by Dariush Mozaffarian - Trans fats are unsaturated fatty acids with at least one double bond in the trans configuration. While small amounts of trans fats are naturally present in meats and dairy products from cows, sheep, and other ruminants, the great majority of trans fats in our diet are industrially-produced, contained in foods made with partially hydrogenated vegetable oils. Partial hydrogenation, which converts vegetable oils into semi-solid fats for use in margarines, commercial cooking, and manufacturing processes, converts approximately 30% of the natural fats to trans fats. In the US, consumption of trans fats averages between 2-4% of total energy, with major sources being deep fried fast foods, bakery products (cakes, cookies, muffins, pies, etc.), packaged snack foods, margarines, and breads.
Considerable evidence exists for harmful effects of trans fat intake. Furthermore, trans fats from partially hydrogenated oils have no intrinsic health value. Thus, little justification can be made for the use of partially hydrogenated oils, compared with other natural oils or fats. Importantly, adverse effects are seen at very low intakes: for example, 1-3% of total energy, or approximately 2-7 grams (20-60 calories) for a person consuming 2000 calories/day. Thus, complete or near-complete avoidance of industrial trans fats (≤0.5% of energy) may be necessary to avoid adverse effects and minimize health risks.
In 2004, Denmark became the first country to legislate limits on trans fat content of foods, largely eliminating industrial trans fats from all foods (including restaurants) in that country. Canada is considering similar legislation, and the city of Chicago is also considering banning industrial trans fats from restaurants. If restaurants and food manufacturers will not voluntarily eliminate trans fats (as has largely been done in the Netherlands), several points validate the need for, and the importance, of legislative measures to reduce the consumption of trans fats:
1. The harmful health effects of trans fats are now better established than for nearly any other substance in our food supply. The strength of evidence and the potential magnitude of harm greatly exceed those of food contaminants or pesticide residues, which are appropriately regulated to very low levels.
2. Extremely low levels of trans fat intake are associated with significantly increased risk of heart disease. In our analysis of prospective studies totaling 140,000 men and women, we determined that intake of 2% of total calories from trans fats (or 40 calories/day, for a typical 2000 calorie/day diet) was associated with 23% higher risk of heart attacks or death from heart disease. This indicates that for every 100,000 individuals suffering a heart attack or death from heart disease each year, 19,000 of these would be prevented if the average trans fat intake were reduced by approximately 40 calories/day.
3. Individuals have no means of evaluating the trans fat content of meals in restaurants. In contrast to packaged foods which now have standardized labeling of trans fat content, it is impossible for an individual to determine how much trans fat is present in restaurant meals. Mandated standardized labeling of all restaurant meals would be neither practical nor cost-efficient, given the ever-changing menus and diverse mixtures of ingredients of meals served in restaurants.
4. Use of trans fats in food manufacturing and restaurants can be limited without any significant effects on food taste, cost, or availability. While industry often expresses concern that limiting the use of trans fats will affect food taste or cost, no evidence exists to support this hypothesis. Conversely, substantial evidence exists that use of trans fats can be eliminated almost entirely without any effects on food taste, cost, or availability. This has been clearly demonstrated in both Denmark and the Netherlands.
It should also be emphasized that much less is known about trans fat consumption in developing countries. The current evidence suggests that, compared with Western nations, the intake of trans fats from partially hydrogenated oils may be much higher in developing countries, typically because partially hydrogenated oils represent the cheapest (and often subsidized) choice of fat for cooking. Given that coronary heart disease is the leading cause of death in nearly all countries, including developing nations, intensive efforts must be undertaken to greatly reduce or eliminate use of partially hydrogenated oils in both the developed and the developing world.
In summary, considerable evidence exists for harm, and little evidence for intrinsic health value, of consumption of trans fats from partially hydrogenated vegetable oils. Elimination of industrial trans fats from foods, either by voluntary or legislative measures, would likely prevent tens of thousands of heart attacks each year in the U.S. and other countries.

Dariush Mozaffarian, is a professor at Harvard Medical School and Harvard School of Public Health.

Copyright: Project Syndicate, 2006.
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