Tuna is one of the most keto-friendly foods you can eat. A standard can of light tuna packed in water contains zero grams of carbohydrates and 42 grams of protein, making it an easy fit within any ketogenic diet. It also has a glycemic index of zero, meaning it causes no blood sugar response at all.
Tuna’s Macronutrient Breakdown
One drained can (165g) of light tuna in water delivers 42g of protein, 1.4g of fat, and 0g of carbs, fiber, or sugar. That zero-carb profile means tuna won’t touch your daily carb limit, whether you’re aiming for 20g or 50g of net carbs per day.
The one thing to note is that plain tuna is very lean. On a ketogenic diet, where 70–80% of your calories should come from fat, tuna alone won’t get you there. It’s a protein powerhouse, but you’ll want to pair it with fat sources to keep your macros balanced. More on that below.
Watch Out for Flavored Pouches
Plain tuna is carb-free, but flavored tuna products are a different story. StarKist’s Sweet & Spicy Tuna Creations pouch, for example, contains 4g of total carbs in a small 2.6 oz pouch, all of it from added sugars. The larger 6 oz pouch bumps that to 5g of carbs with 5g of added sugar. Other flavors like lemon pepper, ranch, and buffalo often contain similar hidden carbs from sugar, starches, or seasoning blends.
If you’re buying tuna specifically for keto, stick with plain chunk light or albacore packed in water or olive oil. Always check the ingredient list on flavored varieties for sugar, dextrose, or corn syrup solids.
Boosting the Fat Content
Since plain water-packed tuna is almost pure protein, you’ll want to add your own fat to make it a balanced keto meal. The simplest approach is tuna salad made with full-fat mayonnaise. Three tablespoons of real mayo (brands like Duke’s or Hellmann’s) adds roughly 30g of fat while keeping carbs near zero, which transforms a lean can of tuna into a proper high-fat meal.
Other ways to round out the fat:
- Avocado: Half an avocado adds about 15g of fat and only 2g of net carbs.
- Olive oil: Buying tuna packed in olive oil instead of water adds fat at the source. You can also drizzle extra virgin olive oil over a tuna plate.
- Cheese: Melting cheddar over a tuna dish or mixing in cream cheese works well for both flavor and fat.
- Hard-boiled eggs: A classic tuna salad addition that contributes both fat and protein.
Choosing tuna packed in olive oil rather than water is a simple swap if you’d rather not rely entirely on mayo. Just look for brands that use actual olive oil rather than a blend of soybean and olive oils.
Omega-3 Benefits
Beyond being keto-compatible, tuna is a strong source of omega-3 fatty acids, which support heart and brain health. A single serving of chunk light tuna in water provides roughly 650–710 mg of DHA and about 95 mg of EPA. Chunk white (albacore) in water offers around 760 mg of DHA and 170 mg of EPA per serving.
Interestingly, tuna packed in oil delivers significantly less omega-3 per serving. Albacore in oil drops to about 256 mg DHA and 36 mg EPA, likely because the omega-3s leach into the packing oil, which most people drain off. If omega-3 content is a priority for you, water-packed tuna is the better choice.
Mercury Limits to Keep in Mind
Tuna is affordable and convenient enough that many keto dieters eat it several times a week. That’s generally fine, but mercury exposure is worth tracking, especially with heavier consumption.
The EPA and FDA place canned light tuna (typically skipjack) in their “Best Choice” category, with an average mercury concentration of 0.13 parts per million. You can safely eat two to three servings per week. Albacore (white) tuna has nearly three times more mercury at 0.35 ppm, placing it in the “Good Choice” tier with a recommendation of no more than one serving per week.
A practical approach: make canned light tuna your everyday staple and treat albacore as an occasional upgrade. If you’re eating tuna daily on keto, rotating in other low-carb proteins like salmon, sardines, chicken thighs, or eggs a few days a week keeps mercury exposure well within safe limits while adding variety to your fat and nutrient profile.
Best Tuna Options for Keto
Not all canned tuna is equally suited to a ketogenic diet. Here’s a quick ranking:
- Chunk light in water: Zero carbs, low mercury, high omega-3s. The all-around best option. Add your own fat.
- Chunk light or albacore in olive oil: Zero carbs with built-in fat. Slightly lower omega-3 retention, but more convenient for on-the-go eating.
- Plain albacore in water: Zero carbs, excellent omega-3 content, but limit to once a week due to higher mercury.
- Flavored pouches: Convenient but often contain 4–5g of added sugar per pouch. Read labels carefully and avoid sweet or glazed varieties.
Tuna is one of the cheapest, most portable keto proteins available. A can in your desk drawer or a pouch in your bag is an easy way to stay on plan when other options aren’t available. Just keep it plain, add your own fat, and rotate your tuna types to manage mercury.