Are Lipids Also Called Fats and Oils?

January 3, 2026 •

4 min read

According to the National Institutes of Health, lipids are a broad class of compounds that are insoluble in water, and this diverse group includes more than just fats and oils. The terms are not interchangeable, but are part of a larger biological hierarchy that impacts human health, nutrition, and cell function.

Quick Summary

Lipids are a broad category of organic molecules, which include fats and oils as specific subgroups. All fats and oils are lipids, but not all lipids are fats or oils. The primary distinction lies in their chemical structure and physical state at room temperature, with fats being solid and oils being liquid.

Key Points

Hierarchical Relationship: All fats and oils are lipids, but not all lipids are fats or oils.
State at Room Temperature: Fats are solid at room temperature, while oils are liquid.
Chemical Structure: The solid state of fats is due to saturated fatty acids, while the liquid state of oils is due to unsaturated fatty acids.
Broader Category: The lipid category includes not just fats and oils, but also waxes, steroids (like cholesterol), and phospholipids.
Biological Function: Lipids are essential for energy storage, insulation, forming cell membranes, and acting as hormones.
Dietary Distinction: Understanding the difference helps make healthier dietary choices, as saturated and unsaturated fats have different health impacts.

What Exactly Are Lipids?

Lipids are a diverse group of naturally occurring organic compounds that are soluble in non-polar organic solvents but largely insoluble in water due to their hydrophobic nature. These macromolecules are crucial for various biological functions, including long-term energy storage, providing insulation, forming structural components of cell membranes, and serving as signaling molecules. The lipid family is expansive and includes several different classes of molecules, such as:

Fatty Acyls: The building blocks of many complex lipids.
Glycerolipids: This category includes fats and oils, which are technically known as triglycerides.
Glycerophospholipids: Key components of all biological membranes.
Sterol Lipids: Includes important molecules like cholesterol and steroid hormones.
Waxes: Act as protective coatings in plants and animals.

The Relationship Between Lipids, Fats, and Oils

To clarify the common confusion, think of it as a hierarchy. 'Lipid' is the umbrella term, and 'fats' and 'oils' are specific, well-known subcategories under that umbrella. The key difference between fats and oils is their state at room temperature, which is determined by their chemical composition, specifically the saturation of their fatty acid chains.

Fats: Fats are a type of lipid called triglycerides that are solid at room temperature. This is because they are composed primarily of saturated fatty acids, which have no double bonds in their hydrocarbon chains. The straight shape of saturated fatty acids allows them to pack tightly together, resulting in a solid state. Animal fats, like butter and lard, are classic examples.
Oils: Oils are also triglycerides, but they are liquid at room temperature. Their liquid state is a result of their high content of unsaturated fatty acids, which contain one or more double bonds. These double bonds create "kinks" or bends in the fatty acid chains, preventing the molecules from packing together tightly and thus remaining liquid. Most plant-based oils, such as olive and sunflower oil, fall into this category.

Functions and Significance

Beyond simple energy storage, the different types of lipids play unique and vital roles within living organisms.

Energy Storage and Insulation The most well-known function of fats and oils is energy storage. They provide a dense, long-term energy reserve for both plants and animals. In animals, fats are stored in adipose tissue, which also provides thermal insulation and protective cushioning for vital organs. This is particularly important for animals in cold climates.

Structural Components Phospholipids are a crucial type of lipid that forms the lipid bilayer, the fundamental structural component of all cell membranes. This bilayer acts as a selective barrier, controlling which substances can enter and exit the cell. The unique hydrophilic (water-loving) head and hydrophobic (water-fearing) tail structure of phospholipids is essential for this function.

Chemical Messengers Steroids, another class of lipids, act as vital chemical messengers. Cholesterol is a precursor for several steroid hormones, including sex hormones like estrogen and testosterone, and stress hormones like cortisol. These hormones regulate a wide range of physiological processes.

Nutritional Impact and Health

Understanding the distinction between different lipids is critical for making informed dietary choices. Saturated fats (like those in butter and red meat) have long been associated with potential health risks, while unsaturated fats (like those in olive oil and avocados) are generally considered beneficial for heart health. However, it is the broader context of lipids that is most important. Cholesterol, for example, is a sterol lipid that plays a key role in cardiovascular health, and phospholipids are necessary for cellular integrity. A balanced diet should include a variety of lipids, emphasizing unsaturated sources while moderating saturated and avoiding unhealthy trans fats.

A Comparison of Lipids, Fats, and Oils


Feature	Lipids	Fats	Oils
Definition	A broad, diverse class of biomolecules.	A type of lipid (triglyceride) that is solid at room temperature.	A type of lipid (triglyceride) that is liquid at room temperature.
Composition	Diverse; includes fatty acids, steroids, phospholipids, etc.	Primarily saturated fatty acids.	Primarily unsaturated fatty acids.
State at Room Temp.	Varies (solid, liquid, waxy).	Solid.	Liquid.
Examples	Cholesterol, phospholipids, waxes, butter, olive oil.	Butter, lard, fat in red meat.	Olive oil, sunflower oil, corn oil.
Biological Role	Energy storage, structural components, signaling.	Long-term energy storage, insulation.	Long-term energy storage, source of essential fatty acids.

Conclusion

In summary, while the terms 'lipids', 'fats', and 'oils' are often used interchangeably in casual conversation, they have distinct and important scientific meanings. Lipids are a large, overarching category of organic molecules defined by their hydrophobic nature. Fats and oils are specific types of lipids known as triglycerides, differentiated primarily by their physical state at room temperature. Fats are solid due to their saturated fatty acid content, while oils are liquid because of their unsaturated fatty acids. This hierarchical understanding is vital for grasping the roles these molecules play in biology and their impact on nutrition and health. Acknowledging these differences allows for a more precise and informed discussion of biochemistry and diet.

Explore more about the role of lipids in human health on the National Institutes of Health website.

Frequently Asked Questions

The main difference is their physical state at room temperature. Fats are solid, while oils are liquid. This is due to their differing levels of saturation in the fatty acid chains.

No, you cannot. 'Lipid' is a broad category of molecules, and 'fats' are just one specific type of lipid (triglycerides). While all fats are lipids, not all lipids are fats.

Oils are liquid because they contain a higher proportion of unsaturated fatty acids. These fatty acids have double bonds that cause bends in their chains, preventing tight packing. Fats, with their straight-chained saturated fatty acids, can pack more tightly, making them solid.

Yes, phospholipids, which form cell membranes, and steroids, such as cholesterol and hormones, are all different classes of lipids.

Lipids have several vital functions in the body. They serve as a long-term energy reserve, provide thermal insulation, form the structural components of cell membranes, and act as chemical messengers (hormones).

No. While some types, like trans fats, are unhealthy, many lipids, including essential fatty acids and those found in healthy oils, are necessary for proper bodily function and a balanced diet.

Fats are primarily stored in specialized cells called adipocytes, which make up adipose tissue. This tissue is located under the skin and around internal organs.