Polyunsaturated Fats, Saturated Fats, and Trans-Fats
Polyunsaturated fats are found in certain fish such as salmon and tuna, as well as in soybean oils. This group of fats includes the omega-3 and the omega-6 fatty acids, also known as essential fatty acids because your body can't manufacture them and they must be consumed through eating. These fats play several critical roles in your body, including fostering healthy growth of cells.
Saturated fats differ from unsaturated fats in that they are typically solid at room temperature, whereas unsaturated fats are typically liquids (such as oils). Butter is a typical example of a food high in saturated fat. Saturated fats are generally found in meat and dairy products. Eating saturated fats tends to raise the levels of both good and bad cholesterol in your body, and diets high in saturated fats have been implicated in increased risk of heart disease. You don't actually need to consume any saturated fats—your body manufactures all the saturated fats it needs.
Finally, we come to trans-fats. These are an entirely man-made, un-natural phenomenon. And though you may not realize it, trans-fats are found in many, many manufactured and processed foods consumed by most people.
Trans-fats are derived from unsaturated fats through a process called hydrogenation, which involves heating the unsaturated fats in the presence of hydrogen to load extra hydrogen atoms into the fats. These fats were invented to give unsaturated fats a property important for food companies: it makes them solid at room temperature and allows the companies to make fat-filled foods with a solid form and a long shelf-life.
Trans-fats are also cheaper ingredients for food companies. Most margarines are full of trans-fat, and shortening is pure trans-fat. Many packaged cookies and pastries are packed with trans-fats, fast foods (especially French fries) are packed with trans-fats, and potato chips are often loaded with trans-fats too.
Be sure to read the labels on your food to see if they have the words hydrogenated oil or partially hydrogenated oil on the package. If they do, don't purchase these products—they contain trans-fats. Because of the dangers of trans-fats, the FDA required food labels to break out the number of grams of trans-fats in foods in 2006.
Why are trans-fats harmful? They actually have the opposite effect of monounsaturated fats: they raise levels of the bad cholesterol in your body and lower the levels of good cholesterol in your body. It is also hypothesized that trans-fats may contribute to degenerative diseases by interfering with a cell's ability to process healthy fats. This illustrates that not all of the impacts of trans-fats on the body have been fully researched or discovered yet, but rather they are the subject of active scientific research. Because they are man-made chemicals and relatively new, we may yet discover that trans-fats have many other harmful effects as well.