Your best choice here is canned tuna. While the process of canning causes the fish to lose some of its heart-healthy fat, canned tuna comes form smaller, younger fish and therefore has less mercury than fresh tuna. White tuna has more omega-3 fats than light tuna, but also slightly higher mercury levels. Buy canned tuna packed in water rather than oil because it retains more or its omega-3 fats after draining.

Fresh tuna steaks aren’t a great choice. They come from larger, older fish, which harbour the highest mercury levels. And the tuna steaks sold in this country are usually yellowfin, a species with low levels of omega-3 fat. If you’re pregnant or trying to conceive, you should limit your consumption of canned tuna to one serving a month and avoid fresh tuna. Doing so will limit your exposure to mercury, which can damage developing brains.