Conjugated Linoleic Acid

In fact, one fat soluble nutrient called CLA is found chiefly in the fat of grass fed ruminant animals - in butterfat and the fat attached to beef and lamb. In studies involving both animals and humans, CLA has been shown to encourage the build up of muscle and the reduction of adipose fat. When animals are raised in confinement and given dry feed, the CLA component of their fat disappears.

— Thomas Cowan MD.
The Fourfold Path to Healing