Tuna is one of the best foods you can eat for weight loss. A single ounce of canned tuna in water has just 24 calories and 6 grams of protein, making it one of the most protein-dense, low-calorie foods available. Whether you’re counting calories, tracking macros, or simply trying to eat leaner, tuna checks nearly every box.
Why Tuna Works So Well for Weight Loss
The reason tuna keeps showing up in diet plans comes down to its protein-to-calorie ratio. Per 100 grams, canned tuna in water delivers roughly 24 grams of protein for under 100 calories. That’s hard to beat, even compared to chicken breast. Protein is the most satiating macronutrient, meaning it keeps you full longer than the same number of calories from carbs or fat.
Protein also costs your body more energy to digest. Your metabolic rate increases by 15 to 30 percent when processing protein, compared to much smaller bumps from carbs and fat. This is called the thermic effect of food, and it means a meaningful chunk of the calories in your tuna never actually “count” because they’re burned during digestion itself. Over weeks and months of a high-protein diet, that adds up.
Water Pack vs. Oil Pack
The packing liquid makes a bigger difference than most people realize. One ounce of tuna in oil contains 56 calories and 2.3 grams of fat. The same amount packed in water drops to 24 calories and 0.9 grams of fat. That’s less than half the calories for a similar amount of protein. Over a whole can, the difference can easily be 100 calories or more.
If you’re on a calorie deficit, water-packed tuna is the clear winner. Oil-packed versions aren’t unhealthy, but the added fat doesn’t offer much nutritional advantage since most brands use soybean or sunflower oil rather than anything rich in omega-3s. Spring water is the best option overall: it preserves the omega-3 content without adding sodium or unnecessary fat. Brine-packed tuna is a close second and often cheaper. A good rinse under the tap removes much of the added salt.
Omega-3s and Other Nutritional Benefits
Beyond its diet-friendly calorie count, tuna provides omega-3 fatty acids that support heart health, reduce inflammation, and may help with fat metabolism. But the amount varies dramatically by species. A four-ounce serving of albacore (white) tuna delivers around 1,000 milligrams of omega-3s when canned, and up to 1,700 milligrams when fresh. Light canned tuna, typically skipjack, provides only 150 to 300 milligrams per serving.
If omega-3 intake matters to you, albacore is the better choice. If your priority is strictly calories and protein, light tuna works just as well and is usually cheaper. Both fresh and canned tuna provide comparable omega-3 levels, so you’re not losing nutritional value by choosing the can.
Tuna also supplies selenium, B vitamins, and vitamin D. Selenium plays a protective role in the body, helping neutralize oxidative damage, and tuna happens to be one of the richest dietary sources.
How Much Tuna Is Safe to Eat Weekly
Mercury is the main reason you can’t just eat tuna at every meal. The EPA and FDA recommend adults eat two to three servings per week from the “Best Choices” category of fish (which includes light/skipjack tuna) or one serving per week from the “Good Choices” category (which includes albacore). A serving is four ounces cooked, roughly the size of a deck of cards.
For pregnant or breastfeeding women, the guidance is 8 to 12 ounces per week total of lower-mercury seafood. Children should stick to two servings per week from the lowest-mercury options. Light canned tuna contains less mercury than albacore, so it allows for more frequent consumption.
One reassuring detail: tuna naturally contains selenium in amounts that exceed its mercury content. Research on tuna sold commercially found positive “selenium health benefit values” in all samples tested, both fresh and canned. Selenium binds to mercury in the body, which helps reduce its harmful effects. This doesn’t mean mercury is harmless, but it does mean that moderate tuna consumption carries less risk than the raw mercury numbers might suggest.
Practical Ways to Use Tuna on a Diet
A can of tuna in water is one of the most convenient protein sources you can keep in your kitchen. It requires zero cooking, stores for years, and costs a fraction of fresh fish or chicken. For a quick, high-protein meal under 300 calories, mix a can with Greek yogurt instead of mayo, add mustard and diced celery, and eat it on whole grain toast or over a bed of greens.
Tuna also pairs well with eggs for a protein-heavy breakfast scramble, works in rice bowls with vegetables and soy sauce, or can be formed into patties and pan-seared with minimal oil. The neutral flavor absorbs seasonings easily, which helps if you’re eating it multiple times a week and want variety.
If you’re following a structured diet plan, one can of tuna in water (roughly five ounces drained) gives you about 30 grams of protein for approximately 120 calories. That’s comparable to a scoop of whey protein but with real food, more micronutrients, and greater satiety.
Sodium and Processed Tuna
Standard canned tuna can contain a surprising amount of sodium, especially brine-packed varieties. If you’re watching your salt intake, look for cans labeled “low sodium” or “no salt added.” Rinsing brine-packed tuna under running water for 30 seconds removes a significant portion of the surface sodium while keeping the protein and omega-3s intact.
One issue worth knowing about: a 2023 study examining canned fish found microplastic particles in every sample tested, with an average of about 4 particles per 100 grams. The levels varied widely by brand and packing method. This is a concern across all canned and packaged foods, not unique to tuna, but it’s worth being aware of if you’re eating canned tuna daily. Rotating between canned and fresh tuna, or between tuna and other lean proteins, is a reasonable approach.
Where Tuna Fits in Your Overall Diet
Tuna works best as a regular rotation player rather than your sole protein source. Eating it two to three times per week keeps you well within mercury safety guidelines while giving you a reliable, low-calorie protein hit. On other days, lean chicken, eggs, legumes, or other fish fill the same role.
For pure weight loss efficiency, few whole foods match canned tuna in water. It’s cheap, shelf-stable, requires no prep, and delivers one of the highest protein-per-calorie ratios of any food you can buy. The only real limitation is mercury, and staying within the recommended two to three servings per week handles that easily.