Stealth Fats: How Food Makers Hide Them From You
For: How Bad Are Tropical
Oils, January 2003
By now most Americans have heard of trans fats,
but they actually know little about them. You may have first become aware
of them in the mid-1990s, when reports began to surface that margarine,
often touted as healthy, contains these sinister fats and may not be preferable
to butter after all. It turned out that trans fats were in most processed
foods in the supermarket and in many fast foods. In 1994 Harvard researchers
went so far as to conclude that trans fats were responsible for more than
30,000 of the country's annual deaths from heart disease. Other scientists
dismissed these fears as overblown, and since then the debate has continued.
Here's the latest.
What are trans fats and why are they added
to foods?
Manufacturers partially hydrogenate—that
is, add hydrogen to—corn, soybean, and other highly unsaturated oils
to make them more solid and stable. The result: some of the polyunsaturated
and monounsaturated fatty acids in the oils become more saturated. This
process also transforms the chemical structure of some unsaturated fatty
acids in other subtle ways, producing trans fatty acids (or simply trans
fats). Hydrogenation gives margarines, shortening, and puddings a creamy
consistency, and prolongs the shelf life of crackers, cakes, cookies,
chips, popcorn, chocolate candy, and other foods that contain the semi-solid
oils. Because they are less likely to turn rancid, hydrogenated oils are
also often used for deep-frying in fast-food restaurants.
Why are trans fats bad?
While regular unsaturated fats lower blood
cholesterol, trans fats act more like saturated fats—raising total
and LDL ("bad") cholesterol. In addition, in a sort of double
whammy, trans fats lower protective HDL ("good") cholesterol,
which makes them, overall, even worse than saturated fats. They may also
increase the risk of heart disease in other ways: for instance, they boost
blood triglyceride levels and seem to impair the ability of blood vessels
to dilate. They have also been linked to an increased risk of diabetes.
A 1993 study of nearly 90,000 women found that
those who ate the most foods high in trans fats (especially margarine)
had a more than 50% higher risk of heart disease than women who rarely
ate these fats. Two recent Dutch studies also found increased coronary
risk among people consuming high levels of trans fats.
How much trans fats do we eat?
One estimate is that trans fats provide 2 to
4% of our total daily calories, but other estimates are higher. The fact
is, no one really knows. Moreover, any such average means little, since
some of us consume little or no trans fats, while others consume two or
three times the average. A large order of fast-food fries, for instance,
or a frosted donut by itself can put you over the average. In addition,
food manufacturers often change the types of oils they use and the degree
of hydrogenation of the oils, so it's impossible to keep track. And food
labels don't help (see below).
Many researchers believe that since trans fats
make up only a small portion of our fat intake, worries about them are
exaggerated. It is true, however, that during the past 15 years we've
been consuming more and more trans fats, since food makers have been using
more hydrogenated oils.
Is there any way to tell from the label
how much trans fat is in a food?
No. If you see partially hydrogenated oil on
the ingredients list, you know the food contains some trans fats. But
nutrition labels don't specify how much. This may actually encourage manufacturers
to use hydrogenated oils, since unlike the saturated fats they often replace,
the trans fats remain invisible on nutrition labels. And trans fats are
not currently counted as saturated fat on labels.
Three years ago the FDA proposed adding the
trans fats content to nutrition labels, but the process has been put on
a back burner. As things stand, foods that contain trans fats are even
allowed to make heart-healthy claims. For instance, Triscuit crackers
are high in trans fats, yet the box boasts "no cholesterol"
and "low saturated fat." Labeling of
trans fats is long overdue.
Some things are clear
• You needn't worry about occasionally eating small amounts of margarine (or, for that matter, butter, which is rich in saturated fat but contains no trans fats). However, if you eat lots of margarine, try to use less, or switch to a more healthful type. The more solid the vegetable oil, as in stick margarine, the more hydrogenated it is, and therefore the more artery-damaging trans fats it has. Tub margarines are soft and contain lots of unaltered polyunsaturated fats, which actually help lower blood cholesterol. "Diet" margarines are softest and have more water—and less than half the fat of other margarines. Liquid "squeeze" margarines are also good alternatives.
• Even if you don't eat margarine, you may be consuming lots of trans fats. Processed and fast foods that contain partially hydrogenated oils supply more than two-thirds of the trans fats in the American diet. If you eat these foods often, cut back. Trans fats are only one of the nutritional strikes against them.
Promising developments:
Food makers, especially in Europe, have been finding new ways to reduce
trans fats in foods. In this country, margarine makers have been reformulating
many products to cut down on trans fat (and total fat). And the USDA has
developed a new process called low-trans hydrogenation, which produces
fewer trans fats and may soon be used for margarines and other spreads.
UC Berkeley Wellness Letter, April 2002