16.5 The Basics of Fat

Fat is Essential

Some people attempt to eliminate fat from their diets, while others try to consume a high-fat diet. What is ideal? Fat is an essential nutrient that the body needs to survive and function properly, and it can’t produce it in adequate amounts, so we need to consume fat (Institute of Medicine, Food and Nutrition Board, 2005). The fats we consume are known as dietary fats.

In addition to helping us feel satiated, fats—also known as lipids—fulfill many critical functions in the body. For example, cholesterol, a type of lipid, maintains membrane fluidity; it is part of every cell in the body, a major component of the brain and nerves, and is necessary for the body to produce vitamin D, bile acids, and many hormones, including estrogen and testosterone. Additionally, lipids regulate cell permeability and cell metabolism, act as signaling molecules and as electrical insulators to nerve fibers, and participate in some enzyme systems.

Fat serves as a source of and is necessary for the proper absorption and function of the essential fat-soluble vitamins: A, D, E, and K. Further, fat stored in our bodies helps cushion organs against shock, provide insulation, and regulate body temperature, in addition to serving as a reserve of energy in the form of triglycerides.

All fats are made up of fatty acids and glycerol, fatty acids being the major component. The human body can manufacture most of the fat it needs, including cholesterol, but it cannot make the essential fatty acids, or at least not enough of them, so we need to consume those (Institute of Medicine, Food and Nutrition Board, 2005). Linoleic acid, an omega-6 fatty acid, is required for growth, skin maintenance, and normal functioning of the reproductive system. Alpha-linolenic acid, eicosapentaenoic acid—or EPA—and docosahexaenoic acid—or DHA—are omega-3 fatty acids. The omega-3s are an integral part of all cell walls throughout the entire body, but found in high amounts in the brain and eyes. DHA is necessary for proper neuronal function. Omega-3 deficiency can alter the structure and function of brain cell membranes and prevent the renewal of membranes, affecting brain development, accelerating cerebral aging, decreasing the perception of pleasure, and likely affecting cognitive performance (Bourre, 2004; Bourre, 2005; Muldoon, Ryan, Yao, Conklin, & Manuck, 2014).

For these reasons, consuming fat is essential.

The Type of Fat We Consume Matters

Dietary fats are classified as unsaturated, saturated, or trans. Most foods provide a mixture of these in varying amounts.

Unsaturated Fats

Unsaturated fats are generally liquid at room temperature and found primarily in fish and other seafood, nuts, seeds, and oils from seeds and vegetables. Types of unsaturated fats include monounsaturated and polyunsaturated.

Concentrated sources of monounsaturated fats include:

• Avocados
• Nuts
• Seeds
• Olives
• Canola, olive, avocado, and peanut oils

Polyunsaturated fats include the essential omega-3 and omega-6 fatty acids; the most highly concentrated sources are:

• Fish and seafood, especially fish eggs and fatty fish from cold water sources
• Walnuts
• Flax, hemp, and chia seeds
• Canola, sunflower, corn, soybean, flaxseed, and hemp seed oils

Legumes, grains, fruits, vegetables—including sea vegetables—and microalgae, such as spirulina, are low in fat overall, but the fat they provide is largely polyunsaturated.

While unsaturated fats make up a relatively small portion of the fat in most animal-based foods, eggs are an exception; most of the fat in eggs is unsaturated (Egg Nutrition Center, n. d.).

Because of the importance of omega-3 fatty acids and their limited sources, many food products are enriched with them.

Saturated Fats

Saturated fats are generally solid at room temperature and found mainly in animal-based foods, such as beef, pork, bacon, sausage, milk, cheese, and butter. Plant-based sources of saturated fat include coconut and palm oils.

Pizza, cookies and other desserts, and mixed food dishes are other common sources of saturated fat (National Cancer Institute Division of Cancer Control and Population Sciences, 2018).

Trans Fat

Trans fats are naturally present in small amounts in meat and dairy products and in very small amounts in vegetable oils.

