Can I eat fish if I have high potassium?

November 17, 2025 •

4 min read

According to the National Kidney Foundation, the amount of potassium in fish varies significantly depending on the species. This is crucial for anyone managing hyperkalemia, or high potassium, as the kidneys' ability to filter minerals may be compromised. Understanding which fish are low in potassium and how to prepare them is key to safely including this nutritious protein source in your diet.

Quick Summary

The ability to consume fish with high potassium depends on the fish type and serving size. While some fish are naturally higher in potassium, certain varieties and preparation methods make them suitable for a low-potassium diet. Careful selection and portion control are essential for managing mineral intake.

Key Points

Consult a Professional: Always talk to a doctor or renal dietitian for personalized dietary advice when you have high potassium, as needs change with kidney function.
Choose Low-Potassium Fish: Opt for lower-potassium varieties such as flounder, sole, catfish, and shellfish like shrimp and clams.
Limit High-Potassium Fish: Be cautious with or limit intake of high-potassium fish like mackerel, halibut, and salmon, controlling portion sizes strictly.
Control Portion Sizes: Stick to small serving sizes, typically about 3 ounces, to manage overall potassium intake, even with lower-potassium options.
Drain and Rinse Canned Fish: For canned fish like tuna, drain the liquid and rinse to reduce both sodium and potassium content.
Avoid Salt Substitutes: Do not use salt substitutes, which often contain potassium chloride, and season with herbs, spices, and lemon instead.
Prioritize Freshness: Choose fresh, unprocessed fish over processed or frozen options, which can be high in added sodium and phosphorus.

Understanding Potassium and Hyperkalemia

Potassium is a vital mineral that plays a critical role in nerve function, muscle contraction, and maintaining a regular heartbeat. For individuals with healthy kidneys, the body regulates potassium levels by excreting excess amounts through urine. However, for those with impaired kidney function, this process is less efficient, leading to a build-up of potassium in the blood, a condition known as hyperkalemia. Untreated hyperkalemia can cause serious health issues, including irregular heartbeats, nausea, and muscle weakness. Therefore, dietary management, including careful fish selection, is a cornerstone of treatment.

Fish is a high-quality protein and a rich source of omega-3 fatty acids, which are beneficial for heart health. However, as the potassium content varies widely between species, not all fish are suitable for a low-potassium diet. The key is moderation and making informed choices based on the potassium levels of specific fish types and paying close attention to portion sizes, which are typically recommended at about 3 ounces.

High-Potassium vs. Low-Potassium Fish

When managing potassium intake, it is important to distinguish between fish that are high in this mineral and those that are low. High-potassium fish, while nutritious, can be problematic in large quantities. In contrast, low-potassium fish can be enjoyed more regularly with proper portion control.

High-Potassium Fish

Fish species such as halibut, mackerel, and certain types of tuna contain significant levels of potassium. For example, some sources indicate halibut can contain as much as 549 mg of potassium per 100g serving, and mackerel contains 558 mg per 100g. Even salmon, celebrated for its omega-3 content, is considered moderately high in potassium. While these fish can offer health benefits, they should be consumed in very limited quantities, if at all, depending on a person's individual dietary restrictions. Canned fish, especially those with bones like sardines, can also be high in phosphorus, which is another mineral that often needs to be managed on a renal diet.

Low-Potassium Fish and Shellfish

Fortunately, there are many delicious fish and shellfish options that are lower in potassium. These include flounder, sole, catfish, and certain shellfish varieties.

Flounder and Sole: Cooked flounder or sole contains about 167 mg of potassium per 3-ounce portion.
Canned Light Tuna: Canned light tuna, when packed in water and drained, is a good low-potassium choice. A 100g serving contains approximately 176 mg of potassium. Rinsing canned tuna can further reduce the sodium content.
Shrimp: A 100g serving of shrimp has only around 101 milligrams of potassium, making it an excellent option.
Oysters and Clams: These shellfish are also low in potassium, with clams containing as little as 58 mg per 100g.

Comparison of Fish Potassium Content


Fish Type	Potassium per 100g cooked (3.5oz)	Category	Notes
Mackerel	558 mg	High	High in Omega-3s; limit intake.
Halibut	549 mg	High	Limit intake due to high potassium.
Salmon	439 mg	Moderate-High	High in Omega-3s; small portions.
Black Cod	459 mg	Moderate-High	Omega-3 rich; mind portion size.
Haddock	351 mg	Moderate	Moderate potassium; watch portion.
Bluefin Tuna	323 mg	Moderate	Higher potassium than canned light tuna.
Canned Light Tuna	176 mg	Low	Drain and rinse to reduce potassium and sodium.
Flounder/Sole	197 mg	Low	Lower in potassium, good option.
Shrimp	101 mg	Very Low	Excellent low-potassium choice.
Clams	58 mg	Very Low	Excellent low-potassium choice.

Preparing Fish for a Low-Potassium Diet

Preparation methods can also influence the total potassium and sodium intake. For canned fish like tuna, draining and rinsing the fish can significantly reduce the sodium content. Choosing fresh, unprocessed fish over processed or frozen varieties is often better as they typically have lower sodium levels. When seasoning fish, rely on herbs, spices, lemon juice, and pepper instead of salt substitutes, which often contain potassium chloride and are not recommended for those with hyperkalemia. Baking, grilling, or poaching fish are healthy cooking methods that don't require adding high-sodium marinades.

The Role of a Renal Dietitian

It is crucial to work with a healthcare provider or a registered renal dietitian to determine the appropriate potassium intake for your specific condition. They can provide personalized advice based on your kidney function and other health factors. As your kidney disease progresses, your dietary needs may change, making regular consultation with a professional essential for effective management. For further guidance and resources, the National Kidney Foundation is an excellent starting point.

Conclusion: Making Informed Choices

Managing high potassium levels while enjoying a healthy diet requires attention to detail, but it doesn't mean giving up fish entirely. By selecting lower-potassium fish like flounder, canned light tuna, or shrimp, and controlling your portion sizes, you can continue to reap the benefits of this heart-healthy protein. Always prioritize fresh, unprocessed fish and use creative, low-sodium seasoning techniques. Your renal dietitian is your best resource for creating a balanced and safe meal plan that fits your individual needs and supports your kidney health. By being mindful of your choices, you can navigate your diet with confidence and enjoy a variety of foods safely.

Frequently Asked Questions

Some of the lowest potassium fish and seafood options include clams, shrimp, oysters, and flounder. For instance, a 100g serving of clams can contain as little as 58mg of potassium.

Yes, canned light tuna can be a good option. To reduce its potassium and sodium content, choose a low-sodium variety packed in water, drain the liquid, and rinse the tuna thoroughly before eating.

Fatty fish like salmon are naturally moderate to high in potassium, so they should be consumed in smaller, controlled portions if you have hyperkalemia. It is best to discuss your individual limits with a dietitian.

No, you should not use salt substitutes. Many of these products replace sodium with potassium chloride, which can significantly increase your potassium intake. Use herbs, spices, and lemon for seasoning instead.

Baking, grilling, or poaching fresh, unprocessed fish are the best cooking methods. Avoid fried fish, as pre-prepared versions can have high levels of added sodium and phosphorus.

You don't necessarily have to avoid all fish with high potassium, but you must strictly limit your intake and portion size. Consulting a renal dietitian is the best way to determine if and how you can safely include them in your meal plan.

For individuals managing hyperkalemia, a general guideline is to limit fish servings to about 3 ounces, or the size of a deck of cards, one to two times per week. A dietitian can help set a more precise limit.