If two or more double bonds are present, it is a polyunsaturated fat . Our bodies require that certain fatty acids be included in the food we consume. These are called essential fatty acids , because our bodies cannot manufacture them. That's why it is important to consume these fats as part of our diet. Flax seed oil, olive oil, and canola oil are good sources of mono- and polyunsaturated fatty acids.
Butter contains mostly saturated fatty acids.
Fatty acids are used by the body in various ways. They are a primary component of cell walls, for example, and they are used to make hormones and hormone-like substances called eicosanoids that help to regulate various bodily functions. Some studies link saturated fats with an increase in serum cholesterol. However, those studies did not take into account the negative effects of carbohydrates in that equation. Absent carbohydrates, saturated fats have less of an impact on cholesterol.