Is Fish Bad for Your Kidneys?

Compared with red and processed meat, fish provides high-quality protein with:

• Lower dietary acid load — slower CKD progression in observational studies.
• Less saturated fat — better cardiovascular profile.
• Omega-3 EPA/DHA in oily varieties — lower triglycerides, modest BP reduction, reduced cardiovascular events.
• No additive phosphate (unlike processed deli meats).

For CKD patients — who have cardiovascular disease as the leading cause of death — these are meaningful advantages.

Per 120 g cooked portion:

• Cod — ~ 360 mg potassium / 240 mg phosphate / ~ 25 g protein
• Haddock — ~ 350 mg K / 240 mg P
• Plaice — ~ 320 mg K / 215 mg P
• Lemon sole — ~ 310 mg K / 200 mg P
• Pollock — ~ 380 mg K / 250 mg P

White fish is the lowest-phosphate animal protein commonly eaten in the UK. Steamed, baked or pan-fried (not battered) is the kidney-friendly format.

Per 120 g cooked portion:

• Salmon — ~ 420 mg K / 280 mg P / ~ 2.5 g omega-3
• Mackerel — ~ 380 mg K / 280 mg P / ~ 3.0 g omega-3
• Sardines (tinned, drained) — ~ 480 mg K / 490 mg P / ~ 1.8 g omega-3 (and useful calcium from bones)
• Trout — ~ 430 mg K / 280 mg P / ~ 1.5 g omega-3
• Pilchards — ~ 470 mg K / 460 mg P

For most CKD patients, 1 oily fish portion/week is appropriate. People on dialysis or with raised phosphate may prefer white fish more often and oily fish less often — discuss with your renal dietitian.

These are commonly eaten in the UK and are usually very high in salt:

• Smoked salmon — ~ 3.5 g salt/100 g
• Smoked mackerel — ~ 1.8 g salt/100 g
• Kippers — ~ 2.0 g salt/100 g
• Anchovies — ~ 8 g salt/100 g (use sparingly as a seasoning, not a portion)
• Salt cod (bacalao) — very high; soak overnight before use
• Tinned tuna in brine — ~ 0.9 g salt/100 g (choose 'in spring water' instead)
• Tinned sardines/mackerel in tomato sauce — typically ~ 0.7 g salt/100 g

NHS adult salt target is < 6 g/day; CKD patients with hypertension often aim for < 5 g.

• 2 portions of fish/week including 1 oily — NHS guidance, applies to most CKD patients.
• White fish is the lowest-mineral animal protein — useful when other meal components (e.g. potatoes, tomato sauce) are higher in potassium.
• Tinned tuna/salmon in spring water is a quick, cheap, kidney-friendly lunch protein.
• Avoid breaded/battered/deep-fried — these add salt and refined carbs.
• Mercury: stick to FSA guidance — adults limit shark, swordfish, marlin and large tuna to ≤ 1 portion/week; pregnant women avoid.
• If you take a fish-oil supplement for triglycerides, choose one with no added potassium or magnesium and discuss dose with your team.