This is the first installment of a new video series in partnership with Osmosis, a group that focuses on health science education, highlighting the basics of several nutrition topics.
Fats are an essential part of a healthy diet. They’re involved in everything from providing a major source of energy, to helping absorb vitamins, to refereeing communication between the cells in our body. As if these health benefits weren’t enough, they also contribute to our enjoyment of food by adding taste and texture, like the smoothness of guacamole or the flakiness of a croissant. What a versatile nutrient!
To understand the foundation of dietary fats, let’s start with the basics. 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 it has three fatty acid chains, the whole thing is called a triglyceride. If there are only one or two fatty acid chains, it’s 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. There are short chain fatty acids that have 4 to 6 carbons, which can be found in dairy products and are also produced by our gut microbiome. Medium chain fatty acids, like myristic and lauric acids found in coconut oil, have 8 to 14 carbons. And long chain fatty acids like oleic acid in olive oil have more than 14 carbons.
Fatty acid chains are also categorized by whether they have single or double bonds connecting the carbons. When a fatty acid has only single bonds, it’s called a saturated fatty acid because it has as many hydrogen atoms as possible – it’s saturated with them! Triglycerides with saturated fatty acids are nice and straight so they pack together really well, and as a result they’re usually solid 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. Unsaturated fatty acids can be further classified according to the number and location of their double bonds. You can read all about unsaturated fats here.
Trans fatty acids are a type of unsaturated fatty acid that have hydrogen atoms on the opposite side of the double bond – kind of diagonal from each other. This is different from 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’re also created through the partial hydrogenation of liquid oils. Partially hydrogenated oils have been largely removed from foods in North America and Europe because trans fats have been associated with coronary heart disease.
Fats play very important roles throughout the body. For example, polyunsaturated fats (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. Omega-3 fatty acids like docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) help lower plasma triglyceride levels, which also protects against cardiovascular disease. DHA is also involved in development of the eyes and brains of young infants.
The impact of saturated fat on cardiovascular health is more complex. Generally speaking, it’s recommended to keep consumption of saturated fat low, but evidence suggests that different types of saturated fatty acids may have different effects on our cardiovascular health. The health impact of reducing or replacing saturated fat in the diet may also depend on the nutrient that replaces it. For example, replacing saturated fat with polyunsaturated fat has been shown to benefit cardiovascular health, but replacing saturated fat with refined carbohydrate has not.
The National Academies of Science, Engineering, and Medicine recommends consuming 20-35% of our daily calories as fats. For a 2000 calorie diet that’s between 400 and 700 calories from fat, or about 44 to 78 grams. The World Health Organization and the US Dietary Guidelines recommend that less than 10% of daily calories come from saturated fats and that trans fat consumption should be kept as low as possible.
This blog includes contributions from Allison Webster, PhD, RD.