Dietary Fats: Basics
What are dietary fats?
Dietary fats are a type of nutrient and a source of food energy (calories).
Fats consist of a wide group of compounds. The body breaks these down into fatty acids.
Fatty acids are simple molecules made up of carbon atoms bonded with hydrogen atoms. They are part of a class of compounds known as carboxylic acids. These types of fatty acids are characterized by the number of carbon atoms with or without hydrogen atoms bonded to them and the length of the carbon chain.
A lipid (fat) is an organic compound that is insoluble in water, but soluble in organic solvents. Organic solvents are chemical class of volatile carbon-based compounds capable of dissolving other chemicals. Common organic solvents include alcohols, esters, ethers, ketones, amines, and aromatic compounds such as benzene.
Why are dietary fats important?
Dietary fats are more energy dense than carbohydrates, and contain twice as many calories. Not only do they provide energy, but they help cushion and insulate organs, protect cells by acting as a major component in cell membranes, maintain skin and hair, send signals in the form of hormones, and are necessary for the production and absorption of certain vitamins and hormones. Fatty acids play an important role in brain development, blood clotting and inflammatory control, among other actions.
What are the different types of fats?
The most abundant of dietary lipids are triglycerides (also known as triacylglycerols), which is an ester derived from three fatty acids linked to the alcohol glycerol.
Fat molecules are also classified as monoglycerides and diglycerides depending on how many fatty acid chains are present.
The carbon chain length of the fatty acids determines whether it is classified as a short-chain, medium-chain, or long-chain fatty acid. Short-chain fatty acids have less than eight carbons, medium-chain acids have eight to fourteen carbons and long-chain fatty acids have 16 or more carbons.
“Most biological fatty acids contain an even number of carbon atoms because the biosynthetic pathway common to all organisms involves chemically linking two-carbon units together (although relatively small amounts of odd-number fatty acids do occur in some organisms” (1).
However, essential fatty acids (fatty acids that the body needs and cannot synthesize on its own or derive from other fatty acids) from a nutritional perspective are considered short-chain if they have 18 carbons and long chain if they have 20 or more carbons (2).
There are three main types of fats: saturated fats, unsaturated fats, and trans fats. Unsaturated fats are further classified as monounsaturated and polyunsaturated.
Saturated fats
Saturated fats are molecules that are saturated with hydrogen atoms. The molecules form regular shapes that clump together easily. Consequently, they are more likely to stick to the sides of arteries. They can build up and cause the arteries to clog, raising blood pressure.
They are generally solid at room temperature and are commonly found in animal food sources, such as beef, lamb, pork, poultry, butter and cheese. They can also be found in palm oil, and in fast foods and processed or commercial products such as pastries.
While increased consumption of saturated fats has been linked with heart disease, it can still be consumed in small amounts, such as those found in some vegetable sources.
Saturated fatty acids have the maximum possible number of hydrogen atoms bonded to each carbon in the molecule. They are “saturated” with hydrogen atoms. This saturation makes the fatty acid stable, which means it can withstand more heat. Saturated fats are solid at room temperature.
Unsaturated fats
Unsaturated fats include monounsaturated and polyunsaturated fats. As the name implies, unsaturated fats are those that are not saturated with hydrogen. The molecules form irregular shapes that cannot clump together as easily. They are usually liquid at room temperature.
Monounsaturated and polyunsaturated possess different chemical structures and provide slightly different health benefits.
Monounsaturated fats
Monounsaturated fats are found in a variety of foods and oils. They are liquid at room temperature, but start to solidify when chilled. Sources of monounsaturated fats include canola and olive oil and avocados. These fats have been shown to reduce bad cholesterol levels and may help control blood sugar levels. They also help develop and maintain body cells as well as contribute vitamin E.
In a monounsaturated fatty acid, a hydrogen bond is missing, and instead one pair of carbon atoms forms a bond with each other (known as carbon-carbon double bonds). They are less stable than saturated fat, and are liquid at room temperature, though they solidify in cold temperatures, such as in the refrigerator.
Polyunsaturated fats
Polyunsaturated fatty acids are missing more than one pair of hydrogen atoms and have two or more carbon pairs bonded together instead.
Polyunsaturated fats are found mostly in plant-based foods and oils, and can be divided into two main groups: omega-3 fatty acids and omega-6 fatty acids.
