The Question Is…Which Fats Are Good For You?
It can be confusing to keep up with all the different kinds of fats that are listed on a nutrition fact panel. Remembering which fats are good for you and which ones you should avoid might require a Google search every time you’re looking at a new food. Going forward, this post will be all you need! Today, we’re gonna talk fats by breaking down the healthy fats and the bad fats. I’ll get a little nerdy on you and provide the basic scientific explanation as to why each of these fats are either good or bad, and hopefully make it a bit easier for you to remember in the future. We will also cover which foods contain good fats, and which foods you should avoid.
What is a fat molecule?
Before we dive into the difference between all the types of fats, we need to define a basic fat molecule. Fats are very long molecules, made mostly of carbon and hydrogen. These are called hydrocarbon chains. They have what’s called a carboxylic acid base, which includes a couple oxygen atoms. This is why you may also hear them called fatty acids. This is the basic structure of what a fat looks like. This also happens to be a basic saturated fat molecule.
Fats form into sticky, solid substances because of their intermolecular forces. Intermolecular means ‘between like molecules.’ The long hydrocarbon chains are attracted to each other, specifically the hydrogens. When you lay fats together, they can stack on top of one another allowing each hydrogen to interact with another hydrogen. The more hydrogen you have on the chain, the stronger the intermolecular forces. They are solids because the bonds are strong and don’t move or break away easily.
From a nutritional standpoint, all fats contain 9 calories per gram and are more caloric than the other macronutrients, protein and carbohydrates.
A Reasonably Healthy Fat: Saturated
A saturated fat is one that is ‘saturated with hydrogen.’ Hydrogen are bound only to carbon atoms in the hydrocarbon chain—not to each other. Let’s also remember that a carbon atom must have four bonds. In a saturated fatty acid, there are no available spots to bind another hydrogen in the hydrocarbon chain. This means that every carbon is bound to the next carbon in the chain with a single bond, and all other bonds are to hydrogen. This makes the hydrocarbon chains long and straight, allowing them to lay or stack on top of each other easily. And since fats interact with each other more strongly when there is more hydrogen, saturated fats have the strongest interactions and are solid at room temperature. An example of a saturated fat is shown above in Fig. 1.
So, why have I classified saturated fats as ‘reasonably’ healthy? We do need saturated fat in our diet, but their health risks have long been up for debate. In the past it has been argued that since these fats have strong interactions, they can more easily build up and clog arteries and lead to cardiovascular complications. However, more recent studies have shown that this is not necessarily true.  It is generally thought that these fats raise both good and bad cholesterol, but some long-term studies do not support a strong correlation.  There aren’t many concrete reasons to avoid them. In fact, many plant-based foods that are high in saturated fat have their own health benefits, like coconut oil. 
The only foods you want to avoid when consuming saturated fats are processed meats. A study has shown that while eating red meat does not increase your risk of heart disease, eating processed meats high in saturated fats does. 
Foods high in saturated fat:
- Red meats
- Coconut oil
A Very Healthy Fat: Unsaturated
Unsaturated fats are the good or ‘heart healthy’ fats. There are two types of unsaturated fats—monounsaturated and polyunsaturated. To determine the difference, we need to go back to the hydrocarbon chain. Since we’ve already defined a saturated fat, we can deduce that an unsaturated fat is one that is not saturated with hydrogen. This means that some carbons will have fewer hydrogens, resulting in double bonded carbons. An example of the fat structures are shown below.
Monounsaturated: one double bond
Polyunsaturated: more than one double bond
The difference between unsaturated fats and saturated fats is the structure or orientation of the hydrocarbon chain. You can see in Fig. 2 that these double bonds bend the hydrocarbon chain. Since these are bent, they don’t stack as easily and have fewer intermolecular forces. They are typically liquids in their pure form, and they are easier to metabolize. Unsaturated fats also lower bad cholesterol, or LDL (low-density lipoprotein).  Omega-3 fatty acids, which have a slew of health benefits, fall under the unsaturated fat category. 
Foods high in unsaturated fat:
- Peanuts and peanut oil
- Olive oil
Avoid These Fats: Trans fat
Trans fats are unsaturated fats, meaning they have double bonds in the hydrocarbon chains. The difference between naturally occurring unsaturated fats and trans fat is the way they are prepared. This is typically done by taking liquid vegetable oils and adding hydrogen to it, which creates solid fats that have longer shelf lives. Another name for trans fats are hydrogenated fats or oils. Since these are manufactured, and not natural, the double bonds found in the carbon chains are oriented differently. You saw above that natural unsaturated fats are bent. Trans fats are not. See the difference in the structures in Fig. 3.
The chains are straight because it takes less energy to produce a double bond with hydrogens on opposite sides. Since it is the ‘easier’ route, it will be the favored product of the reaction.
Trans fats are also more solid fats, and are long and straight, allowing them to stack easily. This difference in structure changes their melting points and gives them a longer shelf life, which is beneficial for the processed food industry. Some of these melting points are higher than human body temperature, meaning that they will stay solid when digested. GROSS. Although their structure is flat like saturated fats, trans fats are more difficult for enzymes in the body to grab onto and metabolize, so they stick around longer. Trans fats are linked to a slew of heart complications, which result from increased LDL levels and clogged arteries.  Basically, you should stay away from processed foods that have trans fats in them!
You should check anything processed, but these foods contain trans fats:
- Some types of chips
- Fast food french fries
- Many kinds of processed fried foods
- Many kinds of processed desserts, baked goods, frosting
- Margarine and Crisco
- Processed meats
- Microwaved popcorn
The Big Fat Truth
As does most nutrition advice, the key to healthy meals all comes down to eating whole foods and avoiding anything processed. You can easily prepare many of the above listed trans fatty foods in healthier ways. You can make your own french fries, or find restaurants like In and Out, that cook their fries in pure vegetable oil, making them free of trans fat. We are (thankfully) moving beyond the fat-fearing days to a more common understanding that fats are good for you, as long as you’re eating the right ones!