Most beef sold in stores has white fat. This is grain-fed beef. Grass-fed beef has yellow fat due to the chlorophyll in the grass. The difference is the Food Pyramid. A grass-fed steer weighs about 800 pounds depending on breed. Take this steer and feed it grain for 6 months and the weight will nearly double to 1500 pounds and the fat will turn white. It could well be that humans are not evolutionarily adapted to eat grain-fed beef, so there is a possible connection between feed-lot sourced red meat and heart disease.