Tuna is lower in calories and higher in protein per serving, making it the slightly better option if your only goal is cutting calories. Per 100 grams, bluefin tuna delivers 144 calories and 23 grams of protein, while Atlantic salmon comes in at 197 calories, 20 grams of protein, and nearly three times the fat. But the full picture is more nuanced, because salmon’s extra fat comes with metabolic benefits that can support weight loss in ways that go beyond simple calorie math.
Calories and Protein Side by Side
The calorie gap between these two fish is meaningful if you eat them regularly. Over a 100-gram serving (roughly a palm-sized fillet), tuna saves you about 53 calories and gives you 3 extra grams of protein. That protein difference adds up: higher-protein meals keep you fuller longer and require more energy to digest, which means your body burns more calories just processing the food.
Tuna’s advantage grows even larger when you look at canned options. A 5-ounce can of tuna packed in water has just 120 calories, while the same can packed in oil jumps to 280 calories. If you’re buying canned tuna for weight loss, always choose water-packed. The protein content stays nearly identical between the two, but you cut your fat intake by more than half.
Why Salmon’s Fat Isn’t a Disadvantage
Salmon contains about 13 grams of fat per 100-gram serving compared to tuna’s 5 grams. Most of that extra fat comes from omega-3 fatty acids, and these fats actively work against weight gain through several pathways. They shift your body’s fuel processing away from storing fat and toward burning it by activating genes involved in fat oxidation in both the liver and muscle tissue. They also increase your cells’ capacity to burn fat by boosting the number and efficiency of mitochondria, the energy-producing structures inside your cells.
Omega-3s also improve your body’s response to leptin, a hormone that signals fullness. When leptin sensitivity is impaired (common in people carrying extra weight), your brain doesn’t get the message that you’ve eaten enough. By reducing inflammation, omega-3s help restore that signaling. On top of that, these fats suppress the creation of new fat in the liver and reduce the production of fat-carrying particles in the bloodstream.
So while salmon has more calories on paper, its fat content is actively working to improve how your body handles energy storage. For someone eating at a moderate calorie deficit, this metabolic support can matter more than a 53-calorie difference.
Vitamin D and Weight Loss
Wild-caught salmon is one of the richest natural sources of vitamin D, providing roughly 988 IU per 3.5-ounce serving. Farmed salmon drops to about 240 IU, and tuna (yellowfin/ahi) falls in the middle at around 404 IU. Low vitamin D levels are consistently linked to higher body fat and greater difficulty losing weight. If you’re already deficient, which a large portion of adults are, choosing wild salmon gives you a substantial dose of a nutrient that supports healthy metabolism without needing a supplement.
Mercury: How Often You Can Eat Each
Salmon is in the EPA and FDA’s “Best Choices” category, meaning you can safely eat two to three servings per week. Most canned light tuna (skipjack) also falls into this lower-mercury tier, making it a safe regular choice. Albacore (white) tuna contains more mercury and lands in the “Good Choices” category, which limits you to one serving per week.
This matters for weight loss because consistency is what drives results. A fish you can eat three times a week is more useful than one you need to limit. Both salmon and canned light tuna give you that flexibility, but if you prefer albacore for its meatier texture, plan your meals accordingly.
Cost per Serving
Budget plays a real role in whether a food becomes a diet staple or a once-a-week treat. Canned light tuna is the clear winner here, costing roughly $1.10 per 25 grams of protein. Frozen salmon fillets come in around $1.80 per 25 grams of protein, making them a reasonable middle ground. Fresh Atlantic salmon runs about $2.40, and fresh yellowfin tuna steaks are the most expensive option at roughly $2.80 per 25 grams of protein.
If you’re on a tight budget, rotating between canned light tuna (in water) during the week and a fresh or frozen salmon fillet once or twice a week gives you the best combination of low cost, high protein, and omega-3 benefits.
Which to Choose for Your Goals
If you’re counting every calorie strictly and want the leanest possible protein source, canned tuna in water is hard to beat. At 120 calories per can with roughly 30 grams of protein, it’s one of the most efficient protein sources available at any price point. It works especially well as a quick lunch option: no cooking required, shelf-stable, and easy to portion.
If you’re taking a broader approach to weight loss and care about satiety, hormonal balance, and long-term metabolic health, salmon earns its extra calories. The omega-3 content, the vitamin D boost, and the richer flavor that makes meals more satisfying all contribute to a diet you can actually stick with. People who feel deprived on a diet don’t stay on it, and salmon’s richness can help prevent that.
The most practical answer for most people is to eat both. Use canned tuna for easy, low-calorie meals when you need to keep things simple, and cook salmon when you want something more filling that delivers broader nutritional benefits. Two to three total servings of fish per week, split between the two, covers your protein needs, keeps mercury exposure low, and gives you a steady supply of omega-3s without blowing your calorie budget.