From CopperWikicooking oils are treated with hydrogen to give longer shelf and better taste and texture to food products. Most of the French fries, fried chicken baked croissants, cookies, and donuts available in the market are made using partially hydrogenated vegetable oils.
The process of hydrogenating oil is not very old. Discovered around the turn of the 20th century, it became the first man-made fat to join the food supply. Trans fat gained widespread popularity during World War II, when many people began using margarine and shortening as alternatives to rationed butter.
 Why should I be aware of this?
- Trans fat 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 United States' labeling requirement states that 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 is 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.
- Only when the food label states "no trans fats" does it really mean there are none.
- According to the U.S. Food and Drug Administration, adult Americans on average consume about 5.8 grams of trans fats or 2.6% of calories, per day. Medical research shows that the daily intake of about 5 grams of trans fat is associated with a 25% increase in the risk of heart disease.
- Oil that contains trans fat stays stable for long periods, so the same oil can be used for longer periods of time. Regular oil goes rancid fairly quickly, and many restaurants would need to buy more oil than they currently do
- Trans fats is not just restricted to restaurant foods. They are also present in nearly every kitchen.
- Even if the menu boasts that items are "cooked in vegetable oil," that does not necessarily mean they are trans- fat-free foods. They may contain some partially hydrogenated vegetable oil.
 All about trans fats
Trans fat is usually formed when hydrogen is added to vegetable oil through a process called hydrogenation. A small amount of trans fat is found naturally, primarily in some animal-based foods. Foods cooked in hydrogenated oils have longer shelf life, more stable flavor and taste.
 Some sources of trans fat
- French fries
- Pastries (also high in saturated fats)
- Hard margarine
- Vegetable shortening
- Cookies (also high in saturated fats)
 FDA guidelines
According to the U.S. Food and Drug Administration (FDA) labeling guidelines, if a food contains 0.49 grams of trans fat in 1 serving, that food will have "Trans Fat: 0 grams" listed in its nutrition facts.
Few people ever eat 1 serving of anything. So, if someone happened to eat 2 servings of a food that contained 0.49 grams of trans fat per serving, they would actually be eating just under 1 full gram of trans fat all while thinking they ate "0 grams." Manufacturers also adjust their serving size until they get it to a point where they reach the 0.49 grams of trans fat (or lower) level. This allows them to put "0 grams" on their label.
Only when the food label states "no trans fats" does it really mean there are none.
Moreover, there is a possibility that a food product that claims zero trans fat, might haves 20 grams of saturated fat in one serving. So even though it has no trans fats, it contains a day's worth of saturated fat and is anything but healthy
 What can I do?
- Avoid products containing "partially hydrogenated fats or oils" (the main source of trans fats) or "shortening."
- Keep in mind that some manufacturers are listing components of food ingredients separately so they can move trans fats lower on the list of ingredients.
- Though trans fats are the worst fats, even more so than saturated fats, but you must evaluate a food on the entire profile, including calories, total fat, saturated fat, vitamins, mineral, sodium, sugar, and fiber, before going ahead.
- Look for trans fat substitute on food labels and ask eateries about what cooking medium are they using while eating out.
 Healthy oil subsitutes
 Non healthy oil substitutes
- Palm oil
- Coconut oils
- Other tropical oils which solidify at room temperature, contain higher levels of saturated fatty acids.
 Trans fat and health
Apart from the effect of trans fat on cholesterol, trans fat also has other harmful effects:
- It increases triglycerides which can in turn lead to the hardening of the arteries (atherosclerosis) or thickening of the artery walls. This increases the risk of stroke, heart attack and heart disease.
- Trans fat increases lipoprotein. Lipoprotein is a type of LDL cholesterol found in varying levels in the blood.
- Trans fat appears to damage the cells lining blood vessels, leading to inflammation.
- Trans-Fat-Free Food: What's the Truth?
- Revealing Trans Fats:US Fod And Drug Administration
- Why McDonald's Isn't Free of Trans Fat:Business Week
- The Top 10 Trans-fat Foods:Business Week
- Can You Name 3 Trans Fat Foods?
- Trans fat: Avoid this cholesterol double whammy