About Fats, an Introduction

Wet-rendered lard from pork fatback

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

Before we can discuss intelligently about whether saturated fats are good or bad for human health, we must first understand what they are and where they are found.

About Fats (introduction)

Before we can discuss intelligently about whether saturated fats are good or bad for human health, we must first understand what they are and where they are found.    

A fat, in general, is a triglyceride: 3 carbons in a row with a fatty acid attached to each carbon. 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.

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.
  • 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 form of fats when they are stored in fatty tissues or seeds are triglycerides.
  • 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 well as in the cell walls.

In our bodies and those of other animals, they are found in the membranes of every cell and mitochondria. The storage form of fats (as triglycerides) is in the adipose tissue, and to a lesser extent in the liver.

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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