Special to CNN.com
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 significantly increases your risk of heart disease, the leading killer of men and women. Learn more 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, 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.
Initially, trans fats were thought to be a healthy alternative to animal fats because they're unsaturated and come primarily from plant oils. However, in 1990 scientists made a startling discovery: Trans fats appeared to both increase LDL cholesterol and decrease HDL cholesterol. More studies over the years confirmed this.
Trans fat in your food
Commercial baked goods — such as crackers, cookies and cakes — and many fried foods such as doughnuts and french fries — contain trans fats. Shortenings and some margarines also are high in trans fat.
Trans fat used to be more common, but in recent years food manufacturers have used it less. Since January 2006, manufacturers in the United States have been required to list trans fat content on nutrition labels. Manufacturers in other countries have taken similar steps. As a result, some companies have changed their manufacturing process to use little or no trans fat.
In the United States, the labeling requirement has a caveat. Trans fat that amounts to less than 0.5 grams per serving can be listed as 0 grams trans fat on the food label. 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" is also a clue: Shortening contains some trans fat.
It sounds counterintuitive, but "fully" hydrogenated oil doesn't contain trans fat. Unlike partially hydrogenated oil, the process used to make fully hydrogenated oil doesn't result in trans fatty acids. However, if the label says just "hydrogenated" vegetable oil, that usually means the oil contains 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.
Cholesterol levels are expressed as milligrams per deciliter of blood, or mg/dL:
* 160 mg/dL is considered a high LDL.
* 130 mg/dL and lower is a good target for most healthy people.
* 100 mg/dL is the target if you have other risk factors for heart disease.
* 70 mg/dL is the target if you already have heart disease.
With HDL cholesterol, higher is better. HDL helps remove excess cholesterol from your body. Higher levels of HDL are associated with a lower risk of heart disease.
* 40 to 50 mg/dL is normal for healthy men.
* 50 to 60 mg/dL is normal for healthy women.
* 40 mg/dL and lower for men or women is considered risky, and the lower the value, the greater the risk.
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 another 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, 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 — increases 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 many restaurants continue to use trans fat. Trans fat is often 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. But, things may be changing. New York City recently banned trans fat from being used in restaurants.
How much trans fat you can consume without any negative impact on your cholesterol level 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.
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 heart-healthy diet, 30 percent or less of your total daily calories can come from fat — but saturated fat should account for less than 7 percent of your total daily calories. Monounsaturated fat — found in olive, peanut and canola oils — is a healthier option. Nuts, fish and other foods containing unsaturated omega-3 fatty acids are other good choices.
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December 21, 2006
Tuesday, March 25, 2008