What are trans fats?
Trans fats are found mainly in deep-fried fast foods and processed foods made with margarine or shortening. They’re created by hydrogenation, a process that’s been used by the food industry for about 100 years, in which liquid oils rich in polyunsaturated fats are converted into more solid (and more saturated) fats suitable for making cakes and pastries.
Trans fats are also formed in the process of refining polyunsaturated oils, and some cooking oils used by fast-food outlets and bakeries for deep frying are also partially hydrogenated to slow the process of oxidation that can turn the oil rancid.
Advances in food technology, however, have made it possible for manufacturers to produce cooking oils, margarines and shortenings without depending so much on hydrogenation. There are now no valid technical reasons for manufacturers to continue using hydrogenated fats and oils.
Some foods, mainly beef, lamb and dairy products, contain naturally occurring trans fats. These fats are produced by micro-organisms in the rumen (or fore-stomach) of cattle and sheep, which partially hydrogenate the fats and oils from the animals’ feed. A recent survey found that on average about 60% of trans fats in the Australian diet come from these natural sources.
What are the risks?
Trans fats increase your risk of heart disease and sudden death from heart-related causes.
Like saturated fats, trans fats can raise total blood cholesterol levels, as well as the LDL, or “bad” component, of blood cholesterol. But they’re worse than saturated fats in that they can also lower the “good” HDL component. There’s also some evidence that these fats may increase your risk of developing diabetes.
Experts agree that, gram for gram, the risks from trans fats are greater than from saturated. In fact, the evidence against trans fats is so strong that
- Denmark and Switzerland have banned the sale of foods in which trans fat is more than 2% of the total fat content.
- In Australia, the National Heart Foundation Tick program limits trans fats to less than 0.2% of fat for all products except margarine-type spreads and vegetable oils which must limit trans fat to less than 1% of total fat.
- The World Health Organization (WHO) recommends trans fats contribute less than 1% of our daily energy intake – less than 2.3g of fat for someone with an average daily energy intake of 8700kJ – and some experts now recommend complete or near-complete avoidance of industrially produced trans fats to avoid adverse heath effects.
The risk from naturally produced trans fats compared with industrially produced ones is less clear. There are chemical differences between the two, and some recent research seems to suggest naturally occurring trans fats are not as harmful – but experts still disagree on the issue.