Chewing the fat on trans fats

Background and epidemiology: Trans fatty acids, or trans fats, are unsaturated fats produced through partial hydrogenation, when vegetable oils are heated in the presence of metal catalysts and hydrogen.1 Hydrogenation increases the shelf life and stability of fatty acids and foods containing them. During partial hydrogenation, some double bonds between carbon atoms remain but may shift to a different position along a chain and alter their configuration from cis to trans fats.

Figure. Photo by: Photos.com

Trans fats are present in many food products, including vegetable shortening, margarines, baked goods, snack foods, fried foods, salad dressings and many processed foods. Low levels are also found in dairy products, lamb and beef fat, because small amounts of trans fat are produced in the gastrointestinal tract of ruminants.

As much as 22% of the average intake of trans fats by Canadian adults is provided by foods consumed away from home.2 The intake of trans fats has been shown to increase the risk of heart disease by raising low-density lipoprotein (LDL) cholesterol levels and lowering high-density lipoprotein (HDL) cholesterol levels. This combined effect on LDL and HDL cholesterols is double that of saturated fatty acids.3 The effect on triglyceride and Lp(a) lipoprotein levels is also greater than that of saturated fats; high blood levels of Lp(a) lipoprotein have been independently linked with an increased risk of coronary artery disease (CAD). Trans fats may also have other adverse effects on thrombogenesis through altered prostaglandin balance.4 Results of large cohort studies have shown increased relative risks for CAD with high trans fat intake (Table 1). There have been no safe limits of trans fat consumption shown.

Prevention: Some countries have effectively imposed a ban on trans fats (e.g., Denmark has banned oils and fats that contain more than 2% trans fats). In Canada, Health Canada and the Heart and Stroke Foundation of Canada have formed a task force to address trans fat consumption that will target public education, food labelling and ways for the food service and food-processing industries to reduce the use of trans fats. In addition, guidelines are being developed for the provision of nutrition information by chain restaurants to customers, and restaurants are requested to use modified recipes and ingredients containing lower amounts of trans fats.

International harmonization of nutrition labelling regulations is also being addressed. Companies importing food products do not currently have to follow the same labelling regulations as manufacturers of food products in Canada. For example, a “trans-free” product in Canada must contain less than 0.2 g of trans fat per serving and must also be low in saturated fats; in the United States, the limit of trans fats is 0.5 g. Compliance with nutrition labelling regulations by most food manufacturers in Canada and companies wishing to import food products is required by Dec. 12, 2005; small companies will have until Dec. 12, 2007, because of reduced capacity to meet the regulations.

Product labelling of trans fat content is expected to make a difference: the regulation issued in 2003 by the US Food and Drug Administration requiring that manufacturers list trans fats on the labels of food products and some dietary supplements is expected to prevent 600 to 1200 cases of CAD and 250 to 500 CAD-related deaths each year.5

Practice implications: There have been no safe levels of trans fat consumption shown, and dietary trans fat and saturated fat intake should be reduced. Consumers should take advantage of the new labelling regulations and select products that contain low levels of trans and saturated fats.