What are Hydrogenated Fats? - Definition & Examples

Instructor: Sarah Pierce

Sarah has a doctorate in chemistry, and 12 years of experience teaching high school chemistry & biology, as well as college level chemistry.

This lesson introduces hydrogenated fats. Hydrogenated fats are defined, and the chemical reaction used to synthesize hydrogenated fats is discussed. Examples of hydrogenated fats, such as trans fats, are also covered.

Unhealthy Fats

Trans fat is a type of hydrogenated fat that is found in many foods.

Have you heard of trans fats? These fats are the ''bad fats'' found in food that lead to higher levels of the bad cholesterol, which can lead to heart disease. While these can occur naturally, many are a type of hydrogenated fat. Let's find out a little bit more about what trans fats are, how they are made, and why they are bad for you.

What are Hydrogenated Fats?

Hydrogenated fats are fatty acids that have been chemically altered. In general, hydrogenated fats were oils whose chemical structures were changed to become solid fats.

Unsaturated fats have double bonds between carbon atoms, while saturated fats do not have double bonds between carbon atoms.

Saturated fats are saturated with hydrogen atoms, so they have no double bonds between carbon atoms. Unsaturated fats have double bonds.

Unsaturated fats can undergo a chemical reaction, a hydrogenation reaction, that changes their double bonds to single bonds. The unsaturated fat reacts with hydrogen gas in the presence of a metal catalyst, normally palladium, platinum, or nickel. This reaction reduces the number of double bonds in original fat. If just some of the double bonds are turned into single bonds, this is called a partial hydrogenation. If all the double bonds are turned into a single bond, a hydrogenated, saturated fat is formed.


When a fat is hydrogenated, the melting point changes so the fat is now a solid at room temperature. The hydrogenated fat is now easy to spread on a piece of toast. Hydrogenated fats are found in margarine and vegetable shortening.

Oils are used to make hydrogenated fats that are found in the margarine that you put on your toast.

Trans Fats

When an unsaturated fat is hydrogenated, sometimes double bonds can reform. When the bond reforms, it's in a different configuration than the natural fats. Natural fats have a cis double bond, meaning the hydrogen atoms are on the same side of the double bond. An easy way to remember this is to use alliteration: cis, same side.

Cis double bonds have hydrogen atoms on the same side of the double bond.

Trans fats however, have double bonds with the trans configuration, which means the hydrogen atoms are on opposite sides of the double bond.

Trans double bonds have hydrogen atoms on the opposite side of the double bond.

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