Defatting a beef liver means removing its fat, and with that fat many of the fat-soluble vitamins. That’s why it’s important to choose beef liver supplements that contain non-defatted liver. All of the products I recommend above fall into that category. Considering that some supplements manufacturers make it a point to mention that the livers they used are non-defatted, it’s reasonable to assume that others use defatted livers. Why someone would want to remove fat from the liver before freeze-drying it is beyond me.