Why are fats called 'lipids' instead of 'fats'?
Why are fats called 'lipids' instead of 'fats'?
While the terms "fat" and "lipid" are often used interchangeably in everyday conversation, they have distinct scientific definitions. Understanding the difference requires looking at the scope of these molecules in biological systems.
The Broad Scope of Lipids
Lipids are a diverse group of naturally occurring organic compounds that are insoluble in water (hydrophobic) but soluble in organic solvents. This broad category includes:
- Triglycerides: What we commonly know as fats (solid at room temperature) and oils (liquid at room temperature).
- Phospholipids: The primary building blocks of cell membranes.
- Steroids: Including cholesterol and various hormones.
- Waxes: Protective coatings found in plants and animals.
Why Use the Term 'Lipid'?
The word "lipid" comes from the Greek word lipos, meaning "fat" or "lard." It was coined to serve an umbrella term for all these related hydrophobic molecules.
Calling everything a "fat" would be scientifically inaccurate because a molecule like cholesterol is structurally very different from a stick of butter (a triglyceride), yet both share the characteristic of being lipids.
Summary
In short, all fats are lipids, but not all lipids are fats. Scientists use the term "lipid" when referring to the entire class of these fat-like molecules, reserving "fat" for a specific type of lipid.