Unsaturated fats, both polyunsaturated and monounsaturated, are liquid at room temperature. We typically think of vegetable oils as good sources of polyunsaturated and monounsaturated fats, and low in saturated fats. The exceptions are coconut and palm kernel oils. They contain more than 80 percent saturated fatty acids by weight. Nutritionists recommend that both polyunsaturated and monounsaturated fats be kept at approximately 10 percent of calories.
Vegetable shortenings are a blend of many types of vegetable oils.
The oil becomes solid or firm through the process of hydrogenation. The result is a product that has a lower polyunsaturated fatty acid content and a higher saturated fatty acid content than liquid vegetable oils. Hydrogenation also forms monounsaturated fats that have a different physical arrangement. These trans monounsaturated fatty acids are similar in stability to saturated fatty acids. Research shows their effect on blood cholesterol levels is variable.