Trans fatty acids, commonly referred to as trans fats, are formed when vegetable oils are "hydrogenated" to harden and stabilize them. They have been associated with an increased risk of heart disease. The full extent of their impact on our health is not yet fully known. It is clear, however, that they raise blood cholesterol, although not as strongly as the saturated fats found in meats and dairy products. Researchers are now investigating other possible adverse effects.

Some researchers believe that too much trans fats may increase cancer risk. But results are difficult to interpret as studies find, for example, increased colon cancer in some people but not in others, or with some sources of trans fats but not all. Other researchers question whether increased trans fats during pregnancy could create imbalances that disrupt development of the nervous system in the fetus. Again, studies haven't established whether such problems actually occur.

For many people, the concern over trans fats has turned into a question of margarine versus butter. Actually, the soft margarine sold in tubs contains very little trans fats; it's only the harder stick margarine that is probably best avoided. Although it doesn't contain trans fats, butter is loaded with saturated fats, which are far more cholesterol-elevating.

For most Americans, other foods are more significant sources of trans fats. A recent report in the Journal of the American Dietetic Association notes that trans fats make up 25 percent or more of the fat in Danish pastries, doughnuts, cake mixes and certain types of popcorn and crackers. Studies generally find that after commercially-baked goods, the next major contributors are deep-fried and breaded fast foods.

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Because of the effects on blood cholesterol, the government's Dietary Guidelines recommend limiting consumption of trans fats. Unfortunately, many consumers are not well-informed about which foods contain them, and food labels do not list their content. But translating what we know about trans fats to food labels, in a way that's both accurate and understandable, is easier said than done.

More than two years ago, the Food and Drug Administration proposed a rule requiring the content of trans fats to be listed on the Nutrition Facts label of food products. The proposal was widely discussed by groups representing the food industry, consumers and nutrition professionals, but it is still not finalized.

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Part of the delay seems to be due to the difficulty of listing this information accurately yet clearly enough for consumers to understand. The initial proposal was to list one combined figure for saturated fats and trans-fats, since both raise cholesterol. But many nutrition professionals discouraged this as over-simplified. They note that further research may identify distinctions between the two fats that could have important health consequences.

For now, consumers should check the list of ingredients on snack foods and baked goods. If hydrogenated oil appears far down the list, there is no cause for alarm, but if it's near the top, a different product would probably be a better choice.

Some day, the confusion over trans fats will be cleared up but, in the meantime, you don't have to wait for more detailed nutrition labels to make smart choices for a healthier life. Avoid French fries and other deep-fried foods. Load up on veggies (but not deep-fried ones) and you won't have to worry about what type of fat is used. Nibble on low-fat, high-fiber cereal or fruit instead of pastries.

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