Health experts are quick to point out the advantages of unsaturated fats over saturated or trans fats when following heart-healthy diets, but what exactly are unsaturated fats, and why are they considered healthier than other forms of fat? To fully understand what unsaturated fats are, we're going to have to take a trip back to organic chemistry class, wiseGEEK style. There will not be a short quiz at the end, however.

Unsaturated fats are almost always plant-based, although there are some naturally unsaturated fats in certain meats. These unsaturated fats are perhaps better known as vegetable oils, since they remain in a liquid or oily state at room temperature. This fact becomes important when trying to understand the ongoing health debate over saturated, trans and unsaturated fats. Unsaturated fats such as the olive oil or canola oil in your kitchen cabinet will eventually turn rancid as oxygen molecules from the air mix with the hydrogen and carbon atoms in the fat. This is why commercial food producers do not use many unsaturated fats in their products. Products made with unsaturated fats, such as cookies or fried snacks, would only last a few days on store shelves.

Here's where the organic chemistry lesson begins. Unsaturated fats and saturated fats are essentially composed from the same raw ingredients, including carbon and hydrogen atoms. Saturated fats, such as the fat formed in animals, contain chains of carbon atoms with single bonds to hydrogen atoms. Think of it as a carbon centipede with just the right number of hydrogen shoes on its feet. Because the chain of fat contains all the hydrogen it can hold, it is considered to be fully saturated with hydrogen. The result is a solid fat product, like butter or lard.

Unsaturated fats, on the other hand, would be like a carbon centipede who forgot to put on some hydrogen boots but put two feet in others. The result is a chain of fat missing a few hydrogen atoms, which keeps it unstable and ripe for attack from oxygen atoms. This form of fat is considered to be unsaturated, because it has not taken on all the hydrogen it can hold. Unsaturated fats remain liquid at room temperature because of this incomplete bonding process. This is also what makes cooking oils ideal for certain recipes and cooking processes, since they do not solidify as easily as saturated fats.

The reason why unsaturated fats are considered healthier than saturated or transfats is the nature of the fat molecules once they reach the bloodstream. Saturated or trans fat molecules have a natural tendency to bond with each other on contact, which eventually leads to the formation of artery-clogging plaque. Unsaturated fats, however, have larger molecules and tend to slide past each other in the bloodstream, which means little to no plaque build-up. While it may be unwise to eliminate all saturated fats from one's diet, switching to unsaturated fats such as olive or canola oils for cooking purposes does make sense.

One troubling use of unsaturated fats, however, is as the base for a stabilization process called hydrogenation. Remember that unsaturated fats still have room to accommodate hydrogen atoms. By bubbling pure hydrogen gas through tanks of unsaturated fats, a new form of fat is formed called transfat, or partially hydrogenated vegetable oil. This new form of fat combines the stability and solidity of saturated fats with the cost benefits of unsaturated fats, but is also responsible for increased plaque formation. Consumers seeking a truly healthy diet should avoid partially hydrogenated oils altogether and limit daily fat intake to less than 30% of the total calorie count.