New Studies Add to These Fats' Image Problem. (Trans Fats)

Article excerpt

Supermarkets are stocked with enough varieties of butter, margarine, and spreads to give a shopper pause. It's no small task to decipher which sticks and tubs contain which types of fat--and which fats are best for your health.

The skinny on fat keeps changing. Whereas nutritionists first differentiated between just a couple types of fats, a subcategory of the forms that seemed less harmful later came to be seen as risky, after all (SN: 5/21/94, p. 325). Over the past several years, evidence has continued to mount against the food component called trans fat. It's been implicated in diseases ranging from coronary heart disease to diabetes.

Trans fats are almost everywhere in the U.S. diet. They transform vegetable oils into solid substances suitable for use in many foods. From french fries and margarine to store-bought cookies and crackers, trans fats are ubiquitous in fast food restaurants and grocery stores. Consumers don't yet see these fats listed in the "Nutrition Facts" box on a tub of margarine, but they already can find dairy-aisle spreads advertised as being low in trans fat.

Now, while some researchers are conducting new studies to further investigate the role of trans fats in disease, others are learning how to make appealing foods with fewer trans fats. To be sure, both the basic and applied sciences of trans fats have become hot.

Categories of fats get their names from their patterns of hydrogen atoms in the molecules. All fatty acids, which make up fats, contain chains of carbon atoms with hydrogen atoms attached to some or all of the carbons.

Unsaturated fats, such as those in corn and soybean oil, have double bonds at a variety of positions along their carbon chains. Typically, each carbon atom participating in a double bond also bonds to one hydrogen atom and the next carbon atom in the chain. Fats with one double bond are called monounsaturated, and those with more double bonds are polyunsaturated.

Saturated fats, such as those found in butter, get their name because they don't have any double bonds--the carbon chain holds the greatest possible number of hydrogen atoms. Earlier research linked saturated fats to a variety of diseases, so many people switched to products, like margarine, that contain unsaturated fats.

Trans fats contain a type of unsaturated fatty acid that didn't raise much of a health alarm until the past decade. Their name refers to a feature of their bonds. At the location of each double bond, a fatty molecule bends, either in a so-called cis or trans direction. Cis configurations are those in which the molecule on both sides of the double bond bends in the same direction--both either up or down. In trans configurations, the chain bends in opposite directions on either side of the double bond--making a zigzag.

There are some naturally occurring trans fats, primarily in the meat of cows and other ruminant animals. But most trans fats in foods come from the processing of oils for margarines, shortenings, and prepared foods.

To transform vegetable oils into solid or semi-solid substances, producers change some double bonds into single bonds. The most common process that they use is called partial hydrogenation. This method leaves many fatty acids in the trans formation, which assemble, like a stack of chaise lounges, into a solid much easier than those in the cis shape do.

As of yet, there isn't a consensus among health professionals about how a diet high in trans fats compares to one heavy in other fats. However, the most recent research is adding to the already worrisome case against trans fats. The fats first raised concerns because studies in 1990 suggested that they raise concentrations of the so-called bad form of cholesterol, or LDL, in the body while lowering levels of HDL, the good form of cholesterol. What's more, other research since then has linked diets containing a lot of trans fat to coronary heart disease. …