Which type of fatty acid is most stable?

• A. Saturated.
• B. Polyunsaturated.
• C. Monounsaturated.
• D. Trans fats.

Answer: (A)

Stability of fats is largely about resistance to oxidation. Oxygen tends to attack carbon–carbon double bonds, so the more double bonds a fatty acid has, the more sites there are for oxidative damage and rancidity. Saturated fatty acids have no double bonds, which means there are no reactive sites for oxygen to attack, making them the most stable structure under heat and air and giving them longer shelf life. Monounsaturated fats have one double bond, making them more prone to oxidation than saturated fats, while polyunsaturated fats have many double bonds and oxidize most readily. Trans fats contain double bonds as well, but their trans geometry makes the chain more linear and can offer somewhat more resistance to oxidation than cis-unsaturated fats, yet they’re still less stable than fully saturated fats. So, the most stable fatty acid type is saturated.