Cis and Trans Fats! What's The Difference?

So it's my first article and I must say that I'm a little excited! Anyway let's get straight to the point, why write about cis and trans fats? Here's why:

• They seem to be a popular topic at the moment
• The majority of people don't know the difference between them
• Artificial trans fats and natural trans fat are very different and need to be identified clearly

To begin understanding cis and trans fats one must first understand the structure of fat in general. Here's a picture of two fatty acids. One of them is saturated and the other unsaturated.

The term ' Saturated' comes from the hydrogen within the fat. If a fat molecule is completely ' Full' with hydrogen it is deemed saturated. Hence why when you have been out in the rain and you are very wet you would describe yourself as being saturated. You are full of water which has hydrogen in it!! But back to the point, the difference between saturated and unsaturated fats is simple. Saturated fats have all of their carbon occupied with hydrogen whereas unsaturated fats do not. They have double bonds and this is clear to see in the diagram above.  If a fat has one double bond like the diagram then it's monounsaturated, if it has more than one double bond it's polyunsaturated.

Now that we have covered the fundamental difference in saturated and unsaturated fats we can move onto cis and trans fats.

Here is the chemical structure of a cis fat:

So what can we see? From the diagram we can see that it's a monounsaturated fat but what else can we see? The red line indicates where the double bond is and the green circles show the hydrogens which are attached to the carbons forming that double bond. These are extremely important in cis and trans fats. In a cis fat the hydrogens attached to the double bond forming carbons are on the same side of the double bond. ' Cis' literally means when two atoms lie on the same side of a given plane. 

This is very important as it gives the molecule a contorted shape. The more cis double bonds you have, the more contorted the shape of the molecule becomes. The shape of the fat molecule is important and will be touched upon later on.

Now let's look at a trans fat:

So straight away we can see the difference. In trans fats the hydrogens attached to the double bond forming carbons are on opposite sides of the double bond. The word ' Trans' means that the two atoms in question ( The hydrogens) lie on opposite sides of a given plane.

So the big question arrives! Why is all of this important? It's all down to molecule shape, the shape and size of a fat molecule determines its melting point. Here are some general guidelines for fat molecule melting points:

• The shorter the fat ( number of carbons) the lower the melting point
• The more cis double bonds, the more contorted the molecule, the lower the melting point

This is important because with small and contorted fat there is less attraction between molecules. This lowered level of attraction causes the melting point to be much lower and so less energy is need to break the fat down. 

Here is a diagram to illustrate the difference in the shape of a cis and trans fat:

The top molecule is the more contorted cis fat and the bottom molecule the trans fat. If you layered these fat molecules on top of one another there would be much less attraction between cis fats. Without going into metabolic processes this is ultimately why cis fats are healthier than trans fats!

From reading this your may be itching to ask a question. When I first came across this type of chemistry I was! The question was this..........Trans fats are unsaturated so why all the bad press? The bad press about trans fats isn't about the naturally occurring trans fats we have discussed here. It's all about the hydrogenated fats that are so widely used in the food industry. Hydrogenated fats are fats that have been forced into saturation. The process involves taking an unsaturated fat, hydrogen gas, a catalyst like nickel and a ton of pressure and forcing the double bonds in the unsaturated fats to break and hydrogen to replace them, thus making the fat saturated. There are several useful functionalities of hydrogenated fats such as turning oils into semi solids but they aren't great for health!

I hope my first article was useful in trying to establish the difference between cis and trans fats!

Ciao.