You’ve heard that not all fats are created equal, and you know that there are ‘saturated fats’ and ‘unsaturated fats’, which can be ‘mono-‘ or ‘poly-unsaturated’. There are omega-6 and omega-3 fats and even omega-9. And then there are trans-fats, too. But what does it all mean? Read on to find out!
Fats are fairly simple molecules. All of them consist of a chain of carbon atoms (C) with hydrogen atoms (H) attached to them. The first carbon atom is connected to three hydrogen atoms (and the neighbouring carbon); this is called a ‘methyl group’ (CH3). The other end features one carbon, two oxygen and one hydrogen atoms (COOH), which together and connected in this way are an ‘acid group’. This is what makes it a fatty acid.
Saturated vs Unsaturated
Here’s what the chemical structure of a ‘saturated fat’ or ‘saturated fatty acid’ looks like:
All saturated fatty acids look like this, they only vary in length (i. e. the number of carbon atoms in the chain).
An unsaturated fatty acid has at least one double bond. Unsaturated fatty acids lack at least two hydrogen atoms. However, every carbon atom has 4 ‘valences’ – places at which other atoms can form bonds with it. They will not just dangle there empty once hydrogen atoms are missing, but the two carbons will connect to each other by a double bond. Therefore, an unsaturated fatty acid looks like this:
The hydrogen atoms carry an electrical charge, which causes them to repel each other. In a saturated fatty acid the neighbouring and opposite hydrogen atoms ‘push back’, so the chain remains straight. Because of the gap between hydrogen atoms on one side of the unsaturated fatty acid, there is no resistance and the result is a ‘kink’ in the carbon chain. This makes saturated fatty acids straight and rigid, but the kink gives unsaturated fatty acids flexibility. The more double bonds, the more kinks, the more flexible the fatty acid.
Mono-unsaturated vs poly-unsaturated
A fatty acid with one double bond is ‘mono-unsaturated’, those with more than one are ‘poly-unsaturated’
Omega-3 vs Omega-6
The number in the ‘omega’ fatty acid refers to where the first double bond sits: In an omega-3 fat, the first double bond is on the 3rd carbon atom from the methyl end. In an omega-6 fat, it’s on the 6th carbon atom from the methyl end.
Again, all unsaturated fatty acids have the same basic structure, but vary in length of the carbon chain, the number of double bonds, and the placing of the first double bond.
A natural mono- (MUFA) or poly-unsaturated fatty acid (PUFA) usually has a ‘cis-configuration’, meaning that the two ‘missing’ hydrogen atoms are missing from the same side of the carbon chain – allowing the opposite hydrogen atoms to create the ‘kink’.
Another possibility is a ‘trans-configuration’, where one hydrogen atom is missing from one side of the carbon chain and the other from diagonally opposite. This time, there is no ‘kink’, making this fatty acid straight and rigid like a saturated fatty acid, even though it is unsaturated. That’s a ‘trans-fat’.
So there you have it. That's the chemical structure of fats. Understanding it helps understanding the naming of different fatty acids and their different properties (of which you will read in a future blog post).