Lipids: Essential Energy-Supplying Nutrients
Fats and oils are forms of a larger and more diverse group of substances
called lipids; most lipids are insoluble in water.
The three types of lipids commonly found in foods are triglycerides,
phospholipids, and sterols.
Most of the fat we eat is in the form of triglycerides; a triglyceride is a
molecule that contains three fatty acids attached to a glycerol backbone.
The various fatty acids in triglycerides are classified based on chain length,
level of saturation, and shape.
Short-chain fatty acids are usually fewer that six carbon atoms in length;
medium-chain fatty acids are six to twelve carbons in length, and long-chain
fatty acids are 14 or more carbons in length.
Saturated fatty acids have no carbons attached together with a double bond,
which means that every carbon atom in the fatty acid chain is saturated with
Monounsaturated fatty acids contain one double bond between two carbon
atoms; monounsaturated fatty acids are usually liquid at room temperature.
Polyunsaturated fatty acids contain more than one double bond between
carbon atoms, and these fatty acids are also liquid at room temperature.
Saturated fats are straight in shape, allowing the fatty acid chains to pack
tightly together and making them solid at room temperature.
Unsaturated fats (those with one or more double bonds in their fatty acid
chains) have a kink along their length which prevents them from packing
tightly together and results in their being liquid at room temperature.
A cis fatty acid has hydrogen atoms located on the same side of the double
bond in an unsaturated fatty acid. This cis positioning produces a kink in the
unsaturated fatty acid and is the shape found naturally occurring fatty acids.
A trans fatty acid has hydrogen atoms located on opposite sides of the double
carbon bond. This positioning causes trans fatty acids to be straighter and
more rigid, like saturated fats. This trans positioning results when oils are
hydrogenated during food processing.