One hundred years ago a newly patented process for hardening liquid fats by partial or full hydrogenation revolutionized food technology. Animal fats that people used for cooking and baking tended to spoil and produce off-flavors. Hydrogenation allowed the development of shelf-stable vegetable-based fats with neutral flavor. Vegetable shortenings and margarines eventually became household items because of wartime rationing of scarce animal fats. The versatility of the hydrogenation process promoted the industrial development of fats to achieve specific physical and chemical characteristics in processed foods.

Hydrogenated fats received another boost when scientific evidence related saturated fatty acid (saturated fat) intake to elevated low-density lipoprotein (LDL) cholesterol levels and risk for coronary heart disease. Health professionals advised people to reduce their intake of animal fats and choose products made with vegetable fats. With the realization that coconut, palm kernel, and palm oils contain a relatively high amount of saturated fat compared to other vegetable oils, dietary advice specified avoiding products containing these "tropical oils." In response, manufacturers replaced tropical oils with partially hydrogenated oils to maintain desirable freshness and texture in products such as French fries and baked goods. Although products made with partially hydrogenated oils are lower in saturated fat they also contain trans fatty acids (trans fat). Trans fats are produced during hydrogenation, with the amount depending on the degree of hydrogenation. Although trans fats are chemically unsaturated, they have functional properties similar to those of saturated fats.

Hydrogenated fats came into question when research during the 1990s indicated that increasing trans fat intake raises LDL cholesterol levels and possibly reduces high-density lipoprotein (HDL) cholesterol levels, thereby increasing the total cholesterol to HDL-cholesterol ratio. To address this public health concern, the Food and Drug Administration (FDA) proposed mandatory labeling of trans fat contents in 1999 and published a final rule in July 2003. Manufacturers have until January 1, 2006 to list the trans fat content on food labels. However, the trans fat-phobia that has developed during recent years has already prompted many manufacturers to disclose whether their products contain no declarable amount of trans fat (< 0.5 grams per serving) and others to reformulate products to eliminate or lower the trans fat content. Expect more food labels to declare the trans fat content well before 2006.

One unresolved issue is the lack of a Daily Value (DV) for trans fat. The DV is used to calculate a percent DV. Establishing a percent DV would help put a product's trans fat content in perspective on the food label by indicating to consumers how much trans fat is present compared with a daily amount. While the Food and Nutrition Board's Committee on Use of Dietary Reference Intakes in Nutrition Labeling recommended that saturated and trans fat content of foods use a combined DV, no scientific entity has recommended an amount of trans fat that FDA could use to establish a DV. A DV also would provide FDA with a basis for developing criteria and disclosure or disqualifying levels for nutrient content and health claims. Generally a 5 percent DV or less is "low" and a 20 percent DV or more is "high."

The 2002 Institute of Medicine (IOM) Dietary Reference Intakes Macronutrient Report did not provide quantitative dietary guidance for trans fat, saturated fat or cholesterol. Instead the IOM recommended that the intake of trans fat, saturated fat and cholesterol be as low as possible while consuming a nutritionally adequate diet.

The IOM recommendation has raised several questions. Can the available scientific evidence relating trans fat intakes and LDL cholesterol levels be re-evaluated in order to establish a DV? Should the current DVs for saturated fat (20 g) and cholesterol (300 mg) be reconsidered or revoked to provide a consistent labeling rationale? If there is no DV, what is the best way to put the trans fat (or saturated fat or cholesterol) content of a food into perspective?

In the absence of trans fat quantification on the food label health professionals and media have been instructing consumers to consult the ingredient list of each food product for "hydrogenated or partially hydrogenated" oils to detect the presence of trans fat. This practice is tricky at best and does not serve as a foolproof way to determine the presence or amount of trans fat in a particular product (see sidebar). When trans fat content is labeled, the FDA and health organizations are advising consumers to select products that have a lower amount of trans fat and saturated fat combined—a concept that may be difficult to communicate to consumers. It is apparent that we have not reached the end of the road to trans fat labeling.

What to Know about Trans Fat in Foods

Some products have already listed the amount of trans fat on the Nutrition Facts Panel. All others will do so before January 1, 2006. Since the presence of "hydrogenated" or "partially hydrogenated" oils does not serve as the best determinant of the trans fat content in foods, here are some facts to consider:

• Some margarines contain some partially hydrogenated oils, but the combined amounts of trans and saturated fats are often less than the amount of saturated fat in butter.
• Spreads with plant stanol or sterol esters also contain partially hydrogenated oils. The plant stanol/sterol esters provide a LDL-cholesterol labeling benefit and trans fat content is a negligible 0.5-1 gram per tablespoon.
• Peanut butters, which are rich in mostly beneficial unsaturated fat, may contain 1 to 2 percent partially hydrogenated oil to prevent oil separation. The resulting amount of trans fat is not detectable in a 2-tablespoon serving.