Understanding the Alkaline Diet: Is Tuna Considered Acidic?

October 14, 2025 •

4 min read

While foods are often classified as 'acidic' or 'alkaline' based on the residues they leave after digestion, tuna is a key source of lean protein and essential nutrients. So, is tuna considered acidic? The answer is nuanced, depending on whether you are looking at its natural pH, or its effect on the body after digestion, which is determined by its PRAL score.

Quick Summary

Tuna is classified as an acid-forming food based on its Potential Renal Acid Load (PRAL) score. This is due to the sulfur-containing amino acids found in its high protein content. However, its mild acidity and anti-inflammatory omega-3s can be beneficial for many people, including those with acid reflux, depending on how it's prepared.

Key Points

Tuna is acid-forming: Based on its Potential Renal Acid Load (PRAL) score, tuna has a positive value, classifying it as an acid-forming food after digestion.
Acidity differs from reflux trigger: While acid-forming, lean tuna is often acceptable for individuals with acid reflux (GERD), as it is not a primary trigger for many people.
Preparation affects impact: Adding high-fat ingredients like excess mayonnaise can increase the likelihood of acid reflux symptoms, whereas lean, water-packed tuna is generally better tolerated.
High in protein and omega-3s: Tuna is a nutrient-dense food, providing high-quality protein, heart-healthy omega-3 fatty acids, and essential vitamins and minerals.
Mercury levels vary by type: Smaller tuna species, like skipjack (often used in 'light' canned tuna), contain less mercury than larger species like albacore.
Balancing with alkaline foods: Pairing tuna with alkaline-forming foods like vegetables can help create a more balanced meal.

The Science Behind Acid-Forming Foods

When we discuss whether a food is 'acidic' or 'alkaline', it's important to distinguish between two different concepts: the food's intrinsic pH level and its Potential Renal Acid Load (PRAL). The pH measures the acidity of a substance directly, with values below 7 being acidic and above 7 being alkaline. A food's PRAL score, however, measures the amount of acid or alkali it produces after being metabolized by the body. This is a more relevant metric for those concerned with the effect of food on their body's acid-alkaline balance.

Tuna's PRAL Score: A Quantitative Look

Unlike citrus fruits, which are acidic in nature but become alkaline-forming after digestion, tuna has a positive PRAL score, meaning it is considered acid-forming. This is a result of the high concentration of sulfur-containing amino acids in its protein. When these amino acids are broken down, they produce sulfuric acid, which contributes to the body's overall acid load. For example, canned light tuna drained of water has a PRAL score of approximately 12.7, indicating a moderate acid-forming effect.

Canned Tuna vs. Fresh Tuna: Does Processing Change Acidity?

Both fresh and canned tuna are considered acid-forming, though the preparation and packaging can influence other nutritional factors. Fresh tuna typically has a pH below 6.0, which is naturally acidic, and a positive PRAL score. Canned tuna, whether packed in oil or water, retains this acid-forming quality. However, the choice of packing liquid can impact the overall fat, calorie, and sodium content, which can be important for individuals with specific health concerns like acid reflux.

The Impact of Added Ingredients

It is also essential to consider what you mix with your tuna, as this can significantly alter the dish's overall acid-alkaline balance. For instance, a tuna salad made with a lot of mayonnaise can add more fat and calories, while other ingredients can help neutralize the acidity. Incorporating alkaline-forming foods is a strategic way to balance out the meal. Here are some examples of alkaline-forming foods to pair with tuna:

Vegetables: Spinach, kale, cucumber, broccoli, and carrots.
Herbs and Spices: Basil, thyme, parsley.
Healthy Fats: Avocado and olive oil (in moderation).
Legumes: Lentils and chickpeas.

Is Tuna Good for Acid Reflux? A Closer Look

Despite being categorized as an acid-forming food, tuna is often considered acceptable for those with gastroesophageal reflux disease (GERD). Many sources, including gastroenterologists, note that lean proteins like tuna are typically well-tolerated. This is because the overall food composition is more important than its PRAL score in triggering reflux symptoms. In fact, the omega-3 fatty acids in tuna can have anti-inflammatory effects that may benefit some individuals with GERD. Opting for canned tuna packed in water and minimizing high-fat additions like excessive mayonnaise can further reduce the risk of triggering symptoms.

