Tuna is an excellent source of selenium, vitamin B3 (niacin), vitamin B12, vitamin B6, iron and protein. It is a very good source of phosphorus as well as a good source of vitamin B1 (thiamin), vitamin B2 (riboflavin), choline, vitamin D, and the minerals potassium, iodine, and magnesium.
In 3 oz. of yellowfin tuna steak there are 110 calories, .5 g of fat and 24.78 g of protein.
3 oz. of bluefin tuna steak has 156 calories, 5.34 g of fat and 25 g of protein.
As well as helping to combat the symptoms of iron deficiency, tuna is a great source of Omega 3.