Food manufacturing companies create hydrogenated oils by adding hydrogen atoms to the fat that they use. Partially hydrogenated oils are found in many commercially available food products from peanut butter to pies and from vegetable shortening to cream-filled pastries. This hydrogenation process has both advantages and disadvantages, because it has a dramatic impact on the fats and their physical properties.
Partially hydrogenated oils, and hydrogenated oils and fats offer improved shelf life compared to liquid vegetable oils and other types of fat. Foods containing these partially hydrogenated oils also benefit from longer shelf lives. In their unhydrogenated state, these foods would become rancid more quickly and would not last as long on the grocer's shelves. Some food items, like peanut butter and shortening, can actually last for several years.
Saturated and Trans-Saturated Fats
When unsaturated fats in vegetable oils are partially hydrogenated, the unsaturated fats become increasingly saturated. The presence of partially hydrogenated oils in commercially available foods has raised the presence of saturated and trans-saturated fats in your diet. Trans-saturated fatty acids are present in some foods naturally, but only on a very small scale. The trans-saturated fats found in partially hydrogenated oils are in much larger quantities than is natural. Diets that are high these fats increase the risk of heart disease and other health issues.
Partially hydrogenated fats improve the texture in some foods. For example, tub margarine products made using partially hydrogenated vegetable oils are creamier and smoother to spread than stick margarine or butter. Vegetable shortening, also made with partially hydrogenated oils, is what lends the desirable flaky texture to commercial piecrusts. The improvement in texture offered by partially hydrogenated oils is one of the reasons these oils were developed in the first place, as they have made many commercial food items more palatable.