Fats can be found in foods such as meat, fish, seafood, dairy products, nuts, seeds and oils. Fats serve as an energy source. They prevent heat loss in extreme cold weather and protect organs against shock. They are responsible for making up part of our body cells and transporting fat-soluble vitamins such as vitamin A, D, E and K. However, there are many kinds of fats, including saturated fat, unsaturated fat and trans-fat. Their names are due to the different structure of fat molecules, and each of them have different effects to our body, too.

Fats are crucial in maintaining our body temperature (since it acts as a good insulator), making cell membranes (which is composed of phosphorus bilipid layers) and producing cholesterol, which controls the fluidity of cell membranes. However, choosing the correct type of fat to take in is quite essential.

There are three main types of fats: Saturated, unsaturated and trans fats. Here, the degree of saturation describes whether the fat molecule’s main carbon chain contain single bonds only. If all single bonds, then each carbon atom forming the backbone of the molecule is saturated. The word “trans” refers to the geometrical shape of the molecule, meaning the main chain forms a C-shape around one carbon-carbon double bond. 

So which type of fat is better? 
The answer has to do with the two types of cholesterols that different kinds of fat can produce. 

One of them is LDL cholesterol, or low-density lipoprotein cholesterol. This is the bad one, because LDL cholesterol may build up in the wall of arteries, leading to a decrease in blood flow through the artery and making the artery thick. Eventually, it leads to the blockage of arteries. Saturated fat and trans-fat cause this kind of cholesterol to form. Among these two, trans-fat is much more harmful, so we should take as little trans-fat as possible. 

Another cholesterol is called HDL cholesterol, meaning high-density lipoprotein cholesterol. This one however is quite good for our body, as it won’t block the blood vessel and it helps bringing excess cholesterol into the liver, where it is decomposed into fatty acids and glycerol. 

In what kinds of food will we find those different kinds of fats?
First let me introduce the bad one—trans-fat and saturated fat. 
Trans-fat, being the most harmful form of fat, is abandoned for usage in many countries. However, it’s still quite ubiquitous. The main source of trans-fat is called “hydrogenated oil”, which is an artificial ingredient which is found commonly on cakes, cookies and microwave popcorns. The trans-fat on cakes and cookies are often rich in those artificial cream, so be sure to select natural cream products for your birthday party. 

Saturated fat is primarily found in animal products like beef, pork, and high-fat dairy foods, like butter, margarine, cream, and cheese. High amounts of saturated fat also are found in many fast, processed, and baked foods like pizza, desserts, hamburgers, and cookies and pastries. These fats tend to more "solid" (think butter or lard) than healthier fats.

Unsaturated fat, being the good one, is divided into monounsaturated fat and polyunsaturated fat. “mono” and “poly” refers to the number of unsaturated carbon-carbon double bonds in the fat molecule, and both are good for our health. 
Monounsaturated fats are found in high concentrations in olive, peanut, avocado, canola oils and seeds such as pumpkin and sesame seeds. While polyunsaturated fats are mainly found in sunflower seeds, corn, soybean, walnuts and fish (salmon for example). The well-known “Omega-3” is within the family of polyunsaturated fats, and it can be found from the food ingredients above. It’s worth mentioning that our body cannot produce Omega-3 ourselves, so it’s strongly encouraged to take in fishes and nuts regularly!