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Trans fats have been in the news recently, with trans fats being banned in New York City restaurants from 1 July 2007 and with growing vocal opposition to trans fats in the European Union.1
Trans fats occur naturally in meat and dairy products at a level of up to 10% of total fat. They are produced by bacterial activity in the guts of ruminants such as sheep and cattle.2 Previously this was the only source of trans fats consumed by humans until the process of partial hydrogenation of unsaturated fats was discovered in the early 1900s.3
Partial hydrogenation alters the structural chemistry of unsaturated fats and creates a fat that has a higher melting point, which is less prone to oxidation and hence lowers their rancidity, thus prolonging the shelf life of goods containing them (Figure 1).
Chemically, trans fats are made of the same carbons, hydrogens and oxygen molecules as non-trans fats, but they have a different shape. In trans fat molecules, the hydrogens on the double bonded carbon atoms (characteristic of all unsaturated fats) are in the trans configuration (hydrogens on opposite sides of the double bond) rather than the cis configuration (hydrogens on the same side as the double bond) configuration.
As a result, trans fats are less fluid and have a higher melting point than the corresponding cis fats.
The process of partial hydrogenation led to the development in the 1970s of margarines with a long shelf-life and a smooth spreadable texture.3 Trans fats are also found in shortenings, which are commonly used for deep frying in restaurants and in the fast food, snack food, fried food, and baked goods industries.
The partial hydrogenation of unsaturated fats was initially embraced by health professionals as the new fats substituted the atherogenic saturated fats already used in foods. However, it has since become apparent that trans fats are harmful, with an intake as low as 5 grams per day associated with a 25% increase in the incidence of cardiovascular disease over a 10-year history of exposure.4
Figure 1. Chemical structure of trans fatty acids (trans fats)
[Image omitted. See PDF]
Not only do trans fats increase low density lipoprotein (LDL), as do saturated fats, but they have the added harmful effect of reducing...