Trans fats are chemically altered vegetable oils. They are produced artificially in a process called hydrogenation which turns liquid oil into solid fat.
Trans fats can be found in thousands of processed foods from sweets and biscuits to ready meals. They are used because they are cheap, add bulk to products, have a neutral flavour and give products a long shelf life. They have no nutritional value.
Are trans fats bad for you?
Trans fats have been linked to high cholesterol, which can lead to health conditions such as heart attacks and strokes.
A study suggests that trans fats can also increase the risk of fertility problems. Researchers from the Harvard School of Public Health in Boston, USA, say that consuming just 4g of trans fats every day can lead to infertility in women.
Avoiding trans fats
In the UK, there is no specific requirement for the trans fat content of products to be included on food labelling.