Nutritional Benefits of Tuna

Beyond the acid-alkaline debate, tuna offers a wealth of nutritional benefits that make it a valuable part of a balanced diet. This is particularly true for canned tuna, which provides an affordable and convenient source of high-quality nutrition.

Excellent source of protein: Tuna is packed with complete protein, providing all the essential amino acids needed for muscle repair and building.
Rich in Omega-3 fatty acids: Especially beneficial for heart, brain, and eye health. Canned albacore is particularly high in omega-3s.
Source of Vitamin B12: Essential for metabolism, red blood cell production, and neurological function.
Provides key minerals: Including selenium, which acts as an antioxidant, and Vitamin D, crucial for bone health and immune function.

Comparison: Canned Tuna in Water vs. Oil


Feature	Canned Tuna (in Water)	Canned Tuna (in Oil)
Calories	Lower	Higher
Total Fat	Less than 1g/oz	Around 2g/oz
Saturated Fat	Lower	Higher
Sodium	Variable, but often lower than oil-packed	Can be higher, check labels
Omega-3s	Often higher in DHA	Good source, but fat content is higher
Texture	Flakier, drier	Moister, softer
Suitability for GERD	Generally preferable due to lower fat	May trigger symptoms in some due to higher fat

Mercury and Moderation

One important consideration when consuming tuna is its mercury content. Methylmercury can accumulate in fish, and larger, older tuna species like albacore generally have higher levels than smaller, younger ones like skipjack. For most adults, moderate consumption is safe, with the FDA and EPA recommending 2-3 servings per week of low-mercury fish. However, pregnant women, nursing mothers, and young children should be more cautious and limit consumption of high-mercury varieties. For up-to-date guidance, it is advisable to consult the FDA's recommendations on seafood safety.

Conclusion: Making an Informed Choice

In summary, while is tuna considered acidic in the context of its PRAL score, it is also a highly nutritious food that can be safely incorporated into most diets. Its acid-forming nature after digestion is well-managed by the body's natural buffering systems, and for those with acid reflux, preparation methods and lean varieties are key. By pairing tuna with alkaline-forming vegetables and opting for water-packed versions, you can enjoy its many health benefits while maintaining a balanced diet. Ultimately, a varied and balanced diet remains the best approach to overall nutritional health. For individuals with chronic health conditions, consulting a healthcare provider or registered dietitian is always the best course of action.

Frequently Asked Questions

Canned tuna, like fresh tuna, is considered an acid-forming food based on its Potential Renal Acid Load (PRAL) score, though its natural pH is mildly acidic. However, its specific impact on an individual's body can depend on how it's prepared and other foods it's eaten with.

Tuna does not necessarily cause acid reflux. As a lean protein, tuna is often well-tolerated by those with GERD. While it is an acid-forming food, its anti-inflammatory omega-3s can even be beneficial. Issues may arise from high-fat preparation, so opting for water-packed tuna is often recommended.

All varieties of tuna are considered acid-forming after digestion. However, in terms of mercury content and potential health risks, smaller species like skipjack (often labeled as 'light' tuna) have lower levels than larger varieties like albacore.

The pH level of fresh tuna typically falls below 6.0, indicating it is naturally acidic. For example, yellowfin tuna has an average pH of around 5.9.

To create a more balanced meal, you can pair tuna with alkaline-forming foods. Mix it with chopped vegetables like cucumbers or celery, serve it on a bed of spinach or lettuce, and use a minimal amount of low-fat mayonnaise or an olive oil-based dressing.

Tuna is a high-protein food, and like most other fish and meats, it is categorized as acid-forming due to its PRAL score. The specific PRAL score can vary by fish, but all animal proteins contribute to the body's acid load.

Yes. Tuna is an excellent source of high-quality protein, omega-3 fatty acids, vitamin B12, vitamin D, and selenium. These nutrients support heart health, brain function, and overall well-being, making tuna a valuable addition to a balanced diet when consumed in moderation.