Tuna is the second-most popular seafood eaten in America, according to a survey published by the National Marine Fisheries Services in 2009. Canning tuna is the easiest way to preserve it. The tuna is cooked, then packed in water or oil. The canning process ensures the tuna lasts for up to four years before it starts to go bad.
Water vs. Oil
Consumers have a choice between tuna packed in brine, oil or water when purchasing canned tuna. The latter two are by far the most popular. Tuna packed in oil has almost twice the calories as tuna packed in water. On average, tuna packed in spring water has 220 calories per serving, while tuna packed in oil has 331 calories. It's the mayonnaise that many use to make tuna salad that has the greater health impact, however. Tuna packed in water and mixed with 2 tbsp. of mayonnaise has more fat than tuna packed in oil and mixed with only 1 tbsp. of mayonnaise.
Water and oil should be drained from canned tuna before use, according to the U.S. Food and Drug administration,. A sieve should be used to drain as much water and oil from canned tuna as possible. Then, the tuna should be left to sit in the sieve for at least 2 minutes. While these instructions are meant for people who are preparing tuna samples for laboratory analysis, they will work equally well for home consumers. Or, simply drain the tuna by straining the liquid through the lid, or with a strainer.
Reasons to Drain Water
Draining the tuna does not lower the levels of mercury, because mercury is not water-soluble. It also does not reduce the amount of calories and fat you will consume, because unlike oil, water does not contain extra fat and calories. Still, draining the water makes the tuna easier to use in recipes. Canned tuna is used to make tuna salad, which is usually some combination of mayonnaise, onions, cucumbers and seasoning. This paste is then spread on sandwiches and crackers. Canned tuna can also be sprinkled on pasta or salad greens. If left undrained, the tuna would be too watery to use in tuna salad or pasta. If you want to eat the tuna straight from the can, you do not have to drain the water from it.
Reasons to Drain Oil
Consumers drain the oil from canned tuna for the reasons mentioned above, but also because oil contains a lot of extra fat and calories. In addition, the slippery texture of the oil may be off-putting to some. For that reason, many consumers who purchase tuna canned in oil may also rinse off the fish to get rid of residual oil before using it in recipes or tuna salad. Note, however, healthy Omega-3 acids leach from tuna into the surrounding oil. So, when you drain the oil, you are also draining some of those beneficial fatty acids.