What is trans fat? | New Scientist

Trans fats are mainly found in processed food, like biscuits, cakes, and fried foods like crisps and chips, and to a lesser extent some natural foods such as meat and even breast-milk. The food we eat contains many different types of fats and oils – collectively known as lipids – and it used to be thought that the main distinction that mattered for our health was whether they are saturated or unsaturated. Saturated fats tend to be solid at room temperature and are mainly found in animal products such as meat and dairy. Unsaturated ones tend to be liquid and are found in plants.

For a long time, saturated fats were thought to be the worst for our health, as they raise blood cholesterol levels, contributing to heart attacks. This is why we are advised to replace saturated fats with unsaturated, such as eating margarine instead of butter, and cooking with vegetable oil instead of lard.

But there’s a problem. For decades manufacturers used a chemical process called hydrogenation to turn the liquid vegetable oils into solids, and that process creates trans fats. Multiple studies have found that trans fats are even worse for our hearts than eating saturated fats. Even though they are unsaturated, industrially produced trans fats seem to particularly raise levels of the most dangerous forms of blood cholesterol and promote low-level body-wide inflammation. So until recently, it would have been better to eat butter than the so-called “heart healthy” margarines.

But as our understanding of the effects of trans fats grew, firms started changing their food manufacturing processes and trans fats are now present in much lower levels. In the past few years most western countries have introduced legal limits on the trans fat content permitted in processed foods. Clare Wilson