Trans fat is a type of
fatty acid found in processed foods that has been shown by several studies to raise the levels of
LDL-C ("bad"
cholesterol) in the blood, to a degree comparable to saturated fats. Elevated levels of LDL-C increases the risk of developing
Coronary Heart Disease. Trans fat is sometimes glibly referred to as "stealth fat," because for many years it was not labeled on food packaging.
What are trans fats?
There are three main types of fatty acids: saturated fat, unsaturated fat. and trans fat. Fatty acids are chains of carbon atoms with hydrogen atoms attached to the carbon atoms. A saturated fatty acid has the maximum possible number of hydrogen atoms attached to each carbon atom, like so:
H H
| |
-C-C-
| |
H H
In an unsaturated fatty acid, one or more pairs of hydrogen atoms in the middle of a chain are missing, creating gaps that leave two carbon atoms connected by a
double bond rather than a single bond:
H H
| |
-C=C-
Trans fats are a third type of fatty acid that generally does not occur naturally. Most trans fats are found in "partially-hydrogenated" vegetable oils.
Hydrogenation is a process whereby hydrogen is bubbled through
oil to produce
margarines that don't melt at room temperature, thus increasing a product's shelf life. Whereas in normal fats the hydrogen atoms at a double bond are positioned on the same side of the carbon chain, hydrogenation reconfigures some double bonds such that hydrogen atoms end up on different sides of the chain:
H
|
-C=C-
|
H
This type of configuration is called "trans" from the
Latin for "across."
Where are trans fats found?
Partially hydrogenated vegetable oils, which contain trans fats, are present in about 40 percent of the food on grocery store shelves. Cookies, crackers, and microwave popcorn are the biggest sources of trans fats, which are also found in other processed foods such as margarine1, salad dressings, cakes, donuts, snack chips, chocolate candy, processed breakfast cereals, french fries, and many cooking oils.
Even foods labeled "low in cholesterol" or "low in saturated fats" may have high percentages of trans fats. The FDA has recently proposed that trans fat be listed along with saturated and unsaturated fat in the "Nutrition Facts" section of food packaging, but has met stiff resistence from snack food companies and their allies in Congress.
Because trans fat is not labeled, it is very difficult for consumers to accurately judge the relative healthiness of food products. For example, product A might be labled as having 3g of saturated fat, while product B has 4g of saturated fat. A seems healthier, right? But product A could have 4g of unlabled trans fat, while product B might have no trans fat, meaning that product A has 7g of "bad" fat while B only has 4g.
What are the health risks associated with consumption of trans fats?
Trans fats, which very rarely occur naturally in unprocessed food sources, have no known nutritional benefits. The sole utility of trans fats is to increase product shelf lifes by retaining flavor and texture, through the technique of partial hydrogenation. When trans fats were first recognized in the 1980s, early studies found no effect, either negative or positive from the consumption of trans fats, other than those already associated with the consumption of other fats.
In the early 1990s however, researchers began to look for the first time at the relationship between trans fat intake and LDL-C levels. Based on the newer research, a National Cholesterol Education Program publication in 1993 entitled "Second Report of the Expert Panel on Detection, Evaluation and Treatment of High Blood Cholesterol in Adults," found that trans fatty acids raise LDL-C levels nearly as much as similar amounts of saturated fats, despite their presence in foods low or lacking in saturated fat. Further research has overwhelmingly corroborated these findings.
The FDA estimates based on consumer research that merely informing customers for three years about trans fats on food labels could prevent 6,300 to 12,800 cases of coronary heart disease and 2,100 to 4,200 deaths per year. The FDA further estimates that a reformulation of margarines and baked products to eliminate trans fats, while costing the food industry roughly $1 billion, could save the nation nearly $60 billion in health-care costs.
1. Many people assume that butter is more "natural" than margarine and therefore must be healthier. While margarine may contain more trans fat than butter, the total of trans and saturated fat (the LDL-C raising fats) in margarine is always less than the total saturated fat in butter. Thus both the FDA and the U.S. Department of Agriculture recommend margarine over butter and suggest that nonstick cooking spray may be substituted for other fats when greasing pans. Since these recommendations were released in a 1995 report from the U.S. Department of Agriculture based on Department and FDA data, the margarine industry has reformulated many of its products to reduce saturated and trans fat content, making margarine even healthier in comparison to butter (although still plenty unhealthy).
Sources:
- Associated Press. "Suit Seeks to Ban Kids From Eating Oreos." http://story.news.yahoo.com/news?tmpl=story&u=/ap/20030512/ap_on_fe_st/oreo_suit_1
- ConsumerReports.org "Trans fat." http://www.consumerreports.org/main/detailv2.jsp?CONTENT<>cnt_id=300681&FOLDER<>folder_id=162689&bmUID=1052357764487
- FDA.gov "Questions and Answers on Trans Fat Proposed Rule" http://vm.cfsan.fda.gov/~dms/qatrans.html