About Fats, an Introduction

Wet-rendered lard from pork fatback

By Cat, December 2006; updated April 2019 (Photo, right, from Wikimedia Commons)

Many of us are afraid of fats and fatty-foods in our diet, especially saturated fats. This fear is mostly unfounded (partially-hydrogenated trans-fats are an exception and are known to be harmful). Did you know that the membranes of each and every one of our cells and mitochondria are comprised mainly of fatty acids, the main component of fats)?

About Fats (introduction)

Fats are a major group of biochemicals called “lipids,” which means they are not water soluble.  There are three basic categories of lipids:

  • Glycerides, which are comprised of one to three fatty acids bound to a glycerol backbone (a chain of 3 carbons with an alcohol group attached to each). More on this, below.
  • Phospholipids, which are mainly comprised of of fatty acids (not water-soluble) bound to a phosphorous group (water-soluble). They form the majority of our cell membranes, with the fatty acids on the inside of the cell and the phosphorous group on the outside of the cell.
  • Steroids, which include hormones and cholesterol. Did you know that vitamin D is made from cholesterol, using energy from the sun?

Note that the terms “fats” and “fatty acids” are often used interchangeably in discussions; however fatty acids are found in both “fats” (glycerides) and phospholipids.


As explained above, a glyceride is 3 carbons in a row with a one to three fatty acids attached. I like to explain this with an analogy:

First, the glycerol backbone:

  • It is like a coat rack made from a board on your wall with 3 coat hooks attached, and each hook has a coat hanging from it;
  • The board and empty hooks are like the “glycerol backbone:” 3 carbons in a row (the board), each with an alcohol (OH) group attached (the empty hooks).

Second, the fatty acids:

  • These are represented by the coats in the analogy.
  • A fatty acid is a chain of hydrocarbons (hydrogens and carbons) with an acidic carboxyl group (COOH in chemistry composition) at one end.  These fatty acids are represented by the coats in the analogy. When a fatty acid attaches to one glycerol carbons:
    • the H (of the COOH at the end of the fatty acid) combines with an OH (alcohol group) on the glycerol backbone to form a molecule of water (H2O or HOH), and
    • the rest of the fatty acid binds to the carbon on the glycerol backbone from which the OH was removed.

Third, the glycerides:

  • A glyceride may have 1, 2, or 3 fatty acids attached. They react with the alcohol groups on the glycerol backbone to make a glyceride plus water, as described above.
  • One coat on a hook, is like a mono-glyceride; two coats, each on its own hook, is like a di-glyceride; three coats, each on its own hook, is like a tri-glyceride. the storage form of fat in adipose tissue of animals, or in the seeds of plants.
  • The fatty acids in a glyceride can be all of the same type, or each can be different. The specific fatty acids give different fats their unique characteristics.

In a cooking fat such as butter, lard, olive oil, or vegetable oil, the triglycerides are all different in their composition, but collectively, they give the fat its basic characteristics. For example:

Lard, which is considered a saturated fat because it is solid at room temperature, actually has more unsaturated fatty acids than saturated: it’s fat composition is 30% saturated fat, 45% monounsaturated fat (the so-called ‘good fat’), and 11% poly-unsaturated fats. (13)

Saturated vs un-saturated fatty acids

Saturated fatty acids are a type of natural fat found mostly in animals and tropical plants (such as palm and coconut).  They are solid at room temperature, but melt upon warming or heating.  They do not readily become rancid, because they contain no reactive double bonds.  Their molecules are straight (columnar), but not rigid.  This straightness gives stability to cell membranes, but they have enough flexibility that they can respond companionably to their surroundings.

Unsaturated fatty acids, by contrast, are found both in animals and plants, and are liquid at room temperature.  They contain one or more double bonds, which makes them more vulnerable to rancidity, and give them kinks in their molecular structure.   The structural kinks provide a lot of give and take or elasticity in their response to their surroundings, much like a spring.

  • Mono-unsaturated fatty acids have one double bond in the carbon chain.
  • Poly-unsaturated fatty acids have more than one double bond.

Man-made partially hydrogenated trans fatty acids (made synthetically from poly-unsaturated vegetable oils), are also solid at room temperature and melt upon heating. But like other poly-unsaturated fats, they contain more than one double bond, and become rancid more readily than saturated fats (they are more readily oxidized).  The trans configuration of the double bonds makes their molecules extremely rigid and unforgiving to changes in their surroundings, such as when incorporated into cell membranes. Fats including these man-made fatty acids are now known to be harmful to our health.

Where fats are found

In plants, they are mainly found in seeds (as triglycerides or storage fat), as well as in the cell walls.

Similarly, in humans and other animals, they are found in adipose and liver tissue (storage fat), and also in the membranes of every cell and mitochondria.

An interesting fact that most people don’t know, is that most body fat (storage fats) is made in the liver from excess carbohydrates and proteins, and not from dietary fats. This process is triggered by excess insulin in the blood.

See also:

  • How fat is stored & burned as energy in the human body (2).
  • Body Fat Storage and Insulin: How They Affect Diabetes Management (3).

Common Saturated Fats and Fatty Acids

See Saturated Fats.


  1. Cat’s background in chemistry and molecular biology.
  2. healthyliving.azcentral.com/fat-stored-burned-energy-human-body-15876.html
  3. inbodyusa.com/blogs/inbodyblog/body-fat-storage-and-insulin-how-they-affect-diabetes-management/

About Cat

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