Tuna is one of the best foods you can eat for both weight loss and muscle gain. A single can of light tuna packed in water (165g) delivers 42 grams of protein for just 191 calories and 1.4 grams of fat. That ratio of protein to calories is hard to beat with almost any other whole food, making tuna a staple for people trying to lose fat while building or preserving muscle.
Why Tuna Works for Weight Loss
Weight loss comes down to eating fewer calories than you burn, and tuna makes that easier in two ways. First, it’s extremely calorie-sparse. You can eat a full can of water-packed tuna and take in fewer than 200 calories while still feeling full. Compare that to other protein sources like ground beef or cheese, where the same amount of protein comes bundled with significantly more fat and calories.
Second, protein is the most satiating macronutrient. It keeps you fuller for longer than carbohydrates or fat, which means you’re less likely to snack or overeat at your next meal. Protein also has the highest thermic effect of any macronutrient, meaning your body burns more energy digesting and processing protein than it does with carbs or fat. Roughly 20 to 30 percent of the calories from protein get used up during digestion alone. When a large portion of your diet comes from lean protein like tuna, these effects add up over time.
Why Tuna Works for Muscle Gain
Building muscle requires adequate protein intake, typically in the range of 1.6 to 2.2 grams per kilogram of body weight per day for people who train regularly. Tuna makes hitting that target straightforward. One can provides over 40 grams of complete protein, meaning it contains all nine essential amino acids your muscles need to repair and grow after resistance training. For a 170-pound person aiming for around 140 grams of protein daily, a single can covers nearly a third of that goal.
Tuna also contains omega-3 fatty acids, which play a role in recovery. A study at Georgia State University found that omega-3 supplementation significantly reduced perceived muscle soreness and lowered inflammatory markers after exercise-induced muscle damage. Omega-3s won’t build muscle on their own, but by helping you recover faster and train more consistently, they support the overall process. Albacore tuna tends to be higher in omega-3s than light tuna, though both contribute meaningful amounts.
Water-Packed vs. Oil-Packed Tuna
The type of liquid in the can matters more than most people realize. A 5-ounce can of tuna in water has about 120 calories, while the same size can packed in oil jumps to around 280 calories. That’s more than double the energy for essentially the same amount of protein. If you’re trying to lose weight, water-packed tuna is the clear winner.
Interestingly, water-packed tuna also retains more omega-3s. Per ounce, water-packed tuna contains about 56 mg of DHA compared to just 29 mg in oil-packed tuna. The vegetable oil used in packing can leach some of the natural omega-3s out of the fish. So water-packed tuna gives you fewer calories, more omega-3s, and the same protein. Oil-packed tuna isn’t a bad food, but if your goals are fat loss and muscle gain, water-packed is the better choice.
How Much Tuna You Can Safely Eat
Mercury is the main reason you can’t eat tuna at every meal. All tuna contains some mercury, but the amount varies significantly by species. Skipjack tuna, sold as “light tuna,” has the lowest mercury levels of all commercial tuna, averaging well below the U.S. consumption guideline of 0.22 parts per million. The FDA classifies it as a “Best Choice” fish, safe for two to three servings per week.
Albacore (labeled “white tuna”) and yellowfin (often sold as “ahi”) both have average mercury concentrations above that 0.22 ppm threshold. The FDA lists these as “Good Choices,” recommending no more than one serving per week. The Biodiversity Research Institute’s analysis suggests an even more conservative approach for albacore and yellowfin: roughly one meal per month for people who want to stay well below concerning levels.
For practical purposes, if you’re relying on tuna as a regular protein source, stick mostly with canned light tuna and limit albacore or yellowfin to occasional meals. This lets you eat tuna several times a week without worrying about mercury accumulation.
How to Fit Tuna Into Your Routine
Tuna’s biggest advantage beyond its nutrition is convenience. A can requires no cooking, no refrigeration until opened, and costs a fraction of what fresh fish or chicken breast does per gram of protein. You can keep several cans in your desk, gym bag, or pantry and have a high-protein meal or snack ready in under a minute.
That said, eating plain tuna from a can gets old fast. Mixing it with Greek yogurt instead of mayonnaise keeps the protein high and calories low. Adding it to salads, whole grain wraps, or rice bowls gives you a complete meal with fiber and complex carbohydrates. Pairing tuna with a carb source after training can help replenish glycogen stores while the protein supports muscle repair.
If you’re in a serious calorie deficit, tuna is especially useful because it lets you eat a satisfying volume of food without using up much of your daily calorie budget. And if you’re in a slight surplus to build muscle, tuna helps you load up on protein without accidentally overshooting your fat intake the way fattier protein sources can. It works well in both directions, which is why it shows up so consistently in the diets of bodybuilders, athletes, and anyone tracking macros closely.
Limitations to Keep in Mind
Tuna alone won’t transform your body. No single food will. You still need a well-structured training program, adequate total calories, and a balanced diet with fruits, vegetables, healthy fats, and fiber. Tuna is also very low in fat, which is great for keeping calories down but means you need to get essential fatty acids and fat-soluble vitamins from other sources in your diet.
There’s also the palatability issue. Some people burn out on tuna quickly, especially when eating it multiple times a week. Rotating it with other lean proteins like chicken breast, egg whites, cottage cheese, or other fish keeps your diet sustainable, which is ultimately what matters most for long-term results. The best protein source is the one you’ll actually eat consistently for months, not just weeks.