great source of protein while cutting, alot of protein, very low fat and carbs. There are different types with higher fat contents. As far as the mercury levels go, albacore is said to have the smallest amount. When eating anything from the ocean, it'll probably have traces of mercury. I used to eat 6 cans a day for 3 months while i was on a bulking cycle. I did get sick about 2.5 months into it. I dont know what it was contributed to though, but as long as you dont overdo it, mercury in tuna shouldnt be a concern.