Unsaturated fat

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An unsaturated fat has at least one double bond in its fatty acid chain. If there is one double bond, it’s monounsaturated; if there are two or more, it’s polyunsaturated. A saturated fat has no double bonds and is fully saturated with hydrogen.

In metabolism, unsaturated fats provide slightly fewer calories than the same amount of saturated fats. The more double bonds a fatty acid has, the more prone it is to oxidation (rancidity). Antioxidants like vitamin E help protect unsaturated fats from this damage.

Chemists analyze fats by breaking them into fatty acids. One common approach makes fatty acid methyl esters (FAMEs) for measurement by gas chromatography.

Examples of unsaturated fatty acids include oleic acid (monounsaturated), and linoleic, linolenic, and arachidonic acids (polyunsaturated). Others are palmitoleic and myristoleic acids. Foods rich in unsaturated fats include avocado, nuts, olive oil, and other vegetable oils such as canola. Meats contain both saturated and unsaturated fats.

Health guidance often suggests that unsaturated fats should not exceed about 30% of daily calories. Most foods contain both unsaturated and saturated fats, and marketing sometimes highlights only one type.

In cell membranes, mammals and birds typically have more polyunsaturated fats than reptiles, making membranes more fluid but more costly to maintain. This may relate to higher metabolic rates in warm-blooded animals. In very cold environments, fish increase membrane unsaturation to keep membranes flexible.

Overall, unsaturated fats are generally considered healthier than saturated fats when used to replace them, but balance and overall diet matter.