Dietary fats can be a confusing topic, at least it was for me when I started learning more about what I was eating.
This is part one of two post related to dietary fats. In this post, I’ll cover the basics and how this translates into our day to day eating and health. In the second part, I’ll hone in specifically on a subset of cooking oils.
Fatty acids are the major form of dietary fat,
existing in triglyceride form in food, a glycerol back bone with three fatty acid chains.
It is the difference in their chain length and saturation status that determines their role in food and cooking, in addition to their impact on our health. In the last half of the 20th century, there was widespread recommendations to reduce total dietary fat intake in our eating, also known as the “low fat” diet.
Related to this recommendation was a trend that resulted in increased consumption of refined carbohydrates and added sugars and avoidance of foods rich in healthful fats (unsaturated fats). Evidence supports substituting unsaturated fats (polyunsaturated fats) in place of saturated fats as apart of a healthful eating pattern to reduce the risk of developing cardiovascular disease and other chronic illnesses.
such as the Institute of Medicine and the World Health Organization, recommend total fat intake between 20-35% of total calories. The 2015-2020 USDA Dietary Guidelines only make a recommendation to limit saturated fat to less than <10% of total caloric intake daily but does not specify a recommendation for total fat intake. There has been an increased support for a more holistic recommendation of shifting dietary recommendations to focus on healthful food based dietary patterns while limiting ultra-processed foods, refined carbohydrates, added sugars and excessive sodium intake. In addition, emphasis is placed on the quality of fat that is emphasized for consumption vs discrete amounts.
Dietary fatty acids are often classified according to their hydrocarbon chain length and their saturation status. The following will be a breakdown based on the saturation status of groups of fatty acids.
By now, I am sure we have all heard about the detrimental health effects due to the consumption of trans fats, specifically increasing the risk of developing cardiovascular disease by raising LDL, triglycerides, increasing inflammation and endothelial dysfunction.
There is no human benefit in the consumption of trans fat and according to the Institute of Medicine, there is no safe level of consumption for industrial trans fat. Industrial trans fat is formed through a manufacturing process that adds hydrogens to vegetable oil (i.e partially hydrogenated), effectively converting a liquid fat into a solid fat at room temperature. In addition, trans fat also occurs naturally in food products such as milk, butter, cheese, and meat. In 2015, the Food and Drug Administration banned industrial trans fats in processed foods in the United States. Of note, a product can claim “zero trans fat” if it has less than 0.5 grams of trans fat PER serving.
If you see the an ingredient listed as a partially hydrogenated oil, it is referring to trans fat.
Limiting dietary saturated fat has been an overall consistent recommendation from multiple organizations.
Saturated fatty acids are fully hydrogenated, solid at room temperature and the fatty acids in this group do not contain double bonds. Examples of saturated fatty acids include carprylic, capric, lauric, myristic, palmitic, and stearic acids. Common sources of saturated fat include red meat, whole fat dairy products, coconut oil, palm oil and ultra-processed foods. Increased consumption of saturated fat can increase LDL which is a risk factor for the development of cardiovascular disease.
In regard to unsaturated fats, there are two types, monounsaturated and polyunsaturated.
Polyunsaturated fatty acids (PUFAs) contain two or more double bonds and are generally liquid at room temperature. This group is further subdivided into two groups of essential fatty acids (i.e humans cannot produce these), omega-3 and omega-6. Omega-6 includes linoleic acid, most commonly found in soybean oil, safflower oil and corn oil and arachidonic acid (AA) most commonly found in meat, poultry and eggs. Omega-3 includes alpha-linolenic acid derived from plant sources (flax seeds, chia seeds, walnuts, canola oil), eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA) and docosahaxaenoic acid (DHA) found in fish and seafood.
Monounsaturated fatty acids (MUFAs) contain one double bond and are present in a wide variety of foods including vegetable, nut and seed oil as well as meat and dairy products. Oleic acid is one of the most abundant MUFAs found in food, present in higher amounts in olive oil, canola oil, avocados and almonds. Oleic acid is also present in beef tallow, lard, palm oil, soybean and corn oil. It is the most commonly consumed fatty acid in the American diet. There is a large body of evidence supporting MUFA (oleic acid) intake as a part of a healthful Mediterranean diet eating pattern
It is important to avoid trans fat and lower the intake of saturated while replacing it with unsaturated fats to decrease the risk of developing cardiovascular disease. These recommendations can be achieved by focusing on healthful eating patterns such as the Mediterranean, DASH and plant-based diets. Healthful fats have a role when eaten in the context of an overall healthy eating pattern.
Liu, A.G., Ford, N.A., Hu, F.B. et al. A healthy approach to dietary fats: understanding the science and taking action to reduce consumer confusion. Nutr J 16, 53 (2017). https://doi.org/10.1186/s12937-017-0271-4
Vannice G, Rasmussen H. Position of the academy of nutrition and dietetics: dietary fatty acids for healthy adults. J Acad Nutr Diet. 2014 Jan;114(1):136-53. doi: 10.1016/j.jand.2013.11.001. Erratum in: J Acad Nutr Diet. 2014 Apr;114(4):644. PMID: 24342605.