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. Trans fats make Lp(a) into smaller and denser lipid particles, which promotes a buildup of plaques in your arteries.
  • 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.

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 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 food that is free of trans fat 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. 06, 2011 See more In-depth