If you want to lose weight, and you don’t hate fish, you can lose weight twice as fast eating fish, compared to eating meat. Low fat white fish (cod, halibut, turbot, flounder, roughy) generally has 20-30 calories an ounce. Higher fat red fish (salmon, swordfish, tuna) has 40-50 calories an ounce. Take it easy on swordfish, tuna, mackerel and tilefish however – probably best to eat these no more than once a week, and not at all if you’re pregnant – because of the mercury content. The leanest steak (sirloin or filet mignon) has 50 calories an ounce. A fatty ribeye or delmonico steak can have 80-100 calories an ounce. So you can lose weight twice as fast eating lower fat fish, compared to eating higher fat meat.