Trans fats—fatty acids having at lease one double bond in the trans configuration—form during partial hydrogenation of vegetable oils that is intended to convert them into semisolid fats to be used in commercial cooking. These products have a long shelf life, are stable during deep frying, and are semisolids that are conveniently used in baked goods and sweets. Consumption of industrially produced trans fatty acids in the United States is estimated at 2% to 3% of all calories consumed. Major sources include, in addition to deep-fried fast foods and bakery products, packaged snack foods, margarines, and crackers. Approximately 0.5% of total energy intake consists of naturally occurring trans fats found in meats and dairy products from ruminants such as cows and sheep. The U.S. Food and Drug Administration now requires that labels for all conventional foods and supplements include their content of trans fatty acids.
Analysis of 12 randomized trials totaling more than 500 subjects showed that, compared with equal calories from saturated or cis unsaturated fats, consuming trans fatty acids increases low-density lipoprotein cholesterol, lowers levels of high-density lipoprotein (HDL) cholesterol, and increases the ratio of total to HDL cholesterol, blood triglyceride levels, and levels of Lp(a) lipoprotein. There is evidence that trans fats promote inflammation through increases in tumor necrosis factor α, interleukin-6, and C-reactive protein. Trans fats may, in addition, cause endothelial dysfunction.
On a per-calorie basis, trans fats reportedly increase the risk of coronary heart disease (CHD) more than any other macronutrient. The risk is substantially increased when consumption is only 1% to 3% of total energy intake. In an analysis of 4 prospective cohort studies totaling nearly 140,000 subjects, a 2% increase in energy intake from trans fatty acids was associated with a 23% increase in the incidence of CHD (pooled relative risk, 1.23; 95% confidence interval, 1.11–1.37). Some results suggest that trans fatty acids may increase the risk of sudden cardiac death.
To avoid adverse effects of trans fat, it may be necessary to avoid, or nearly avoid, consuming industrial products so that trans fat will constitute less than 0.5% of total energy intake. Physicians and other health career providers can inform their patients about how to avoid the worst offenders, and they also can support institutional efforts to reduce the use of trans fat in food services at schools, hospitals, and other worksites. Food manufacturers and restaurants may seek alternatives to partially hydrogenated oils. The authors estimate that reducing the consumption of trans fat in the United States might prevent 10% to 19% of CHD events.