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Just when you thought you knew which types of fats to watch
out for on nutrition labels, you begin hearing about "trans
fats", and they're not even mentioned on the label!
Trans fats are formed during a process in which vegetable
oils are heated and exposed to hydrogen gas. This process, called
hydrogenation, changes the structure of the fat in some places
along its carbon backbone. The added hydrogen exerts a slight
pull that rotates the fat chain, changing the configuration from
what in chemistry is called "cis" to "trans." Thus the name trans
fats. The process is done to improve the texture and keeping
quality of oil-based fats.
Trans fats also occur naturally, mainly in meat and dairy
products. Overall, trans fats make up from 2 to 4 percent of the
calories in our diet, compared to 12 percent for saturated fats
and 30 percent for total fats.
Hydrogenated fats are nothing new. In 1911, cottonseed oil
was first hydrogenated in the United States to produce vegetable
shortening as a replacement for lard. The manufacturing process
became more established in the 1930s as margarine entered the
scene. As diets high in saturated fat became more strongly
associated with high blood cholesterol and elevated risk of heart
disease, more people began switching to lower saturated-fat
products like vegetable margarine.
And, research has shown this was a good change. In the past
30 years since low saturated fat diets have been advocated, there
has been steady progress in reducing the overall risk of
developing heart disease among Americans. However, a spate of new
research has brought trans fats into the limelight, conjuring
confusion about the best recommendations for fat intake and heart
disease once again.
Specifically Consumers are asking, "What's better for your
heart, butter or margarine?" While most researchers still agree
margarine is better, they recommend tub margarines over stick
varieties to reduce the level of trans fats, and recommend
spreading both butter and margarine lightly to lower overall
calories from fat.
The evidence that saturated fat, like that found in butter,
raises total and LDL cholesterol, or bad cholesterol, is still
intact. What the new evidence on trans fats says is that
Consumers at risk of heart disease need to be careful not to
replace the saturated fat in their diets with foods high in
hydrogenated oils, a mistake that's all too easy to make.
Processed foods marketed low cholesterol and low in saturated fat
are often the very foods high in trans unsaturated fats.
While there's no category for trans fats on the nutrition
panel, foods high in trans fats are those that list partially
hydrogenated vegetable oil on the ingredient list.
Common sources of trans fats include stick margarines,
savory and fried snack foods such as crackers, potato chips and
corn chips, and baked goods and pastries including packaged
cookies, doughnuts and desserts.
The skinny on fats? Most experts emphasize reducing fat in
general and replacing saturated fats in the diet with fats shown
to have a beneficial effect on cholesterol levels. These are the
non-hydrogenated polyunsaturated and monounsaturated vegetable
oils. Polyunsaturated fats include safflower, corn and soybean
oils; monounsaturated fats include olive and canola oils.
For more information, contact your local
Colorado State University Extension office.
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