A couple of decades ago scientists believed that the polyunsaturated kind was more desirable. Now researchers are voting for the mono-unsaturated variety. Like polyunsaturated fat, it decreases the amount of LDL in the bloodstream. Unlike polyunsaturated fat, it doesn't decrease the amount of high-density lipoprotein (HDL) in the bloodstream. HDLs are highly beneficial because they tend to remove excess cholesterol from the circulatory system. This helps explain why olive oil has become the desired fat for consumption among informed cholesterol watchers - approximately three-fourths of its oil is mono-unsaturated.