Hydrogenated Fats

The process of hydrogenation of fats and oils, was adopted in the early part of the 20th century as a way to both extend the shelf life of fats and oils, and to make more spreadable margarines. Fats and oils are one and the same, with oil being used to refer to fats that are liquid at room temperature and fats referring to fats that are soild at room temperature. If a fat (solid at room temperature) is used to make crumbly pastry, it is known as a shortening. In the past the main shortening was lard (pig fat).

Just what is fat?

Before describing hydrogenated fat it is worthwhile being clear about what fat is. Fat in our body and in our food comes in the form of triglycerides. Basically three fatty acids attached to a glycerol backbone. A lot of the discussion about good and bad fats relates to the nature of these fatty acids (saturated, monounsaturated, polyunsaturated etc.). It is worth remembering that the basic fat molecule in your body or in the foods that you eat is a triglyceride and can contain both good and bad fatty acids. So it is quite possible to consume saturated, monounsaturated and polyunsaturated fat in just one fat molecule.

In practice most foods contain a percentage of each type of fat. Some are very high in one and very low in another. An example is meat in which monounsaturated and saturated fat predominate. In oily fish, polyunsaturated fat and monounsaturated fat predominate. When we look at hydrogenation below we are considering what happens to just one of the fatty acids in a normal fat (triglyceride). In most cases there are two fatty acids on each triglyceride that are easier to change than the other one.

Hydrogenated fats - what are they?

The term hydrogenated fat is applicable to any fat or oil that has been treated by the process of hydrogentaion. In this process fats are heated along with a catalyst, normally nickel, that enables the fat to combine with hydrogen atoms. Not all fats can combine with hydrogen. Those that are saturated have as many hydrogen atoms as it is possible to have, that is why they are known as saturated fats. On the other hand unsaturated fats have space for more hydrogen atoms.

Looking at the diagram to the left there are carbon (C) atoms that form the backbone of all fatty acids. Carbon has four free arms to connect with other atoms, while hydrogen has just one. In the unsaturated fatty acid you can see in green two carbon atoms in a double bond. Their shared arms can be released by the process of hydrogenation, and attached to extra hydrogen atoms, making them look like the saturated fatty acid above them.

A fatty acid with one double bond is known as a monounsaturated fatty acid. Olive oil and most meat contains plenty of this type of fat. There are others known as polyunsaturated fats, including the omega 3 and omega 6 fats, that have more than one double bond. Oily fish, nuts and seeds and the oils derived from them contain plenty of these. When these unsaturated fats are hydrogenated, some of them become relatively benign saturated fats. However, the hydrogenation process is not perfect and many other types of chemical are normally produced. Hydrocarbon fragments and altered fatty acid products being two that are normally present. These are produced even if the hydrogenation process is run to completion, when all fatty acids have had their double bonds removed.

Hydrogenation - the unhealthy consequences.

On many occasions the hydrogenation process is not run to completion and the result is partial hydrogenation, which is a disaster for human health. In partial hydrogenation there are various other end products including:

  • Aldehydes
  • Double bond shifted fatty acids
  • Trans fats

The biggest problem seems to be the trans fats. This is not neccessarily because they are the most toxic, but because they are produced in large numbers. In a trans fat the hydrogenation process has not added a hydrogen atom in as intended, but has flipped the position of one of the carbon-hydrogen bonds so that it is on the other side of the fatty acid molecule, as shown to the right. This has the effect of straightening the molecule out. This sort of altered trans fat is not well recognised by our body and that is the reason it is associated with many negative health effects such as increased risk of cardiovascular disease and other inflammatory diseases such as osteoarthritis. A normal cis fat before it is transformed into the trans fat is shown below it.

How do I avoid these unhealthy fats?

The best advice is to eat whole foods and avoid packaged foods. Shopping locally and minimising what you buy from supermarkets may be difficult, but it will reduce the chances you end up buying products containing hydrogenated fats. Fruit, vegetables, nuts, meat, fish and dairy produce all contain no hydrogenated products in their natural state. Lets look at a few types of food shop in turn.

  • Greengrocers - you will be hard pressed to find hydrogenated products in a greengrocers.
  • Butchers may contain some in breadcrumb toppings, but generally will have very few hydrogenated products.
  • A bakery will typically contain a fair amount of hydrogenated products. The breads are normally ok, but many pastries contain hydrogenated oils. Look for products produced with butter which will be OK.
  • Supermarkets are generally worse than local shops as they have to keep products on the shelves for longer. Looking at the labels on packaged products gives a clue as to whether they contain hydrogenated fats. Look for the word vegetable fat, vegetable oil, sunflower oil, safflower oil. If these appear you are likely to be in for a dose of trans fats. Breakfast cereals, bakery products, snack bars, ready meals and many sauces are all full of trans fats.
  • Motorway services and garages are generally what I'd term food deserts. There is very little healthy food available. The chocolate bars and crips that adorn most aisles are full of hydrogenated fats.

Haven't they banned these trans fats?

No, in the UK and most states in the US trans fats and the hydrogenation that produces them are not banned. In the UK the Food Standards Agency are alarmingly sanguine about the consequences of trans fats in the diet2. Their position appears to be that it is OK for trans fats to comprise up to 2% of our total food intake, and they are more concerned about the saturated fat that makes up 13% of our dietary intake. They ignore the fact that saturated fat intakes at this level are not linked with increased death rates at all3.

Trans fats are banned in some countries such as Denmark. They are also being phased out of own label products by some supermarkets4,5, however as always with these things you should not believe everything you hear from large food retailers. To claim that a food is trans fat free you only need to ensure that trans fats make up a certan portion of it, and bear in mind, no supermarket is free of hydrogenated oils, even if they have changed their own brand labels.

What about inter-esterified fats?

Yes, you guessed it, the food industry has come up with an alternative to hydrogenation. This process is based on swapping fatty acids around between the 3 arms on the glycerol molecule that holds a triglyceride together. In theory the fatty acids are not changed at all, and there should be no altered fatty acid products produced. However it seems that this process is not without its problems. A 2007 study comparing saturated fat with both partially hydrogenated and interesterified fats indicated that the effect of trans and interesterified fats on insulin and blood fat levels was of concern. These changes in the blood could easily lead to increased rates of diabetes and heart disease. What mechanism is responsible with inter-esterified fats is not yet clear, but it is yet another sign that manufactured food is almost invariably bad for your health.

The underlying reason that manufactured food is not good for us is, I suspect, that when we humans tinker with natural foodstuffs we create new compounds that have not ever been experienced by the human body. Basically our bodies have not yet evolved to cope with these new substances. Think what happens when you try something out for the first time. Have you ever seen somebody swim like a fish who has never swum before? Normally there are problems when something is encountered for the first time and this is certainly the case with most novel food chemicals.

DrDobbin says:

Avoid over processed foods. Those that contain fats that have been processed are likely to damage your health in the long term and for some people will affect their current state of health.


1) Fats that Heal, Fats that Kill, Udo Erasmus, ISBN 0-920470-38-6

2) http://www.food.gov.uk/scotland/scotnut/satfatenergy/transfat

3) http://www.ncbi.nlm.nih.gov/pubmed/21735388

4) http://www.waitrose.presscentre.com/content/Detail.aspx?ReleaseID=1583&N...

5) http://www.j-sainsbury.co.uk/extras/faqs/responsibility/food-and-health/...