Trans fat is double trouble for your
heart health
Trans fat raises your
"bad" (LDL) cholesterol and lowers your "good" (HDL) cholesterol. Find
out more about trans fat and how to avoid it.
By Mayo Clinic staff
When it comes to fat, trans fat is considered by some doctors to be
the worst of them all because of its double-barreled impact on your
cholesterol levels. Unlike other fats, trans fat — also called
trans-fatty acids — both raises your "bad" (LDL) cholesterol and lowers
your "good" (HDL) cholesterol.
A high LDL cholesterol level in combination with a low HDL
cholesterol level increases your risk of heart disease, the leading
killer of men and women. Here's some information about trans fat and how
to avoid it.
What is trans fat?
Trans fat comes from adding hydrogen to vegetable oil through a
process called hydrogenation. Trans fats are more solid than oil is,
making them less likely to spoil. Using trans fats in the manufacturing
of foods helps foods stay fresh longer, have a longer shelf life and
have a less greasy feel.
Trans fat in your food
Commercial baked goods — such as crackers, cookies and cakes — and
many fried foods, such as doughnuts and french fries — may contain trans
fats. Shortenings and some margarines can be high in trans fat.
Trans fat used to be more common, but in recent years food
manufacturers have used it less because of concerns over the health
effects of trans fat. Food manufacturers in the United States and many
other countries list the trans fat content on nutrition labels.
However, you should be aware of what nutritional labels really mean
when it comes to trans fat. For example, in the United States if a food
has less than 0.5 grams of trans fat per serving, the food label can
read 0 grams trans fat. Though that's a small amount of trans fat, if
you eat multiple servings of foods with less than 0.5 grams of trans
fat, you could exceed recommended limits.
Reading food labels
How do you know whether food contains trans fat? Look for the words
"partially hydrogenated" vegetable oil. That's another term for trans
fat. The word "shortening" also is a clue: Shortening contains some
trans fat.
It sounds counterintuitive, but "fully" or "completely" hydrogenated
oil doesn't contain trans fat. Unlike partially hydrogenated oil, the
process used to make fully or completely hydrogenated oil doesn't result
in trans-fatty acids. However, if the label says just "hydrogenated"
vegetable oil, it could mean the oil contains some trans fat.
Although small amounts of trans fat occur naturally in some meat and
dairy products, it's the trans fats in processed foods that seem to be
more harmful.
Trans fat and cholesterol
Doctors worry about trans fat because of its unhealthy effect on your
cholesterol levels — increasing your LDL and decreasing your HDL
cholesterol. There are two main types of cholesterol:
- Low-density lipoprotein (LDL). LDL, or "bad,"
cholesterol transports cholesterol throughout your body. LDL
cholesterol, when elevated, builds up in the walls of your arteries,
making them hard and narrow.
- High-density lipoprotein (HDL). HDL, or "good,"
cholesterol picks up excess cholesterol and takes it back to your
liver.
A high LDL cholesterol level is a major risk factor for heart
disease. If your LDL is too high, over time, it can cause
atherosclerosis, a dangerous accumulation of fatty deposits on the walls
of your arteries. These deposits — called plaques — can reduce blood
flow through your arteries. If the arteries that supply your heart with
blood (coronary arteries) are affected, you may have chest pain and
other symptoms of coronary artery disease.
If plaques tear or rupture, a blood clot may form — blocking the flow
of blood or breaking free and plugging an artery downstream. If blood
flow to part of your heart stops, you'll have a heart attack. If blood
flow to part of your brain stops, a stroke occurs.
Other effects of trans fat
Doctors are most concerned about the effect of trans fat on
cholesterol. However, trans fat has also been shown to have some other
harmful effects:
- Increases triglycerides. Triglycerides are a
type of fat found in your blood. A high triglyceride level may
contribute to hardening of the arteries (atherosclerosis) or
thickening of the artery walls — which increases the risk of stroke,
diabetes, heart attack and heart disease.
- Increases Lp(a) lipoprotein. Lp(a) is a type of
LDL cholesterol found in varying levels in your blood, depending on
your genetic makeup. It's unclear how high levels of Lp(a) —
independent of other cholesterol levels — increase your risk of
heart disease. More research is needed.
- Causes more inflammation. Trans fat may
increase inflammation, which is a process by which your body
responds to injury. It's thought that inflammation plays a key role
in the formation of fatty blockages in heart blood vessels. Trans
fat appears to damage the cells lining blood vessels, leading to
inflammation.
Avoiding trans fat
The good news is trans fat is showing up less in food, especially
food on grocery store shelves. If you eat out a lot, however, be aware
that some restaurants continue to use trans fat. Trans fat is sometimes
a part of the oil restaurants use to fry food. A large serving of french
fries at some restaurants can contain 5 grams or more of trans fat.
Some restaurants put nutritional information on their menus, but most
aren't required to list trans fat content. Some cities, such as New York
City, have banned restaurants from using trans fat.
How much trans fat you can safely consume is debatable. However,
there's no question you should limit trans fat, according to the Food
and Drug Administration and the American Heart Association (AHA).
In the United States, food nutrition labels don't list a Percent
Daily Value for trans fat because it's unknown what an appropriate level
of trans fat is, other than it should be low. The AHA recommends that no
more than 1 percent of your total daily calories be trans fat. If you
consume 2,000 calories a day, that works out to 2 grams of trans fat or
less, or about 20 calories.
What should you eat?
Don't think a trans fat-free food is automatically good for you. Food
manufacturers have begun substituting other ingredients for trans fat.
However, some of these ingredients, such as tropical oils — coconut,
palm kernel and palm oils — contain a lot of saturated fat. Saturated
fat raises your LDL cholesterol. A healthy diet includes some fat, but
there's a limit.
In a healthy diet, 25 to 35 percent of your total daily calories can
come from fat — but saturated fat should account for less than 10
percent of your total daily calories. Aim for consuming less than 7
percent of your fat calories from saturated fat if you have high levels
of LDL cholesterol.
Monounsaturated fat — found in olive, peanut and canola oils — is a
healthier option than is saturated fat. Nuts, fish and other foods
containing unsaturated omega-3 fatty acids are other good choices of
foods with monounsaturated fats.
May 7, 2009
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