A 6-inch Subway tuna sub on wheat bread has 479 calories, 25 grams of fat, and 20 grams of protein. That puts it in the middle of the pack for fast-food sandwiches, but the high fat content, mostly from mayonnaise, makes it less healthy than it first appears. Whether it works for your diet depends on how you customize it and how often you eat it.
What’s Actually in It
Subway’s tuna filling has three main components: flaked tuna in brine (the company says it uses skipjack and yellowfin species), mayonnaise, and an additive to protect flavor. That additive is calcium disodium EDTA, a common preservative. The mayonnaise is made from soybean oil, eggs, water, distilled vinegar, salt, sugar, spice, and lemon juice concentrate, with no artificial flavors and zero grams of added sugar.
The simplicity of the filling is actually a point in its favor compared to more processed sandwich meats. But the generous amount of mayo mixed into the tuna is what drives the fat and calorie count up significantly.
The Nutrition Breakdown
For a standard 6-inch tuna sub on wheat bread:
- Calories: 479
- Total fat: 25 grams
- Saturated fat: 4 grams
- Protein: 20 grams
- Sodium: 620 milligrams (about 27% of the recommended daily limit of 2,300 mg)
A footlong tuna sub clocks in at roughly 1,360 calories, putting it near the top of Subway’s menu alongside options like the Chicken and Bacon Ranch at 1,410 calories. For comparison, a footlong Veggie Delite is 400 calories and a Black Forest Ham is 670. If you’re ordering a footlong tuna, you’re eating a calorie-dense meal that rivals some of Subway’s least nutritious options.
The 25 grams of fat in a 6-inch sub is the real issue. Most of that comes from the soybean oil in the mayonnaise rather than from the tuna itself. Plain tuna is a lean protein, but once it’s mixed with mayo, it behaves more like a high-fat food. The saturated fat at 4 grams is relatively modest, though, meaning most of the fat is unsaturated.
The Tuna Authenticity Question
You may have heard about the lawsuit claiming Subway’s tuna isn’t actually tuna. In 2021, lab tests commissioned by both the plaintiffs’ attorney and the New York Times failed to find identifiable tuna DNA in samples from Subway sandwiches. A lab spokesperson suggested two possible explanations: either the tuna was so heavily processed that its DNA couldn’t be identified, or it wasn’t tuna at all.
Subway has consistently maintained that it delivers 100% cooked tuna to its restaurants. The plaintiffs eventually shifted their legal argument, no longer claiming the tuna wasn’t tuna but instead questioning whether it was “100% sustainably caught skipjack and yellowfin tuna” as advertised. DNA testing of heavily cooked and processed fish is notoriously unreliable, so the results don’t prove fraud. But they don’t fully settle the question either.
Mercury Levels in Subway’s Tuna
Tuna naturally contains mercury, and the amount varies by species. Skipjack, which Subway says it primarily uses, is one of the lower-mercury options. FDA monitoring data shows skipjack averages 0.144 parts per million of mercury, roughly comparable to canned light tuna at 0.126 ppm. Yellowfin, the other species Subway reports using, averages higher at 0.354 ppm, similar to albacore.
For context, bigeye tuna sits at 0.689 ppm, nearly five times the skipjack level. If Subway’s tuna is predominantly skipjack, mercury exposure from eating it once or twice a week is low for most adults. Pregnant women and young children, who are more sensitive to mercury, should stick to two to three servings of lower-mercury fish per week as a general guideline.
How It Compares to Other Subway Options
The tuna sub lands in an awkward middle ground. It has decent protein at 20 grams per 6-inch serving and is naturally gluten-free (without the bread) and low-carb at just 7 grams of net carbs if ordered as a salad. Those qualities make it appealing for people watching their carb intake. But the calorie and fat counts are higher than turkey, ham, or chicken breast options that deliver similar or more protein with less fat.
Verywell Fit, a nutrition-focused publication, ranks the Veggie Delite among Subway’s most nutritious sandwiches. The tuna sub doesn’t make that list, largely because of its mayo-heavy preparation. If you want tuna’s benefits (omega-3 fatty acids, lean protein) without the caloric cost, ordering it as a chopped salad with oil and vinegar instead of the pre-mixed mayo version would cut the fat substantially, though Subway premixes its tuna with mayo before it reaches the store.
Making It Healthier
Since the tuna arrives already blended with mayonnaise, you can’t ask for less mayo in the tuna itself. But you can control everything else. Choosing a 6-inch over a footlong immediately cuts calories in half. Loading up on vegetables adds fiber and nutrients without meaningful calories. Skipping cheese removes another 40 to 50 calories and additional sodium. And choosing wheat bread over Italian herbs and cheese keeps the bread’s contribution modest.
The biggest lever you don’t have access to is the mayo ratio. This is what separates Subway’s tuna from, say, making tuna salad at home where you control how much mayo goes in. A homemade tuna sandwich with a tablespoon of mayo instead of the several tablespoons Subway uses could easily come in under 300 calories with the same protein.
A 6-inch Subway tuna sub is a reasonable occasional meal, not a health food. It delivers solid protein and omega-3s from the fish, but the heavy mayo preparation pushes it into higher-calorie territory than most people expect from a tuna sandwich. If you’re eating it once a week, the mercury and calorie concerns are minor. If it’s a daily choice, there are leaner options on the same menu.