease and blood work.

At later stages of CKD, it may be necessary to limit protein and fluid intake (2).  Protein metabolism can strain the vessels in the kidneys and creates waste products that must be cleared from the blood (3).  When kidney function is compromised, protein intake must be limited to prevent the progression of kidney disease and the buildup of waste products in the blood. Fluid intake may also have to be limited to prevent fluid buildup that could have dangerous consequences for the heart and the lungs (3).

The importance of nutrition support for CDK

A renal diet can be challenging to maintain, especially if a person has other chronic conditions that need to be managed such as diabetes. If you are confused, you are not alone! Consider reaching out to a Registered Dietitian who can help you personalize a meal plan that helps to preserve kidney function and fits your lifestyle.

References

1. Chronic Kidney Disease Nutrition Intervention. (n.d.). Adult Nutrition Care Manual. Retrieved March 27, 2022, from https://www.nutritioncaremanual.org/topic.cfm?ncm_category_id=1&lv1=5537&lv2=274796&lv3=274815&ncm_toc_id=274815&ncm_heading=Nutrition%20Care. 
2. Kidney basics. National Kidney Foundation. (2021, March 27). Retrieved March 28, 2022, from https://www.kidney.org/kidney-basics 
3. Mahan, L. K., & Raymond, J. L. (2017). Food & the nutrition care process. Krause’s Food & The Nutrition Care Process. https://doi. org/10.1111/pme, 12679.