What are lipids?
Lipids is a broad category that describes a group of about 7,000 fat-soluble, hydrophobic (not soluble in water) and naturally occurring organic compounds, found in animal or plant tissues.
Fatty acids are chains of hydrocarbons – chains of carbon atoms, with each of the carbon atoms connected to one or two hydrogen atoms.
Fatty acids can be saturated or unsaturated:
- Saturated fatty acids have a straight shape. Since they are straight, they stick together closely. Therefore, their force of attraction is stronger.
- Unsaturated fatty acids (either mono or poly-unsaturated) have a sharply bent structure, where the carbon double-bonds are positioned. This is called a “cis” configuration. (read more..).
Due to this uneven structure, these fatty acids can’t pack together as closely as saturated fatty acids. Therefore, the attraction forces are not as strong, resulting in a lower melting point.
The more kinks there are along the chains, the lower is the molecular attraction and, consequently, the lower is melting point. Polyunsaturated fatty acids, with more “cis” double bonds, have a lower melting point than those with less.
NOTE: one exception to this rule is with trans fatty acids. In trans fatty acids, some of the carbon double bonds have a “trans” configuration. This causes a slight kink, instead of a sharp angle as in the “cis” configuration.
If all of the carbon double bonds in the chain have a trans configuration, the fatty acid chains become more or less straight. In this case, they resemble saturated fatty acids, not only in shape but also in properties, such as solidity at room temperature.
What are fats and oils?
Triglycerides consist of three fatty acids – another subgroup of lipids. They are all attached to another component, that holds them together, the glycerol backbone.
A triglyceride can contain any combination of fatty acids (such as one saturated and two unsaturated or three saturated or three unsaturated, or one unsaturated and two saturated).
The combinations of fatty acids in fats and oils vary greatly. The same is true with their properties, such as their melting points.
Fats and oils can be either of animal or plant origin.
The following is a simplified image of how fats relate to lipids.
What are the differences between fats and oils?
Fats refer to lipids that are solid at room temperature (have a high melting point). They are solid, mainly because they have a higher proportion of saturated or trans fatty acids and their hydrocarbon chains are long. For more details on fats’ melting points, read here.
Oils, in a nutritional sense, refer to lipids that are liquid at room temperature (have a low melting point). Similar to fats, oils mainly consist of triglycerides. However, unlike fats, the predominant fatty acids in those triglycerides are unsaturated, which make them liquid at room temperature.
Although some oils can be non-edible, such as petrochemical products, in the nutritional context, they refer to edible oils that are mainly of plant origin, but also of animal origin (e.g. fish oil). (3, 4, 2)
NOTE: coconut oil is primarily made up of saturated fatty acids, unlike other oils. However, most of these fatty acid chains are shorter (called medium chain fatty acids – MCFAs) than those of solid fats, such as in butter (long chain fatty acids – LCFAs).
MCT oil, however, is in a liquid form even though it is also (like coconut oil) made up of MCTs. The reason is that the MCTs in MCT Oil are shorter than in coconut oil (short enough to be liquid). (read more..)
Therefore, its melting point is low, which explains why coconut oil becomes liquid, if the room temperature is slightly higher.
In this case, the length of the fatty acid chains has more impact on the solidity than the level of saturation. (6)