Other trans fats available in our food supply are artificially made through a process called hydrogenation, which in essence saturates unsaturated fats, making them solid at room temperature; these are called hydrogenated or partially hydrogenated oils—or PHOs (U.S. Food and Drug Administration, U. S. Department of Health, 2018). Shortening is one example of a PHO. Food manufacturers like PHOs because they make food products more shelf-stable and can reduce manufacturing costs. PHOs have been commonly used in processed foods like crackers, cookies, and other packaged baked goods, as well as fried foods. However, due to extensive research demonstrating negative health effects of trans fat and pressure from consumers, consumer advocacy groups, and public health organizations, in 2015 the United States Food and Drug Administration or FDA declared that PHOs are not considered safe, and, as of June 2018, United States manufacturers can no longer add PHOs to food products (U.S. Department of Health and Human Services, 2015; U.S. Food and Drug Administration, 2015). Those produced before June 2018 were allowed for distribution through January, 2020, and an extension to January 2021 was granted for some limited uses of PHOs (U.S. Food and Drug Administration, U. S. Department of Health and Human Services, 2018).

Benefits of Unsaturated Fats Over Saturated and Trans Fats

The different types of dietary fats affect blood lipids in different ways. LDL cholesterol is considered bad cholesterol—think L for lousy or low; having high LDL cholesterol is associated with increased risk of cardiovascular disease, so we want it to be low. HDL cholesterol is considered good cholesterol—think H for healthy or high; having high HDL cholesterol is associated with decreased risk of cardiovascular disease, so we want it to be high.

Trans fats increase disease risk. They raise LDL cholesterol and lower HDL cholesterol, thus contributing to increased risk of cardiovascular disease. They also contribute to insulin resistance and create inflammation, which is associated with cardiovascular disease, stroke, diabetes, and other chronic diseases (Risérus, Willett, & Hu, 2009; Mozaffarian et al., 2004).

High saturated fat intake has long been associated with increased LDL cholesterol and risk of cardiovascular disease (Sun et al., 2015). Although some recent research appears to indicate that saturated fats may not be as harmful as previously thought, a plethora of scientific evidence clearly demonstrates that minimizing intake of saturated fats decreases cardiovascular disease risk, as long as they’re replaced with unsaturated fats or complex carbohydrates instead of trans fats, refined grains, and simple or added sugars (Nettleton, Brouwer, Mensink, Kiekman, & Hornstra, 2018; Sacks et al., 2017; Hooper et al., 2013; Hooper, Martin, Abdelhamid, & Davey Smith, 2015; Mozaffarian, Micha, & Wallace, 2010; Li et al., 2015).

Unsaturated fats are the healthiest type of fat. They lower LDL cholesterol and triglycerides, increase HDL cholesterol, and positively influence a variety of other cardiovascular risk factors, thereby reducing the risk of cardiovascular disease (Wang & Hu, 2017; Maki, Eren, Cassens, Dicklin, & Davidson, 2018; Colussi, Catena, Novello, Bertin, & Sechi, 2017; Leaf, 2007). Unsaturated fats also help improve glucose metabolism and prevent insulin resistance (Riserus et al., 2009, Maki, et al., & 2018; Colussi et al., 2017). Omega-3 polyunsaturated fats reduce inflammation and oxidative stress and may be helpful in the treatment of rheumatoid arthritis and other chronic inflammatory conditions (Colussi et al., 2017; Yates, Calder, & Rainger, 2015). Further, the omega-3s play a role in the prevention of depression and dementia, particularly Alzheimer’s disease, and appear effective in the prevention of stress as well (Bourre, 2005; Bourre, 2006b). Fish is a rich source of omega-3 fatty acids, and consuming one to four servings per week has been shown to have a significantly beneficial effect on the prevention of cardiovascular disease (Zheng et al., 2012).

Therefore, it’s healthiest to focus on getting the fat the body needs mostly from sources of unsaturated fats, while minimizing intake of saturated and trans fats. In particular, it’s recommended to eat at least one source of omega-3 fatty acids each day, and at least one serving of fish each week (Harvard T. H. Chan School of Public Health, 2015b).