Final answer:
Hydrogenation is the chemical process of adding hydrogen to unsaturated plant oils, often resulting in the formation of unhealthy trans fats which can increase bad cholesterol levels and the risk of heart disease.
Step-by-step explanation:
When unsaturated plant oils are hydrogenated, hydrogen gas is introduced to the oil in the presence of a catalyst such as nickel, platinum, or palladium. This process adds hydrogen atoms to the oil, converting unsaturated fatty acids with double bonds into saturated fatty acids with single bonds. The hydrogenation process can be either partial or complete, with partial hydrogenation often leading to the formation of trans fats.
Consuming products with hydrogenated oils can lead to health problems. Partial hydrogenation causes the conversion of some cis double bonds into trans double bonds, which unlike the naturally occurring cis fats, are linear in shape. This unusual shape of trans fatty acids makes them act similarly to saturated fats in the body, leading to an increase in low-density lipids (LDL), which is considered bad cholesterol and is associated with an increased risk of heart disease.
Therefore, while hydrogenation increases the shelf life and stability of vegetable oils, producing desirable semi-solid fats like margarine and shortening, it also introduces trans fats into the diet, which can have detrimental effects on cardiovascular health.