The World's Healthiest Foods

Does canned fish (salmon or tuna) have any sort of nutritional benefit when compared to fresh fish?

Assuming that you cook your fresh salmon and tuna in a healthy way (we have several suggested cooking methods on our website), fresh salmon and tuna are going to have many nutritional advantages over canned salmon and tuna. But the details here are a little more complicated, and worthy of a bit more explanation.

There are usually two heating stages in the canning of fish. These stages are called "pre-treatment" and "retorting." During pre-treatment, before the fish is placed in the can, it is typically heated, often using steam (about 212F) for 1-8 hours, depending on the size of the fish. After the fillers, oils, brines, salts, or other components are added along with the fish to the can, there's a second round of heating, called retorting. Depending on the can size and other factors, about 1-3 hours are required at a temperature of about 240F. The numbers above are typical for tuna, and would vary for the canning of other fish.

Degree of heat and heat duration are key factors affecting nutrient loss not only in the canning of fish, but with the cooking of all foods. If a fish has colorful pigments like carotenoids (part of the pre-vitamin A in salmon), the total amount will decrease with cooking. The amount of vitamin A retained in cooked salmon might appear to look higher than the amount found in raw salmon in some nutrition databases, but once you get the gram weight and edible portion sizes identical, you'll find the raw salmon to contain more. When you bring in the canning factor, you usually get another 15-35% drop here.

This two-fold heating process can take a significant toll on some of the nutrients found in fish. To help lessen the impact, some companies skip the pre-treatment process and place the fish into the can in fresh, raw form. When the cooking of the fish occurs only in the sealed can, the nutrient loss is less. Most of the companies that cook only in the can emphasize wild caught fish and are focused on both environmental and health issues. You may need to search for this type of canned fish on the internet, because many stores do not routinely stock it.

There is one important exception to the nutrient loss from the heating process above, and that exception is calcium. Canned salmon has a considerably higher concentration of calcium than fresh salmon (about 10-20 times higher). This is because salmon is canned with its calcium-rich bones; the canning process softens them so they are easily ingested with the meat of the fish.

Although we do not have specific data on canned versus fresh sardines, we would expect that this would also be the case for them or any other type of canned fish in which you see bones. Since the bones of sardines are quite small and many people eat them even when cooking fresh sardines, the canned version might not turn out to have that much calcium advantage. Because tuna is not canned with bones, fresh tuna has more calcium than canned -about twice as much—however tuna is not a good source of calcium with a 6-ounce serving of freshly broiled tuna providing only about 35 milligrams of calcium.

In general, we believe that canned fish can serve as a satisfactory and convenient option to fresh fish, which is not always readily available.

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