By Roberta H. Anding, MS, Baylor College of Medicine and Texas Children’s Hospital

Edited by Kate Findley and proofread by Angela Shoemaker, The Great Courses Daily

Saturated, polyunsaturated, monounsaturated—what does it all mean? Professor Anding explores the different types of fat, both on a chemical and practical level, and delves into the notorious trans fats.

What Is Fat?

By understanding the different types of fats and how they work in your body, you can better parse out fact from fiction when it comes to nutritional trends. Fats are also known as lipids, and they are the most energy dense of all the macronutrients at nine calories a gram. Carbohydrate and protein, by contrast, both have four. 

This is true for all fats, whether it’s heart-healthy olive oil or lard. Thus, keep in mind that “light” olive oil is not light in calories but in color. 

Dietary fat can be visible, such as the fat found in mayonnaise, margarine, or cooking oil, or invisible fats found in muffins, nuts, cookies, desserts, and cheeses. Many people are surprised to know that nuts contain anywhere between 60% and 70% fat. 

Chemically, fats are made up of three elements: carbon, hydrogen, and oxygen. Different types of fats are structurally different from one another, and because they are structurally different, they don’t behave the same way. 

Dietary fats are made up of three fatty acids stuck, or esterified, to a glycerol backbone. It looks like the letter “E.” There’s a backbone with three prongs sticking out, and those are your fatty acids.

Saturated Fats

When we hear the term “saturated fats,” it means that in this long carbon fatty-acid chain, there’s no double bond and no space. The whole molecule is saturated with hydrogen ions.

Saturated fats are hard, white, and solid in their visible form. When you go to the grocery store and buy a steak, the hard, white coating on the outside is saturated fat. 

Coconut oil and palm oil are common ingredients, and the word “oil” gives the impression that you can pour it, but you can’t. It’s a solid, plant-based fat. 

When you buy mint chocolate chip ice cream, for example, the crunchy chocolate pieces in that ice cream actually are made with coconut oil or palm oil because the colder the fat gets, the more solid it becomes. Overall, saturated fats can raise your blood cholesterol in a predictable fashion. 

Types of Unsaturated Fats

“Unsaturated fat” means that there are double bonds that exist between the carbon molecules. Polyunsaturated fats consist of two or more double bonds, and because these double bonds have space between them, they can combine with oxygen and become rancid. If you’ve ever eaten a food with fat in it that has an off taste, that taste is rancid polyunsaturated fat. 

Polyunsaturated fat is liquid at room temperature. It includes corn oil, safflower oil, and sunflower oil. These fats are considered heart-healthy and can actually lower blood cholesterol. 

Monounsaturated fat compounds have only one double bond and are also liquid at room temperature, but they get thick or viscous when you put them in the refrigerator. These fats include olive oil and peanut oil, and they are considered beneficial for heart health.

Trans Fats

We hear a lot about trans fats in the media. Trans fats are unsaturated vegetable oils that manufacturers try to make more solid in order to preserve the shelf life of the food. This type of fat is less likely to become rancid because it contains fewer double bonds. 

Manufacturers make it solid at room temperature through a process known as “hydrogenation,” where they blow hydrogen gas into unsaturated fat. They add hydrogen to those double bonds, changing the shape of the fatty acid chain.

When the shape and structure change, so does the function. These fats are listed as “partially hydrogenated fats” on the label and can be found in premade foods such as muffins and cookies. 

Current research shows that trans fats are just as likely to contribute to heart disease as saturated fat. In fact, some researchers suggest that this fat is the major villain in the development of coronary artery disease. 

Since 2006, food manufacturers have been required to list their products’ trans fat content on the label. However, the way the labeling law is stated, portions with less than 0.5 grams of trans fats per serving are allowed to be labeled “trans fat free,” so you need to check the portion on the label. Some manufacturers resort to tricks such as making the portion size smaller in order to reduce the trans fat content to less than 0.5 gram per serving and have a “trans fat free” label.

Triglycerides are an important type of dietary fat because more than 90% of the fat in our body and most of the fat in our food is in this form. When we store extra calories as body fat, we are storing it in the form of triglycerides. 

Now when you see a study in the media that mentions any of these types of fats, you’ll understand the terminology. You’ll also be able to better assess whether or not you can trust the conclusions.

This article was edited by Kate Findley, Writer for The Great Courses Daily, and proofread by Angela Shoemaker, Proofreader and Copy Editor for The Great Courses Daily.

Professor Roberta H. Anding is a registered dietitian and Director of Sports Nutrition and a clinical dietitian at Baylor College of Medicine and Texas Children’s Hospital. She also teaches and lectures in the Baylor College of Medicine’s Department of Pediatrics, Section of Adolescent Medicine and Sports Medicine, and in the Department of Kinesiology at Rice University.