On November 17, 1999, the FDA published a proposed rule that would require the amount of trans fatty acids in a food, including dietary supplements, to be included in the amount and percentage Daily Value declared in the nutritional labeling of saturated fats . When trans fatty acids are present, the declaration of saturated fatty acids would be required to contain a symbol that refers to a footnote stating the number of grams of trans fatty acids per serving. Trans fatty acids would be subject to the same limits as saturated fats for the purposes of nutrient content claims, health claims, or disclosure and disqualifying levels. The FDA also proposed to define the nutrient content claim for “trans fat free.”
Dietary fats are composed of fatty acids and glycerol. Dietary fatty acids consist of carbon chains of various lengths and a terminal carboxyl group. The carbon atoms in these chains are connected by single or double bonds. Hydrogen atoms are attached to the noncarboxyl carbons.
A saturated fatty acid has no double bonds between the carbon atoms in the chain. An unsaturated fatty acid may contain one or more double bonds between carbon atoms and, therefore, two fewer hydrogen atoms per double bond. A fatty acid with a single double bond is called a monounsaturated fatty acid. A fatty acid with two or more double bonds is called a polyunsaturated fatty acid.
Most naturally-occurring dietary unsaturated fatty acids are in a cis configuration, i.e., the two hydrogen bonds attached to two carbons are on the same side of the molecule at the double bond which gives the molecule a “bend” at the site of the double bond . These bent molecules cannot pack easily together, so fats of these molecules are more often in a liquid form. In a trans configuration, the hydrogen atoms attached to the carbon atoms at a double bond are not on the same side of the double bond. (“Trans” means “across” in Latin.) This arrangement stabilizes the molecule in a relatively straight contour. The FDA is proposing to define trans fatty acids as “unsaturated fatty acids that contain one or more . . . double bonds in a trans configuration.”
Trans fatty acids are primarily the result of hydrogenation, a process by which hydrogen atoms are added to unsaturated sites on the carbon chains, thereby reducing the number of double bonds. In partial hydrogenation, some double bonds remain but may be moved in their positions on the carbon chain and changed from a cis to trans configuration. Hydrogenation increases the melting point, shelf life, and flavor stability of unsaturated fatty acids. Through hydrogenation, oils (fats in liquid form), such as soybean, safflower, and cottonseed oil, which are rich in unsaturated fatty acids, are converted to semi- solids and solids that are useful in margarines and vegetable shortenings. Hydrogenation also occurs in the digestive tract of ruminant animals, but the resultant trans fatty acids comprise only a small percentage of the total fatty acids of such products.
The partial hydrogenation process was developed in the 1930s and has been in widespread commercial use since the 1940’s. Dietary fats containing hydrogenated fatty acids, such as those used in margarine, have gradually displaced animal fats, such as butter and lard in the average American diet. About two-thirds of the dietary fat consumed in the 1940s was of animal origin. The balance was reversed by the 1960s, with two- thirds coming from fats of vegetable origin. This trend resulted in a decrease in the intake of saturated fat and an increase in the intake of polyunsaturated and trans fatty acids. The American Heart Association has recommended:
- Naturally occurring unhydrogenated oil should be used when possible.
- Attempts should be made to substitute unhydrogenated oil for hydrogenated or saturated fat in processed foods.
- Softer margarines should be substituted for harder margarines and cooking fats .
ASCN/AIN Labeling Recommendations
In 1996, a task force of the American Society for Clinical Nutrition/American Institute of Nutrition recommended:
- Trans fatty acids should be added to or included with saturated fatty acids on labels
- Trans fatty acids should be a separate class on labels
- There should be a threshold proportion of trans fatty acids for health claims/ This proportion (g/portion), if exceeded, will preclude use of a low- fat, low-saturated fat descriptor or health claim on the label.
- Fatty acids should be classified as cholesterol-raising and cholesterol-lowering 
The task force indicated that its proposal ignored differences in individual responsiveness to each fatty acid as well as their possible effects on risk factors in chronic diseases other than cardiovascular ones. The FDA’s proposed rule noted that more recent studies have strengthened the link between trans fatty acids and coronary heart disease (CHD).
Based on its analysis of scientific reports, the FDA has concluded:
- Consuming trans fatty acids (rather than cis-monounsaturated or polyunsaturated fat) can raise the level of low-density lipoproteins (LDL), which is a major risk factor for CHD.
- Although interventional studies are too short in duration to provide direct evidence on the incidence of CHD, they provide evidence for an effect of dietary trans fatty acids on LDL.
- Epidemiologic studies have consistently found associations between estimated dietary intake of trans fatty acids and the incidence of CHD.
- The available studies do not provide a definitive answer to the question of whether trans fatty acids have an effect on LDL and CHD risk equivalent to saturated fats on a gram-for-gram basis. They also do not provide information about mechanisms responsible for the observed increases in LDL However, the repeated and consistent findings under a variety of conditions are strong evidence of a relationship between consumption of higher levels of trans fatty acids and increased risk of CHD .