Saturated Fats, Trans Fats and Unsaturated Fats Explained

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If you are confused about the different kinds of fats there are and what effect they have, this overview will help clarify the issue.

Types of Fat

Several hundred fats have been identified, 20 of which frequently occur in our bodies. They can be categorised according to their molecular composition:

  • Polyunsaturated
  • Monounsaturated
  • Partially saturated
  • Saturated (including trans saturated)

Unsaturated Fat

Unsaturated fats are so called because they have carbon-carbon bonds that could be broken to carry more hydrogen atoms until they are ‘saturated’ with them.

Naturally occurring unsaturated fats contain carbon-carbon bonds that bend the molecule and give it particular properties, such as its flavour and melting point.

Monounsaturated fats contain a single carbon-carbon double bond; fats with multiple carbon-carbon bonds are referred to as polyunsaturated.

unsaturated fat molecule
a monounsaturated fat with one carbon-carbon double bond

Unsaturated fat is more prone to reacting with other elements than saturated fats, and this is perceived as ‘going off’ or becoming rancid.

Partially Saturated Fat

When a polyunsaturated fat undergoes hydrogenation the result can be either a fully saturated or a partially saturated trans fat which has one or more carbon-carbon bonds remaining. From a health point of view, partially saturated fats are similar to saturated fats and should be avoided.

Saturated Fat

A fully saturated fat has no available carbon-carbon bonds that can be converted to carbon-hydrogen bonds. Saturated fats increase your LDL cholesterol.

saturated fat


The process of converting unsaturated fats to saturated fats is called Hydrogenation.

More specifically, it’s a manufacturing process that converts a polyunsaturated or monounsaturated fat into a saturated fat. Where a carbon to carbon double bonds exist, one of the bonds is broken and each of the free ends is reconnected to a hydrogen atom.

In the following diagram, the carbon to carbon double bond bends the molecule:

hydrogenation process
Manufacturing process depicting the conversion of a monounsaturated fat into a fully saturated Cis fat via hydrogenation.

For example, the hydrogenation of vegetable oil converts it from a liquid to a soft solid with a much longer shelf life.

Partial hydrogenation of unsaturated fat converts some of the carbon-carbon bonds into trans fat versions. The molecule has exactly the same atoms in a different arrangement – for example, a shape that is a mirror image of one found in nature. Partial hydrogenation will yield a trans fat.

Trans Fats and Cis Fats

The configuration of carbon-carbon bonds is affected by the positions of the hydrogen-carbon bonds that are present. Carbon-carbon bonds are naturally made on the same side of the atom, resulting in a molecule that has a bend in it, this is the Cis configuration found in naturally occurring fats.

A trans fat that has been created during hydrogenation has a carbon-carbon bond from opposite sides of the carbon atom, resulting in a straighter fat molecule, changing its melting point, shelf life, flavour and stability. Unfortunately, the changed molecular shape makes it difficult for your body to manage and remove. Trans fats are created by partial hydrogenation.

Fats and Health

  • For good health, your body needs unsaturated fats to build and repair cell walls.
  • Bad health is promoted by an excess of saturated fats that change your LDL and HDL cholesterol balance. Increased LDL cholesterol may lead to deposits on the walls of arteries and veins which can lead to a heart attack or stroke.
HDL & LDL choleseterol

For a healthy person, the total cholesterol should be less than 5 millimoles per litre, with LDL less than 3 and HDL more than 1.

Eating foods that contain cholesterol will not raise your cholesterol level unless your body needs it. Ingesting trans-fat and saturated fat will increase blood cholesterol, but the level you have depends upon a combination of factors:

  • whether you are male or female
  • your genes and ethnicity
  • your age
  • medical history
  • smoking – promotes deposition of cholesterol
  • diabetes – via high blood sugar
  • poor diet
  • excess weight
  • a sedentary lifestyle

You can help by controlling the intake of saturated fats in foods such as:

  • Butter and lard
  • Processed Meats
  • Sausages
  • Pies
  • Full fat milk
  • Creams and ice cream
  • Cheese
  • Coconut oil, coconut cream and palm oil
  • Biscuits, cakes and pastries
  • Chocolates and some sweets


Whilst there are essential fats that we must have in our diets, most of the fats we ingest don’t do us a lot of good and we eat far too much of it. It builds up in the arteries and causes problems. Old and new theories both name trans fats as the top priority food ingredient that requires caution. If the food label includes ‘hydrogenated’ in the list, it’s probably a trans fat.



Care has been taken to keep the information in this article as accurate as possible but errors are possible, so be aware of the full disclaimer here.