This is the first installment of a video series highlighting the basics of several nutrition topics in partnership with Osmosis, an organization that focuses on health science education. You can view a playlist of our video collaborations with Osmosis here.
Fats are an essential part of a healthy diet—they’re involved in everything from providing us with a major source of energy, to helping us absorb vitamins, to refereeing communication between the cells in our bodies. As if these health benefits weren’t enough, fats also contribute to our enjoyment of food by adding taste and texture—like the smoothness of guacamole, or the flakiness of a croissant.
The Basics of Dietary Fats: Chemical Structure and Naming
Dietary fats usually have a three-carbon backbone—called glycerol—attached to one or more fatty acid chains, which are basically strings of carbon and hydrogen atoms. If there are three fatty acid chains, the structure is called a triglyceride. If there are only one or two fatty acid chains, the structure is called a monoglyceride or a diglyceride, respectively.
There are various types of fatty acid chains, and one way to categorize them is by their length. Short-chain fatty acids (SCFAs) have up to six carbon atoms. They can be found in dairy products and are also produced by our gut microbiome. Medium-chain fatty acids, like some of the fats found in coconut oil, have seven to 12 carbons. And long-chain fatty acids, like oleic acid in olive oil, have 13 or more carbon atoms in their fatty acid chains.
Fatty acid chains are also categorized by whether they have single or double bonds connecting their carbon atoms. When a fatty acid has only single bonds, it’s called a saturated fatty acid because it has as many hydrogen atoms as possible—that is, it’s saturated with them! Triglycerides with saturated fatty acids are straight in shape and thus pack together very well; as a result, they’re usually in solid form at room temperature. When a fatty acid has one or more double bonds, it’s called an unsaturated fatty acid because it’s not saturated with hydrogen atoms.
Different Types of Dietary Fats
There are a few distinct categories of dietary fats, each of which has different structures and roles in the human body. Even though some foods are often associated may be higher in one type of dietary fat, keep in mind that all foods with fat contain a blend of fatty acids.
Saturated fats are typically solid at room temperature. This is because triglycerides are straight and pack together well when paired with saturated fatty acids. The longer the saturated fatty acid chain, the more likely it will be solid at room temperature. Examples of foods with higher amounts of saturated fat include butter, coconut oil, full-fat dairy products, high-fat meats, and baked goods like pastries, cookies, and biscuits. Dishes with many ingredients, like pizza, burgers and casseroles, often have ingredients that are high in saturated fats.
The impact of saturated fat on cardiovascular health is somewhat complex. The Dietary Guidelines for Americans recommend limiting the overall intake of saturated fat to less than 10% of daily calories for people age 2 and up, due to its association with higher blood concentrations of LDL (“bad”) cholesterol. High levels of LDL cholesterol increase the risk for heart attack, stroke, and other health issues. However, evidence suggests that different types of saturated fatty acids may affect our cardiovascular health in different ways. The health impacts of reducing or replacing saturated fat in the diet may depend on the nutrients that replaces it. For example, replacing saturated fat with polyunsaturated fat has been shown to benefit cardiovascular health, but replacing saturated fat with monounsaturated fat has not.
Trans fatty acids are a type of unsaturated fatty acid that have hydrogen atoms on the opposite side of the double bond—roughly diagonal from each other. This structure is different from that of most other unsaturated fats, which have hydrogen atoms on the same side of the double bond (called a cis configuration). Because the fatty acid chain is straighter in the trans configuration, trans fats are typically solid at room temperature, like saturated fats. Small quantities of trans fats are found naturally in meat and dairy products. They can also be artificially created through the partial hydrogenation of liquid oils, although partially hydrogenated oils have been largely removed from foods in North America and Europe because trans fats have been associated with coronary heart disease.
Unsaturated fats tend to have a bend in their structure due to their carbon double-bond(s)—similar to how an arm bends at the elbow. This means they can’t pack together as tightly, and as a result, food items that have a higher proportion of unsaturated fats, like cooking oils, are usually liquid at room temperature. This is why olive oil is easily pourable at the same temperature that a stick of butter, which is higher in saturated fat, needs to be cut with a knife.
There are two types of unsaturated fats: monounsaturated fats (MUFAs) and polyunsaturated fats (PUFAs).
Monounsaturated fats (MUFAs) have one carbon double bond (“mono” = one). MUFAs are found in both plant and animal foods. Foods with higher MUFA content include plant-derived oils (especially olive and canola oils, but also safflower, sunflower, peanut, and sesame oils), avocados, olives, nuts, nut butters, and seeds. MUFAs are a key part of the Mediterranean diet, of which olive oil is a staple food. Animal-derived MUFAs are found in meats, fish, and dairy foods like yogurt and milk.
Observational studies have demonstrated that MUFAs may have an especially positive impact on cardiovascular health when used to replace saturated and trans fats in the diet. These effects include helping to lower LDL (“bad”) cholesterol while maintaining HDL (“good”) cholesterol and improving blood vessel function. One study found that replacing 5% of energy from saturated fat with MUFAs was associated with a 15% lower risk of coronary heart disease and another found that replacement of saturated fat with MUFAs (mainly from plant sources) decreased CHD risk.
Polyunsaturated fats (PUFAs) have more than one carbon double bond (“poly” = many). There are many different types of PUFAs, with the most common varieties in our diet being omega-3 and omega-6 fatty acids. Omega-3s come from plant sources like flaxseed, chia seed, walnuts, and canola and soybean oils. Cold-water fatty fish (like salmon, herring, sardines, and mackerel) are important sources of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), two important omega-3 fatty acids.
Omega-6 fatty acids include arachidonic and linoleic acid. Sources of linoleic acid include vegetable oils, nuts, and seeds; arachidonic acid is found in meat and eggs. You can read more about omega-3 and omega-6 fatty acids here.
PUFAs are associated with lowering blood pressure and helping to reduce total and low-density lipoprotein (LDL) cholesterol, which is linked to lower rates of cardiovascular diseases like heart attacks and strokes. EPA and DHA help lower plasma triglyceride levels, which protects against cardiovascular disease. DHA is also involved in the development of the eyes and brains of young infants.
Recommended Intakes for Dietary Fats
The National Academies of Science, Engineering, and Medicine recommends that adults consume 20–35% of total calories from dietary fats. For a 2,000-calorie daily diet, that’s between 400 and 700 calories from fat, or about 44 to 78 grams. In addition, the World Health Organization and the U.S. Dietary Guidelines recommend that less than 10% of daily calories come from saturated fats, and that trans fat consumption be kept as low as possible. While there are no formal recommendations for PUFA or MUFA intake, the guidelines for saturated and trans fats imply that most of our dietary fat intake should come from unsaturated fats.
Tips for Making Healthy Choices Around Dietary Fats
- Cook with and eat foods and beverages with higher amounts of PUFAs and MUFAs. For example, choose olive, canola, or soybean oil for cooking instead of coconut or palm oils. Or swap in avocado, nuts, or seeds for high-fat meats and cheeses.
- Read food labels to help you choose foods and beverages lower in saturated fat.
- Pay attention to portion sizes for foods higher in saturated fat. Consider opting for a smaller portion of high-saturated fat foods, or eat these foods less often.
This article includes contributions from Kris Sollid, RD; Ali Webster, PhD, RD; and Marisa Paipongna.