Why potassium control matters in CKD
Potassium is an essential mineral that keeps nerves and muscles working. Healthy kidneys remove excess potassium in urine. In CKD, as kidney function falls, potassium can build up in the blood - a condition called hyperkalaemia.
Mild hyperkalaemia (5.5-6.0 mmol/L) often has no symptoms. Moderate-to-severe levels (> 6.0 mmol/L) can cause dangerous heart rhythm problems. That is why NICE NG203 and KDIGO both recommend regular potassium blood tests and dietary advice as kidney disease advances.
Foods highest in potassium - the league table
These are the foods renal dietitians most often flag for limiting in Stage 4-5 CKD and on dialysis:
- Dried fruit (apricots, raisins, dates, prunes) - potassium is concentrated 4-6x during drying.
- Avocado - very high in potassium; portion control is essential.
- Coconut water - marketed as healthy but can deliver 600+ mg K per glass.
- Banana, plantain - moderate-to-high; often the first fruit patients are asked to limit.
- Potato, sweet potato - very high unless leached (double-boiled).
- Tomato puree, sun-dried tomatoes, tinned tomatoes - concentrated potassium.
- Spinach, chard, beet greens - dark leafy greens are potassium-dense.
- Beans, lentils, chickpeas - nutritious but potassium-dense; portions matter.
- Nuts and seeds - small servings add up quickly.
- Chocolate (especially dark) - moderate potassium plus phosphate concerns.
- Salt substitutes (lo-salt) - pure potassium chloride; avoid completely.
Some standard multivitamins include added potassium salts. Kidney Vitality is formulated without added potassium. See the formulation.
How to keep potassium manageable without a boring diet
The goal is not to eliminate potassium - that would be unhealthy and impossible. The goal is to avoid stacking multiple high-K foods in one meal and to use preparation techniques that reduce potassium:
- Leaching (double-boiling) for potatoes and root vegetables: peel, chop small, soak in warm water for 2+ hours, boil in fresh water, then discard the water. This removes 30-50% of potassium.
- Portion reduction: instead of avoiding banana entirely, have 1/2 small banana and pair it with low-K foods that day.
- Spread potassium across the day: one moderate-K item at breakfast, low-K at lunch, low-K at dinner - rather than three high-K meals.
- Read labels on plant milks and processed foods: some are fortified with potassium; check the 'per 100 g' line.
When you do not need to restrict potassium
Not every CKD patient needs a low-potassium diet. In Stages 1-3 with normal blood potassium, many people eat a normal, balanced diet without restriction. Potassium restriction is mainly for:
- Stage 4-5 CKD (eGFR < 30)
- Patients on dialysis (haemodialysis or peritoneal)
- Those with a history of hyperkalaemia (K > 5.5 mmol/L)
- Patients on ACE inhibitors, ARBs or potassium-sparing diuretics with rising potassium
Your renal team will tell you if and when to limit potassium based on your blood tests, not your stage alone.
What to do if your potassium is high
If a blood test shows high potassium, your team may:
- Review your medications (ACE inhibitors, ARBs, spironolactone, NSAIDs can all raise potassium).
- Check for constipation (potassium is cleared via the gut as well as kidneys).
- Refer you to a renal dietitian for personalised advice.
- In urgent cases, prescribe treatments to lower potassium quickly.
Never stop prescribed medication because of a high potassium result without speaking to your doctor first.
