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Fresh and frozen tuna are excellent sources of long chain omega-3 polyunsaturates, supplying around 5% total oil of which 20% is omega-3. However, during the canning process, most of the oil and therefore most of the omega-3 is lost. This is mainly because tuna is cooked before it is canned, and during the cooking process much of the oil is separated and lost. The meat that goes in the tin thus has a low oil content (usually less than 1g per 100g) and a low omega-3 content (usually less than 0.4g per 100g). It matters little whether the tuna is albacore or yellowfin because once it is canned there is little omega-3 left. Some tuna packers do can raw tuna so that the omega-3 content is higher, but it is usually difficult to distinguish such products from the others in the marketplace. Enquire of the producer to be certain. These comments only apply to tuna. Other canned fish are just as good as the raw fish as sources of long chain omega-3 polyunsaturates.
