Fatty acids are chemically modified by adding hydrogen. The process of hydrogenation creates fats which act somewhat like saturated fats in the body and is associated with greater plaque build-up. Shortening (and foods made with shortening) and stick margarine are examples of fats. Other ways to prevent spoilage are to add antioxidants, such as vitamins, or to add BHA or BTA to the item.
Fats added to foods during preparation or at the table are a major source of fat in the diet. Fats may be visible on foods, such as the fat trimmed from steak, or they may be invisible, such as the fat in biscuits or olives.
Less than 35% of the total calories should come from fat, specifically about 0% from MUFA, less than 0% from PUFA, 7% from saturated fats, and definitely less than from trans-fat.
Fat is part of the cell membrane, insulates the body, protects organs, and is a backup energy source (1g yields calories).