According to the Food and Drug Administration (FDA), trans fat is found in vegetable shortenings, some margarines, crackers, cookies, snack foods, and other foods made with or fried in partially hydrogenated oils. Unlike other fats, the majority of trans fat is formed when food manufacturers turn liquid oils into solid fats like shortening and hard margarine by adding hydrogen.

Trans fats are created when vegetable oil is heated to super-high temperatures and hydrogen is bubbled through, creating new chemical bonds with a similar structure to plastic. A hard fat is produced that has a high melting point and a long shelf life. Trans fats are therefore more economical.

Researchers at Wake Forest University Baptist Medical Center, who were examining the role of trans fats in atherosclerosis (clogged arteries) took two groups of 25 monkeys and, over six years, fed them on a diet containing the same number of calories.

One group received 8 per cent of their dietary fat in the form of mono-unsaturated fats, while the other received 8 per cent of their fat in the form of trans fats (trans fatty acids).

Professor Lawrence Rudel, head of the Lipid Sciences Research Program at Wake Forest University says they did not think the rats would get obese because they were not given enough calories and the team were surprised by the outcome.

It seems the monkeys fed trans fats had a 7.2 per cent weight gain, compared to 1.8 per cent in the group given mono-unsaturates and computed tomography images showed that the trans fat-eating monkeys deposited 30 per cent more fat in their abdomens.

Dr. Rudel says trans fat is worse than anticipated.

The researchers are confident that the same weight changes and fat redistribution would occur in humans fed on a high-trans fat diet.

The researchers say the six-year length of the study was equivalent to 20 years in people.

Denmark in 2004 made it law for manufacturers to label trans fats on all food labels and decreed that no item can contain more than two per cent of them.

FDA also made it law for manufacturers to list trans fats on nutrition labels early this year.

Currently accepted guidelines suggest that fat should make up no more than 33 per cent of our total calorie intake and of that, saturated fat should be no more than 10 per cent or less.

Polyunsaturated fats which are found in sunflower oil, soya oil and fish oil, are believed to lower bad cholesterol and Omega 3 and omega 6 fatty acids which are polyunsaturated fats and are considered a healthy fat.

Mono-unsaturated fat found in olive oil, nuts and avocados also lowers cholesterol and is also considered a healthy fat.

Trans unsaturated fatty acids (Trans fats) increase LDL (bad cholesterol) and decrease HDL (good cholesterol) and are thought to raise the risk of coronary heart disease ten-fold more than saturated fats.

Conjugated linoleic acid (CLA), are natural trans fatty acid found in dairy foods and meat and some studies suggest CLAs improve immune function and prevent narrowing of the arteries.