Your kidneys do remarkable work. Every day, they filter roughly 200 litres of blood, removing waste products, balancing fluid and electrolytes, and regulating blood pressure (National Kidney Foundation, 2023). When kidney function is reduced, whether from chronic kidney disease (CKD), diabetes, high blood pressure, or other conditions, what you eat becomes an important tool for slowing progression and protecting your kidney function.

Nutrition to support kidney health or CKD is one of the more nuanced areas of dietetics. This is one of the most important areas to seek individual counselling and dietetic support. However, this article will provide a general introduction and introduce a few basic concepts.

What Is Chronic Kidney Disease, and What Does It Have to Do with Food?

Chronic kidney disease (CKD) is a condition in which the kidneys are damaged or not functioning as well as they should, over a period of three months or more. It is classified in five stages based on GFR (glomerular filtration rate), a measure of how well the kidneys are filtering blood (Kidney Disease: Improving Global Outcomes, KDIGO guidelines, 2022).

CKD is fairly common and often develops alongside Type 2 Diabetes and hypertension, which are the two most common causes in Canada (Kidney Foundation of Canada).

Kidneys filter what is in the blood, and nutrition can impact how hard they work.  When kidneys are not functioning optimally, certain substances, including potassium, phosphorus, and sodium, can accumulate in the blood to dangerous levels and affect heart function, bone health, and overall wellbeing.

So Why Does Nutrition Matter?

Dietary management is one of the most effective strategies for slowing CKD progression and reducing complications (Kalantar-Zadeh & Fouque, 2017). What you eat can affect:

• The workload on the kidneys

• The amount of potassium and phosphorus in the blood (which you want to minimize!)

• Blood pressure, which directly affects the rate of kidney function decline

• Your risk of developing cardiovascular disease, which is the leading cause of death in people with CKD

• Overall nutritional status, since CKD is associated with increased risk of malnutrition

The specific dietary approach depends heavily on the stage of CKD and your individual lab values. What follows are general principles that apply broadly, but always confirm recommendations with your nephrology team and dietitian.

What Can You Do?

Strategy #1: Manage Sodium Intake

Sodium causes fluid retention and raises blood pressure, both of which accelerate kidney damage. For most people with CKD, limiting sodium to 2,000 mg per day or less is recommended (KDIGO guidelines, 2022).

Most sodium in the Canadian diet comes from processed, packaged, and restaurant foods, not the salt shaker.

Tip: Read labels on packaged foods and look for options with 5% Daily Value (%DV) or less of sodium per serving (or 120 mg or less per serving). Cooking at home more often and seasoning with herbs, lemon, and spices rather than salt can meaningfully reduce daily intake.

Strategy #2: Understand Protein

Protein management in CKD is nuanced and stage-dependent. In the earlier stages of CKD (stages 1 to 3), very high protein intake (above 1.3 g/kg/day) may accelerate kidney damage, and a moderate intake is generally recommended (KDIGO guidelines, 2022). In later stages or in people on dialysis, protein needs may actually increase.

This is one area where individualized guidance from a registered dietitian is essential. Do not make significant changes to your protein intake without discussing it with your healthcare team.

Tip: Discuss your protein needs with your healthcare team. Your protein needs should be calibrated to your specific stage and lab values.

Strategy #3: Be Aware of Potassium

Potassium is a mineral that the kidneys normally regulate. When kidney function declines, potassium can build up in the blood (a condition called hyperkalemia), which can affect heart rhythm.

Whether you need to limit potassium depends on your lab values and CKD stage. Not everyone with CKD needs a low-potassium diet, particularly in earlier stages.

Higher-potassium foods include: bananas, oranges, potatoes, tomatoes, dairy, beans, and avocados. If your potassium levels are elevated, your healthcare team will likely advise on specific limits.

Tip: Ask your healthcare provider what your most recent potassium lab value was and whether it is within the normal range. This determines whether potassium restriction is relevant for you right now.

Strategy #4: Be Mindful of Phosphorus

Phosphorus is another mineral the kidneys regulate. When kidney function is reduced, phosphorus can accumulate in the blood, contributing to bone disease and cardiovascular complications. Phosphorus is found in protein-rich foods, dairy, nuts, seeds, and whole grains, and is also added to many processed foods in the form of phosphate additives (which are more readily absorbed than naturally occurring phosphorus).

Limiting phosphate additives found in processed and fast food is generally beneficial for anyone with CKD. Whether further dietary phosphorus restriction is needed depends on lab values and disease stage.

Tip: Check ingredient lists for phosphate additives (ingredients containing the word "phosphate," such as disodium phosphate or sodium phosphate). These are found commonly in processed meats, cola drinks, and some packaged foods, and are worth reducing even in early CKD.

Strategy #5: Focus on Heart-Healthy Eating

Cardiovascular disease is the leading cause of death in people with CKD, and many of the dietary strategies that protect the kidneys also protect the heart (Kidney Foundation of Canada). A dietary pattern rich in vegetables, legumes, whole grains, and fish, while lower in sodium, processed meats, and ultra-processed foods, supports both.

Tip: Although a heart-healthy diet is “healthy”, it may sometimes be high in potassium. If you have a potassium-restricted diet, make sure you get a list of fruits and veggies that are lower in potassium. 

The Bottom Line

Kidney nutrition is one of the more individualized areas of dietetics. General principles may apply, but the specific targets that are right for you depend on your kidney function, lab values, and health history. The most important first step is connecting with a registered dietitian who specializes in renal nutrition to build a plan tailored to your situation.

If you are looking for guidance that goes beyond a list of foods to avoid, our dietitians are here to help.