Why do trans fat and saturated fat get such a bad rap?

Fat is good for you. Necessary for your health, even. When we eat fat that we obtain from plants or animals we supply the body with energy. Those ­calories we obsess about really are pure energy. Without them, we wouldn't have the gusto to chase the ice cream truck down the street. Fat also helps the body with other important functions, such as absorbing vitamins, controlling blood pressure and keeping us warm. In toddlers, fat is critical for development of the brain, the immune system and those pinchable, cherublike cheeks.

As we get older, though, we often consume more fat than we burn, and we get, well, fat. When we become overweight, getting into last year's jeans should be the least of our worries. Excess fat contributes to coronary heart disease, which can result in heart attacks or strokes. Storing too much fat also increases your risk of developing type 2 diabetes, gallbladder disease and even cancer [source: MedlinePlus].

But why exactly is saturated fat bad? You have two types of cholesterol -- LDL, the low-density lipoproteins usually known as the bad kind, and HDL, the high-density lipoproteins simply known as the good kind. While some fats, such as monounsaturated or polyunsaturated fats, don't raise your LDL level, saturated fats unequivocally do. Saturated fat raises our bad cholesterol level more than anything else we put in our bodies. These fats are generally solid at room temperature and earn their name from the fact that the fat molecule's carbon atoms are saturated with hydrogen atoms.

Saturated fats are naturally occurring and can be found in foods such as that marbled steak on your plate, the skin on your cooked chicken and the whole milk filling your glass. The problem is that not only do saturated fats raise your cholesterol level; they're usually found in foods that already have cholesterol in them, such as cheese, ice cream and beef.

Health experts advise limiting your intake of saturated fats to 7 percent of your total calories, or about 16 grams a day [source: AHA]. To put this in perspective, 1 tablespoon of mayonnaise has 1.5 grams of saturated fat, 1 cup of whole milk has 5 grams of saturated fat and, if you fix yourself a treat in the form of a breakfast sandwich with egg, cheese and sausage, that sandwich alone will have about 18 grams of saturated fat.

As you can see, one tasty breakfast can put you over the recommended daily limit. Cutting down on your intake of butter, margarine, whole milk, cheese and lard doesn't seem too difficult, but it's tricky because so many products are made with at least one of those ingredients. While it's easy to eliminate a daily piece of pie or leg of lamb from your diet, you should also keep an eye on cheese pizza, chocolate, pastries and breads.

Cooking with coconut oil or palm oil will also increase the amount of saturated fat in a meal. Try to use vegetable oils such as corn oil, olive oil or sunflower oil because these items contain unsaturated fats. Unsaturated fats won't send your cholesterol through the roof. In fact, they don't raise it all and may even lower it a little. Replacing some of the meats you eat with fish, beans and nuts will also lower your total intake of saturated fats.

In the next section, we'll talk about another type of fat that wholly deserves its bad rap -- trans fat.

There's a reason why cream cheese has such a nice, smooth, consistent quality to it when you open a new package. That block of cream cheese, along with lots of other foods, has likely been made with vegetable oil that's been altered.

Before food makers add vegetable oil to cookies, crackers, doughnuts, french fries and other stuff, they heat the vegetable oil (often soybean oil). Then, they force bubbles of hydrogen into the oil at high pressure. As the hydrogen atoms bond to the carbon atoms in the oil, the new substance -- partially hydrogenated oil -- becomes more solid. (If you fully hydrogenate the oil, it can become almost as hard as a rock.)

Partially hydrogenated vegetable oil is creamy and cheaper than butter, qualities that make it appealing for both food manufacturers and consumers. Using this altered oil increases the food's shelf life and decreases its greasy feel, but it's very, very bad for you.

This partially hydrogenated oil has another name: trans fat, or trans fatty acid. Trans fat is used in countless food items like biscuits, pizza dough and stick margarine, and it wreaks havoc on your heart over time. Not only do trans fats raise your bad cholesterol (LDL) levels, they simultaneously lower your good cholesterol. With less good cholesterol and more bad cholesterol, you become more likely to have hardened, clogged arteries. That bad cholesterol builds up as plaque on the inside of your artery, but it's not very stable. One day, a little piece of that plaque will break off, your body will try to clot up the nick in the artery, and it's Heart Attack City.

Before 1990 or so, ignorance was bliss. We were eating tons of trans fats for the same reason we once installed asbestos in our homes: It seemed to work, and we didn't know any better. Now the U.S. Food and Drug Administration recommends that you eat less than 2 grams of trans fats per day. For perspective, a single donut can have as much as 5 grams of trans fat [source: Davis].

Increased awareness of the dangers of trans fats and several lawsuits have led many fast-food restaurants (most famously KFC) to switch to nonhydrogenated cooking oils. Many cities, such as New York, and even one state, California, have banned the use of hydrogenated oils in restaurants. Interestingly, some trans fats are found naturally in beef, lamb and butterfat, but experts aren't sure if these natural trans fats produce the same negative health effects.

Many packaged food items in your grocery store will have "No Trans Fats!" boldly splashed across the front of the box. In the dietary information on the back of the box, you see it again -- "Trans fats … 0 g." But incredibly, when you look at the list of ingredients, there it is: "Partially hydrogenated soybean oil." What gives? That's trans fat, right? Right. Food manufacturers can label their products as having no trans fats if they contain less than half a gram per serving.

Your best bet is to scan the list of ingredients and look for shortening or partially hydrogenated soybean oil. If they're listed, you're about to dive into some trans fats, no matter how much the rest of the packaging denies this fact.

Limiting or cutting trans fats and saturated fats out of your diet will go a long way toward keeping that beautiful heart of yours nice and healthy. Continue reading for lots more information on saturated fats, trans fats and heart health,­ and to learn if the cure for heart disease is one carrot away.