**Question:** Which of the following is a byproduct of hydrogenation of vegetable oils?

A. Trans fatty acids
B. Saturated fatty acids
C. Monounsaturated fatty acids
D. Polyunsaturated fatty acids

**Core Concept:** Hydrogenation is a process used to modify the fatty acid composition of vegetable oils. It involves adding hydrogen molecules to unsaturated fatty acids to make them more saturated. Saturated fatty acids have all double bonds converted to single bonds, while trans fatty acids result from partial hydrogenation, maintaining some double bonds in the molecule.

**Why the Correct Answer is Right:** In the process of hydrogenation, vegetable oils undergo partial double bond reduction, which results in the formation of trans fatty acids. Trans fatty acids have the characteristic property of being more stable than their unsaturated counterparts, making hydrogenated oils suitable for frying and shelf-stable food products.

**Why Each Wrong Option is Incorrect:**

A. Saturated fatty acids (e.g., palmitic acid) are not produced by hydrogenation as the process is aimed at increasing the saturation of unsaturated fatty acids.

B. Monounsaturated fatty acids (e.g., oleic acid) are not produced by hydrogenation as the process specifically targets unsaturated fatty acids.

D. Polyunsaturated fatty acids (e.g., linoleic acid) are not produced by hydrogenation, as hydrogenation primarily alters saturated and monounsaturated fatty acids, leaving polyunsaturated fatty acids relatively unchanged.

**Clinical Pearl:** Trans fatty acids, although present in processed foods, are considered less healthy than their natural counterparts (unsaturated fatty acids) due to their association with higher cardiovascular risks. Consuming a diet rich in trans fatty acids can lead to elevated LDL cholesterol levels and decreased HDL cholesterol levels, contributing to an increased risk of heart disease.

**Correct Answer:** D. Polyunsaturated fatty acids

**Explanation:** Polyunsaturated fatty acids are not formed during the hydrogenation process, as hydrogenation primarily targets saturated and monounsaturated fatty acids, leaving polyunsaturated fatty acids relatively unchanged. The process primarily results in the formation of trans fatty acids (option A), saturated fatty acids (option B), and some monounsaturated fatty acids (option C).