What are hydrogenated fats and trans fats?
Hydrogenation is the process that turns liquid oil into a more solid fat. Liquid oils are ‘hardened’ by adding hydrogen to stabilise the fat, making it easier to use in recipes for biscuits, cakes, pastry, and other processed foods.
You can tell how ‘saturated’ a fat is by its texture at room temperature. Saturated fats like lard, fat on meat and cheese are solid at room temperature, whereas unsaturated fats - such as vegetable oils - are liquid at room temperature. As an unsaturated oil is gradually more hydrogenated, the inserted hydrogen atoms make it firmer and more solid at room temperature.
Usually, the hydrogen slips naturally into the fat at the point where there is a gap (called an ‘unsaturated bond’) in the fat structure. The position it takes up is called the ‘cis’ position, which occurs naturally in nature as well.
Sometimes the hydrogen slips into the gap in a different position, altering the overall shape of the final fat. The ‘trans’ position of the inserted hydrogen alters the overall shape of the fat, making it difficult for our body to process. Foods containing hydrogenated vegetable oil (always declared in the ingredients list) may therefore also contain trans fats.
Trans fats found in food have no known nutritional benefit and appear to be harmful. They increase blood cholesterol levels and independently increase the risk of heart disease. Some evidence suggests that the effects of these trans fats may be worse than saturated fats.
So, as part of a healthy diet we should try to reduce the amount of foods we eat that contain hydrogenated or saturated fats and replace them with unsaturated fats. And it's also important to reduce the total amount of fat we eat.
Biscuits, cakes, pastries, meat pies, sausages, fast foods and foods containing coconut or palm oil all tend to be high in saturated fats, so try not to eat too much of these.
Foods that are rich in unsaturated fats include oily fish, avocados, nuts and sunflower, rapeseed and olive oils.
Trans fats are also naturally found at very low levels in foods such as dairy products, beef and lamb. However, the type of trans fat found in dairy products (such as milk, cheese and cream) is different to other types of trans fat and are not considered harmful to health.
Why we should follow a low-fat diet?
Fat is the most energy-dense nutrient, providing 9kcal per gram, so high fat foods tend to be those higher in calories than lower fat alternatives. If you’re trying to keep your weight in check it’s a good idea to reduce overall fat intake.
A common mistake is to think that oils provide less calories than margarine due to being liquid. This is a myth - two teaspoons of any type of oil provides around 90kcals - the same as a slice of bread.