[Top: A nutritionist with Singapore's Ministry of Health teaching participants how to read food labels]

TRANS fat is the result of adding hydrogen to vegetable oil through a process called hydrogenation. Trans fats are more solid than oil, making them less likely to spoil.

Foods produced with trans fat stays fresh longer, with a longer shelf life and a less greasy feel.

Initially, trans fats were thought to be a healthy alternative to animal fats because they are unsaturated and come primarily from plant oils.

However, in 1990, scientists discovered that trans fats appeared to increase LDL cholesterol and decrease high-density lipoprotein (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 fat. Shortenings and some margarines also are high in these fats.

Trans fat used to be more common, but in recent years food manufacturers are using less of it.

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 US, United States, the labelling 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.

It is a small amount but if you eat multiple servings of foods with less than 0.5 grams of trans fat, you could exceed the recommended limit.

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.

However, "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 plaque - can reduce blood flow through your arteries. If your coronary arteries are affected, you may have chest pains 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 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 is 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

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 per cent or less of your total daily calories can come from fat, but saturated fat should account for less than seven per cent 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.

- Source: www.mayoclinic.com/health/trans-fat

This story was first published in New Straits Times.