Like a fish in water -- not oil. Fish such as salmon and tuna are rich in omega-3 fatty acids which reduce total blood fats, lower bad cholesterol and raise good cholesterol. Although fresh tuna is the best way to go, canned tuna is often most affordable and convenient. Be careful when making your selection. While fish packed in oil may be the moistest, it is higher in fat. The oil is also rich in omega-6 fatty acids, which people tend to get too much of. Go for tuna packed in water or broth. If you're dieting, then tuna can be one of the best and most inexpensive protein sources. It's also quick to prepare, but think outside the mayo and relish. Drain the tuna and add a little soy and fresh grated ginger to the tuna. If you'd like to make it heartier, then add it to cooked brown rice for a one-dish meal.