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The problem of trans fats

There appears to be a lot of confusion about the role of fats in our diet. I've been very confused myself, and it was only when I started doing the research that led to this article that the fog started to lift. We've heard about saturated and unsaturated fats, hydrogenated fats, mono and poly unsaturates, and more recently trans-fats. For many years fat has been regarded as the enemy, and dairy products such as butter were seen as a sure route to a heart attack. We were encouraged to eat margarine because it was supposed to be healthier - this is one particular nutritional falsehood that I didn't fall for, after seeing the chemical processes that are used to make it. 

Unfortunately this confusion has led to some very peverse results. We're constantly being advised to eat a low-fat diet, there are low-fat products everywhere you look, so how is it that we're not getting any thinner? 

The explanations are there in the scientific literature, the right information is not that hard to find, but I'm still seeing misleading advice and flawed research appearing on a regular basis. To become resilient with your health you have to become an educated consumer and make your own decisions. To do this you need to understand a bit of the science, which is not everyone's cup of tea - if this was your least favourite subject please stick with me, as I'm going to do my best to explain the significance of fats in some detail.


Our bodies are made up of cells, and our cells have sub-cellular components - a nucleus to contain the genetic material, mitochondria for energy, and various structures for making proteins, transporting materials and dealing with waste. The contents of the cell is largely liquid, but it is surrounded by a membrane called the plasma membrane, as are the sub-cellular structures too. 

Plasma membranes

Plasma membranes are extremely important to our cells and therefore to our health. They have to be strong enough to protect the cells from foregn invaders, yet flexible enough to allow the cell to move. They permit nutrients to enter, while acting as a barrier to unwanted substances. In our nerve cells they display amazing electrical properties which makes it possible for the nerves to transmit electrical signals.  The correct functioning of these membranes is essential for our cells to produce energy, fight disease, and manufacture the raw materials of life.

Fatty acids

The basic building blocks of plasma membranes are fatty acids, which come from the fats that we eat in our diet. Some can be manufactured in our bodies from other substances such as glucose, but there are others that cannot be made by our cells, so have to be taken in through the food we eat.

Fatty acids have a backbone of carbon atoms joined together by chemical bonds, and it is these bonds that determine the type of fat we're dealing with. Carbon to carbon bonds in fats can be single or double, and the double bonds have two variants - cis and trans. It is this last type of bond - the trans double bond - that gives rise to the label "trans-fats" that you may have heard about.

The diagram below shows "ball and stick" models of these three bond types. The grey balls represent carbon atoms and the smaller white balls represent hydrogen atoms. The lines joining them are chemical bonds. Bear in mind that these are just representations - at the atomic scale things are much fuzzier than these diagrams suggest. Notice the difference between the cis and trans bonds - the four carbons in a cis bond are organized in a U-shape, whereas in a trans bond they are more like a Z.

Saturated and unsaturated fats

If the carbon backbone of the fatty acid is made entirely of single bonds it is called a saturated fatty acid - stearic acid shown below is an example of this.

If the backbone has one double bond the fatty acid is mono-unsaturated and if it has more than one it is poly-unsaturated. In the diagram below elaidic and oleic acids are examples of mono-unsaturated fats - you can see the double bond about half way along the chain, shown as two parallel lines joining the spheres. Notice how the cis bond in oleic acid gives it a kink, whereas stearic acid and elaidic acid are straighter. 

Polyunsaturated fatty acids

Before we move on from fatty acids we need to discuss the polyunsaturated variety. These are the ones that have more than one double bond. The position of the bond in the chain is important - you will notice in the diagram below that if you count the carbon atons (grey spheres) starting at the right hand end, the first double bond starts at position 3 for the top molecule and position 6 for the lower one. The top molecule is alpha-linoleic acid and it is found in soybean, rapeseed, flaxseed, and walnuts. Because of it's double bond in position 3 it is called an omega-3 fatty acid. The lower molecule, gamma-linoleic acid is an omega-6 type and is found in evening primrose oil.


Cells do not use fatty acids in their raw form. Two fatty acids are joined to a phosphate group to create a phospholipid molecule with very special properties. The phosphate end is attracted to water, whereas the fatty acid chains repel water. The resulting molecules have a tendency to form double layered membranes in water - the plasma membrane needed by cells.

In the example of a phospholipid shown below two different fatty acids have combined - a saturated type and a cis-monounsaturated type. This is important because it gives the plasma membrane the correct physical properties to function as a cell wall. If the fatty acids were all of the saturated type they could pack tightly together forming a rigid and inflexible structure. The kink caused by the cis bond of the lower fatty acid prevents this tight packing and allows the membrane to remain flexible.

Plasma membrane

So far I've described how carbon atoms form chains with their single and double bonds to form fatty acids, which are linked together by a phosphate group to form phospholipids. The diagram below shows how the phospholipids group together to form the double-layered plasma membrane. In this diagram I've simplified the carbon chains into zigzag lines and the phosphate groups into blue circles.

The left hand side of the diagram illustrates schematically a section of plasma membrane that is made up entirely of saturated or trans fats. Notice how the chains are able to pack tightly together, which makes them rigid and inflexible. On the right side is illustrated a section of plasma membrane containing 50% cis-unsaturated fats. The black chains are the saturated ones, and the red chains are shown as kinked, illustrating the effect of thge cis-double bond. The phospholipid molecules cannot pack together as tightly due to the kinkled cis-fatty acid chains - resulting in a membrane that is more flexible and biologically resilient.

Trans fats

This is the point at which the problem with trans fats starts to get clearer. If you look at the diagram of elaidic acid above you will see that it mimics a saturated fat, in that it is virtually straight, despite having a double bond. Trans fats are rare in nature, most food from natural sources contains very little of them, but fats that have been artificially hydrogenated or heated to high temperatures can contain them in significant amounts. Our bodies have not evolved to deal with these trans fats, they can't be broken down very easily, so they tend to accumulate in cell membranes. Here they affect the membrane properties, both physical and chemical, such as making them less flexible.

Because plasma membranes play such an important role in all aspects of our cellular functions, their disruption by trans fats can have consequences across multiple systems:

  • disruption of energy production in mitochondria, leading to fatigue
  • disruption of the immune system, which relies on membrane-bound receptors
  • disruption of hormone production, such as testosterone (infertility), insulin (diabetes)
  • loss of efficiency of liver cells, impairing detoxification
  • hardening cell walls, causing them to be more easily damaged and more permeable

As the links below show, trans fats are being linked to almost all chronic diseases, including heart disease, diabetes, cancer, obesity, osteoporosis, cognitive decline, and infertility, 

The next trap

The evidence against trans fats is accumulating, some countries have banned them outright, others are enforcing stricter labelling of products. However we need to be careful. Just eliminating trans fats will not ensure that the right kind of cis fats will be used instead. For thousands of years we have evolved eating food from purely natural sources, so the fats we consumed were those our bodies had evolved to handle. It appears that these are omega-3, omega-6 and omega-9, plus saturated fats. If trans fats are removed from the food chain, only to be replaced by other non-natural varieties, we may be no better off. Unfortunately it can take many years for the negative consequences of bad decisions to be revealed, by which time a whole generation can be affected.

The safest, and most resilient way is to rely as far as possible on unadulterated food, where minimal processing has taken place. Food that has been through any kind of manufacturing process should be viewed with caution.