While we might not call canned tuna "bad," we would definitely not recommend eating regular canned tuna in water every day for lunch. We are actually not big fans of eating the same thing, regardless of what it is, every day for the same meal. Foods need to be varied, and combined throughout the week in a way that gives each person the best chance of receiving all nutrients. No one food contains everything that a person needs to be well-nourished.
We have a special concern about tuna, and that concern is unwanted mercury contamination. Because of its mercury content we think it may be best for people to limit their intake. This is especially important for children, women who are pregnant, lactating or of childbearing age and those with weakened immune systems. In the spring of 2004, the U.S. Food and Drug Administration (FDA) issued a recommendation that pregnant and nursing women, women of childbearing age and children limit their consumption of canned albacore tuna and tuna steaks to no more than 6 ounces per week and light tuna to no more than 12 ounces per week. (Light tuna has been found to contain less mercury than albacore tuna. While albacore is actually a biological species of tuna, "light" tuna may consist of several different species, including skipjack, bluefin, yellowfin, and tongol. All types except tongol may be labeled "chunk light" or "solid light", while tongol may only be labeled "chunk light".) Our recommendation when purchasing tuna is to stick with canned light versions, or if buying canned albacore, to purchase it from a reputable supplier who has had the mercury levels tested by an independent lab.
The mercury content of other types of fish will vary with the species. If you are looking for some other options that could replace your canned tuna, some varieties recommended by the Environmental Working Group and the U.S. Public Interest Group include wild Pacific salmon, flounder, haddock, shrimp, farm-raised trout and catfish; there was no mercury detected in these fish.
For more information on this topic, see: