Difference between lipids, fats and oils

Difference between lipids, fats and oils

Pawel Malczewski
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Short summary

The terms lipids, fats and oils are often confused. This article explains the differences between those terms and how they relate to each other. For a quick answer click here.

Explanation

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.

Lipids include compounds such as fatty acids, cholesterol, lipoproteins, phospholipids, steroids, waxes and even fat soluble vitamins.

One of the subcategories of lipids, the fatty acids, is crucial to understand the differences between fats and oils. (1)Subramaniam S, Fahy E, Gupta S, Sud M, Byrnes RW, Cotter D, et al. Bioinformatics and Systems Biology of the Lipidome. Chem Rev. 2011 Oct 12; 111(10): 6452–6490. Available here. (2)Klein DR. Organic Chemistry. 2nd Edition. Available here.

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.

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?

Fats and oils are substances that belong to a lipid subgroup called glycerides, specifically triglycerides. (3)FAO. Food and agriculture organization of the United States. Definitions and classifications of commodities. 14. Vegetable and animal oils and fats. Available here. (4)O’Brian R. Fats and Oils: Formulating and Processing for Applications. 3rd Edition. Available here. (5)Klein DR. Organic Chemistry. 2nd Edition. Available here. (6)Berg JM, Tymoczko JL, Stryer L. There Are Three Common Types of Membrane Lipids. Biochemistry. 5th edition. New York: W H Freeman; 2002. Section 12.3. Available here.

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.

Lipid categories

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). (7)FAO. Food and agriculture organization of the United States. Definitions and classifications of commodities. 14. Vegetable and animal oils and fats. Available here. (8)O’Brian R. Fats and Oils: Formulating and Processing for Applications. 3rd Edition. Available here. (9)Klein DR. Organic Chemistry. 2nd Edition. Available here.

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) than those of solid fats, such as in butter. 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. (10)Institute of Shortening and Edible Oils. Food fats and oils. Tenth Edition. Available here.

Conclusion

Back to top

Lipids include a wide range of non-water soluble compounds. Fats and oils belong to a subgroup of lipids, called glycerides, and consist of three fatty acids and a glycerol backbone. Fatty acids are another subgroup of lipids, built of hydrocarbon chains and can be saturated or unsaturated.

Fats are composed of triglycerides, with predominantly saturated or trans fatty acids, with long chains, making fats solid at room temperature.

Oils are composed of triglycerides, with predominantly unsaturated fatty acids. They are liquid at room temperature.  They are mainly unsaturated, often consisting of polyunsaturated fatty acids. Even if the fatty acid chains are long, this will not make them solid.

References   [ + ]

1. Subramaniam S, Fahy E, Gupta S, Sud M, Byrnes RW, Cotter D, et al. Bioinformatics and Systems Biology of the Lipidome. Chem Rev. 2011 Oct 12; 111(10): 6452–6490. Available here.
2. Klein DR. Organic Chemistry. 2nd Edition. Available here.
3. FAO. Food and agriculture organization of the United States. Definitions and classifications of commodities. 14. Vegetable and animal oils and fats. Available here.
4. O’Brian R. Fats and Oils: Formulating and Processing for Applications. 3rd Edition. Available here.
5. Klein DR. Organic Chemistry. 2nd Edition. Available here.
6. Berg JM, Tymoczko JL, Stryer L. There Are Three Common Types of Membrane Lipids. Biochemistry. 5th edition. New York: W H Freeman; 2002. Section 12.3. Available here.
7. FAO. Food and agriculture organization of the United States. Definitions and classifications of commodities. 14. Vegetable and animal oils and fats. Available here.
8. O’Brian R. Fats and Oils: Formulating and Processing for Applications. 3rd Edition. Available here.
9. Klein DR. Organic Chemistry. 2nd Edition. Available here.
10. Institute of Shortening and Edible Oils. Food fats and oils. Tenth Edition. Available here.

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