A century ago scientists found that liquid oils could be converted to solid fats by a chemical process called hydrogenation.
What is hydrogenation?
As hydrogen was added to liquid oil it became a solid fat, which proved to be useful in food manufacture. Because of the addition of hydrogen, these new solid fats became known as hydrogenated vegetable oils, or HVOs.
What is partial hydrogenation?
Partial hydrogenation means that a product is partially hardened using the same process as hydrogenated oil but is softer and it has a lower melting point.
What are trans fats?
There are two main types of fat: saturated and unsaturated.
All fats are made up of chain-like molecules - animal fats have flexible chains which stay hard when cool (saturated) while vegetable oils are more rigid, which allows them to stay liquid at room temperature (unsaturated).
During hydrogenation of vegetable oil some parts of the rigid, unsaturated chain change shape and become less rigid trans fats - a type of saturated fat - which the body can't properly digest.
The amount of trans fats in HVOs varies depending upon the degree of hydrogenation. It can range from less than 1% for fully hydrogenated oils, to as much as 60% in partially hydrogenated oils.
Some trans fats are also found naturally in very low levels in foods such as butter, cheese, milk, beef and lamb.
Why are they used?
Vegetable oils are cheaper than animal fats and, during the 1950s, hydrogenation was widely adopted. Margarines were developed as alternatives to butter, and vegetable shortenings began to replace animal fats in cooking. Margarines no longer contain hydrogenated fats, though. Manufacturers use HVOs in their products because they are inexpensive and taste-free. They also keep the final product fresher for longer and improve its flavour and texture.
Why are hydrogenated fats controversial?
Although hydrogenated oils are very useful in food production, recent evidence has shown they have a harmful effect on the body.
High levels of cholesterol in the blood increase the risk of coronary heart disease. Research shows that trans fats, created by hydrogenation, raise levels of LDL cholesterol (also known as ‘bad' cholesterol). It's also thought that they decrease levels of HDL cholesterol (also known as ‘good' cholesterol). Certainly trans fats are at least as bad for your heart health as saturated fats, and some research suggests they are worse.
This highlights how important it is to control the amount of hydrogenated and partially hydrogenated oils that we eat. Since 1994, the Food Standards Agency has recommended that trans fats make up no more than 2% of the calories we eat each day. Currently in the UK we eat, on average, about half that amount.
However, we consume about 20% more saturated fat than the recommendations. With this in mind, we should concentrate on trying to reduce the amount of total fat and saturated fat that we eat. To reduce your sat fat intake, try cooking with sunflower, olive or rapeseed oil, instead of butter, lard or ghee; switch to skimmed or semi-skimmed milk; cut off visible fat from meat and only eat foods high in fat, like cakes and pastries, as an occasional treat.
How do I know if the food I buy contains trans fats?
Under European law manufacturers don't need to declare whether their products contain trans fats. However, hydrogenated oils do need to be declared in the ingredients list, so check for ‘hydrogenated' or ‘partially hydrogenated vegetable oils'. The higher up the list they are, the more the product contains. Although the amount of trans fats they contain can vary, it's best to avoid these foods altogether.
ASDA's own label products
There is no need to worry about hydrogenated vegetable oils when buying any of ASDA's own label foods or soft drinks products. When we removed artificial colourings and additives, we also removed hydrogenated and partially hydrogenated vegetable oils from all of our products. We know that our customers are concerned about what's in the food that they buy. By removing all the ingredients which we don't need from our own label food and soft drinks, we aim to make life easier and healthier for your and your family.