One of the most important characteristic in the obese patient with diabetes mellitus type 2 is the noticeable insulin resistance. Physicians recommended to these patients replace saturated fatty acids and cholesterol by greater dietary monounsaturated fatty acids content, without being absolutely sure about the biochemical mechanisms by which, this change, might help then. It is possible that monounsaturated fatty acids increase sensitivity to the insulin within another mechanism. The following revision is focused in the relationship between the type of dietary fatty acids ingestion and the resistance to insulin in diabetes mellitus type 2 patients.