#3: Tuna processors are processing out all the good stuff.

It's not just fishing methods that are unhealthy. The healthfulness of canned seafood, particularly tuna, takes a hit when the seafood industry gets its hands on it, says William Carvalho, owner of the sustainable seafood company Wild Planet.

Here's the standard method that a whole tuna gets from the ocean to a can, according to Carvalho: First, a frozen tuna gets defrosted and cooked under high heat and pressure in a huge oven. During that process, all the fats and oils drip out from the tuna and get collected to be resold as additives for animal feed or for other uses, for instance, fish oil supplements. Once it's cooked, workers strip the meat off the bone and send it into packaging machinery where it's placed into cans. "At that point, the meat is fairly dried out because it's already been roasted and is devoid of any juices and fat," Carvalho says. "If processors simply canned that, it would scorch and stick to the can." So processors add a solution of soy-based vegetable broth and pyrophosphate, a food additive. But those do more than just protect the meat from scorching, says Carvalho. The broth contains hydrolyzed vegetable protein, which binds to the pyrophosphate to create something that looks like tuna and therefore adds bulk and protein to the tuna meat that's already there, so it looks like you're getting a full 5 ounces of tuna, when in reality you're getting just 3.5 ounces of tuna and 1.5 ounces of water and additives. Finally, a lid is put on the can and the tuna is cooked a second time, for roughly an hour, to sterilize it.

All this "makes the cost of a tuna can cheaper," he says, but a breakdown of the three biggest supermarket brands shows just how much that cheap tuna is providing. (The figures below are based on 2-ounce servings of solid white albacore tuna in water.)

Bumble Bee: 13 g protein; 100 mg omega-3s

Chicken of the Sea: 13 g protein; 150 mg omega-3s

Starkist: 12 g protein; 110 mg omega-3s

Your Move: Eat healthier tuna.

Compare those figures with the three leading sustainable brands of tuna, which are packed more in line with Carvalho's method -- canning a full 5 ounces of raw tuna meat with a little salt and nothing more, then cooking it just once via pressure cooking to sterilize the can and the contents. "We capture the drippings that the conventional method loses during the first cooking phase in the can, and that becomes our liquid," he says. It also contains all the good omega-3s that make seafood so healthy (and more protein, which comes from fish, not from food additives).

American Tuna: 14 g protein; 2,667 to 3,333 mg omega-3s

Vital Choice: 16 g protein; 1,653 mg omega-3s

Wild Planet: 16 g protein; 1,340 mg omega-3s

As an added bonus, all of those brands catch younger tuna, which have lower levels of mercury than the larger fish favored by national brands, using much less environmentally damaging pole-and-line fishing methods.

The Best Canned Fish You've Never Tried

#4: The seafood you think you're eating is probably not what you're eating.

Increasing attention has been paid in recent years to the very serious issue of seafood fraud," in which distributors, retailers, or restaurateurs sell you mislabeled fish. For instance, labeling a fish as "tuna" when it is in fact eel. Sometimes the deception is intentional. Illegal fishermen, who catch between 13 and 31 percent of the world's seafood, often try to pass off their catch as something that came from a legitimate fishery, despite the fact that it may have been caught in violation of international quotas or treaties, Danson writes in Oceana. But often the mislabeling is unintentional, says Sharpless. "Sometimes the restaurateur is buying from a supplier who may or may not be reliable," he says, adding that, once a fish is filleted is becomes easy to pass off as anything an unscrupulous salesman says it is.

The result? You get environmentally damaging and potentially dangerous fish. Oceana has conducted studies in major cities across the U.S. and found that a third of all fish sold in grocery stores and restaurants -- sushi joints are particularly prone to fraud, they found -- is mislabeled. Their DNA testers found that fish labeled red snapper, an overfished species subject to tight regulation, was actually tilefish, which is known to harbor dangerously high mercury levels. Fish passed off as expensive tuna varieties in U.S. sushi restaurants were actually escolar, "a fish with such a nasty reputation for its gastrointestinal effects it's been dubbed the Ex-Lax fish," Sharpless writes in his book. Escolar is even banned in Japan.

Your move: Go big or go local.

"America could establish traceability and labeling requirements," Sharpless says, which would go a long way toward eliminating fraud. However, such labeling is unlikely anytime soon. Whole Foods, he says, has established a thorough seafood traceability program at its stores, as have a few other big-chain grocers. Alternatively, you can look for local fishermen who sell their local catch.

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