The Chemistry of Fat
There is a great deal of debate, controversy and questions surrounding the topic of the amount and types of fat the constitute a healthy diet. There are so many mixed messages about so-called "good" fats, "bad" fats, saturated and unsaturated fats, plant and animal fats. But what does it all mean? A wise and healthy friend recently asked me to explain the difference between saturated and unsaturated fats to her, in terms of chemistry and what happens in the body. She is very knowledgable about nutrition and knew that unsaturated plant and vegetable oils are bad news and good fats like coconut oil, organic butter and avocados (which all naturally contain saturated fats) are good for you. After I finished explaining the chemistry of these fats, she said I should write a post about it and so that's exactly what I am going to do.
Chemistry has been my favourite subject at school for the past three years and I achieved a perfect Year 12 score in Chem last year (much to my delight). So whilst I am in no way overly qualified as a chemist, I know a thing or two about the structure of fats. I will do my best to explain this all in simple, easy-to-understand English.
The Difference between Saturated and Unsaturated Fats
All fats and oils fall under the umbrella of triglycerides, which basically means they are consist of three organic fatty acid chains connected to a glycerol base (glycerol is a type of organic alcohol). The saturated or unsaturated refers to the chemical structure of the fatty acid chains attached to the glycerol. In a saturated fat all the carbon atoms are joined together by single carbon-carbon bonds and are therefore "saturated" with hydrogens, meaning the carbons are bonded to the maximum possible number of hydrogen atoms. However, in "unsaturated" or "polyunsaturated" (as in polyunsaturated plant oils) fats there are at least two carbon-carbon double bonds. This means these carbon atoms are sharing an extra pair of electrons between them than they normally would. As a result, the chain of carbons is unsaturated, as it is not bonded to the maximum number of hydrogen atoms.
To understand this, look at the diagram below:
The aqua part on the left hand side is the glycerol base, it is the same in all fats. The red parts are the ester bonds joining the fatty acids (black) to the glycerol base. The black chains of carbon (C) and hydrogen (H) are the fatty acids. The top two fatty acid chains are saturated, as they contain only single (black) bonds between carbon atoms. The bottom chain shows a carbon-carbon double bond (green) and is therefore unsaturated. In this particular diagram the fatty acid is "monounsaturated" because it only has one double bond in the chain. Generally speaking the plant and vegetable oils (except olive oil) are polyunsaturated fats, meaning they have many double bonds.
So you've got that right? Makes sense?
How Saturated and Unsaturated Fats React
Saturated fats are the more stable than unsaturated fats, meaning they are less reactive. This is because when some other little molecule comes along who wants to react with a fatty acid, it first needs to find a place react. Imagine, if you will, a circle of children in the school yard. In a saturated the children all sit together in a tight circle and there are no gaps anywhere, so the new child who is trying to join the circle (the reactant molecule) finds it very hard to find a place in the circle to sit. In an unsaturated fat the children sit together in a circle, but wherever there is a double bond there is a gap in the circle. Now, the child trying to join the circle can see this gap and very easily slides into the circle. So basically, unsaturated fats will react more easily because the double bond provides a "target" point for the reactant molecules to react with.
What Saturated and Unsaturated Fats Do in Your Body
So now that you understand the basic structural difference of these two types of fats, and how they react, we can move on to what this means for your body and your health. Every cell in your body (we have trillions of them) has a cell membrane, which (surprise, surprise) is made of fats. These fats are called phospholipids, and are similar to the triglycerides above, but they have two fatty acid chains and one phosphate group instead of a third fatty acid chain. And where do these phospholipids come from? Well, when you eat anything containing fat, the fatty acids and glycerol are separated during digestion and absorbed into the body. Then phospholipids are synthesised in specialised parts of the cell, using the fatty acids collected from the food you ate. So if you eat unsaturated fats, you will have more unsaturated fatty acid molecules in your phospholipids and vice versa.
So these phospholipids then go on to make up the cell membrane of all the cells in your body. The cell membrane is crucial in maintaining cellular health and also regulating cell division. So it is important to have strong, well functioning cell membranes. If your cell membranes are made up of saturated fats, they are likely to be very healthy, because they are less likely to react with other molecules in the body, such as "free radicals". What are free radicals I hear you ask? They are uncharged molecules that are highly reactive. They cause oxidative reactions in your body and are neutralised by antioxidants (in all your good fruits, veggies, nuts and seeds).
So these free radicals, imagine them zooming around your body like children on red cordial. They want to cause damage and wreak havoc. They want to disturb as many groups of children as possible. So if your cell membranes contain a high proportion of unsaturated fats (circles of children with gaps), these free radicals have a target spot and they can easily react with the unsaturated fats, ultimately altering their structure and function. On the contrary, if your cell membranes are made of saturated fats, the crazy free radical child runs around but cannot disturb or upset the tightly-packed circles of children in the school yard.
So unsaturated fats in the cell membranes are more vulnerable to free radical oxidative damage? Yes. And what does that mean for your health? Well, disease, and in particular cancer, is a result of faulty cells and cell regulation. The oxidative reactions of unsaturated fats in the cell membrane increases the chance of cancerous cells appearing, by reducing the effectiveness of the control regulations placed upon cell divisions.
Long story short, unsaturated fats = cancer, heart disease and more.
Saturated fats = strong cell membranes and reduced risk of disease.
What You Should and Shouldn't Eat
Do Eat: healthy saturated and monounsaturated fats found in coconut oil, coconut cream and coconut milk, avocados, raw nuts and seeds, olive oil, organic grass-fed butter, eggs, grass-fed animal protein.
Don't Eat: polyunsaturated plant seed oils - canola oil, sunflower oil, "vegetable" oil of any kind, low-fat/fat-free products of any kind, processed foods (they almost always contain bad, unsaturated vegetable oil), margarine.
Keep healthy and keep eating saturated fat!
Used to assist in writing this article: http://www.abc.net.au/local/stories/2013/03/06/3708514.htm