Omega-3 fatty acids
Omega-3 fats possess a number of health benefits. They have been shown to lower LDL or “bad” cholesterol levels, lower blood pressure, lower triglycerides (fats in the blood), improve cognitive function, and help protect against various diseases. They can be found in fish and plant sources such as flaxseed, soybeans, and walnuts.
Omega-6 fatty acids
Omega-6 fatty acids also play a crucial role in brain function and help stimulate skin and hair growth, maintain bone health, and regulate the metabolism. They mainly come as linoleic acid from plant oils such as soybean oil, as well as from nuts and seeds.
Trans fats
Trans fats, also known as hydrogenated fats, are vegetable fats that have been treated with extra hydrogen in a process called hydrogenation. It turns oil into solid or semi-solid forms at room temperature, such as seen in margarine.
Hydrogenation is a process that involves adding hydrogen back into unsaturated fats. This changes the structure of the fat, making it stick in the lining of cells. It can then be attacked by free radicals which damage the rest of the lining of the cell (3).
A small amount of trans fats sometimes can be found in meat and dairy, but it is not usually found in nature and is instead artificially created.
These types of fats should be avoided. They are known as “bad fats” since they raise levels of LDL, or “bad” cholesterol, while lowering levels of HDL, or “good” cholesterol.
Sources include doughnuts, pies, pastries, biscuits, and other baked or fried foods.
How are fats digested by the body?
Because lipids are hydrophobic (water fearing), they are poorly soluble in the aqueous (water-based) environment of the digestive tract and tend to clump together and form large droplets, or fat globules.
When we eat, the mechanical process of chewing helps break down the food into smaller pieces. Then, the digestive enzyme lingual lipase acts as a catalyst for the hydrolysis reaction that helps break down triglycerides into diglycerides and free fatty acids. The process of breaking down the fat globules into smaller fat droplets is known as emulsification.
In the small intestine, these fat droplets are mixed with bile, a yellow, brown, or green fluid that is stored in the gallbladder and secreted by the liver to aid in digestion.
Bile acids act as a detergent on particles of fat and cause it to break down (emulsify) into microscopic droplets. It also acts as a lipid carrier by forming micelles. Bile molecules have hydrophobic and hydrophilic (water loving) regions. “The hydrophobic end sticks to each fat molecule and the hydrophilic protrudes to prevent the molecules from sticking together” (4). The combined structure is known as a micelle. Micelles also contain fat soluble vitamins and cholesterol.
The finer droplets of fat have more surface for the action of the enzyme pancreatic lipase. The lipase further breaks down the fat into free fatty acids and monoglycerides.
Free fatty acids, monoglycerides and some diglycerides can then be absorbed by the duodenum (the first part of the small intestine immediately beyond the stomach). As they pass through the small intestine, the fatty acids are reassembled into triacylglycerols inside the intestinal cells.
When joined with a protein carrier, triacylglycerols, cholesterol, and phospholipids form chylomicrons, a type of lipoprotein. “The lipoprotein particle is composed of an outer shell of phospholipid, which renders the particle soluble in water; a core of [lipids], including cholesterol and a surface apoprotein molecule that allows tissues to recognize and take up the particle” (5).
Lipoproteins allow the fat to move through the water inside and outside cells; and transport the food fat through the body to specific destinations such as the liver, kidney, adipose tissue and other tissues.
What makes some fats better than others?
What plays a significant role in the digestion and health effects of the fat is its source.
Short chain fatty acids transport through the bloodstream more easily and are quickly burned as fuel. Medium chain fatty acids readily form triglycerides stored inside fat cells. Long chain fatty acids are not as easy for the body to burn or store.
Saturated fats are considered unhealthy or “bad fats” because they tend to be hard to burn and store due to their structure, so the body usually uses them to make cholesterol. They can also promote the formation of fatty deposits that clog arteries.
These types of fats are mainly found in animal foods, though they are also in coconut oil. However, the type of fatty acid found in coconut oil, lauric acid, is a medium-chain triglyceride and is more easily absorbed and used in the body, where it is converted into a monoglyceride compound that exhibits antiviral, antimicrobial, and antifungal properties.
Unsaturated fats, particularly polyunsaturated fats that contain Omega-6 and Omega-3 fatty acids, are considered healthy fats because they promote HDL or “good” cholesterol. They also help reduce inflammation and promote heart health and proper functioning of other organs and tissues in the body. They are predominantly found in plant-based foods.
The worst type of fat is trans fats. The process of hydrogenation increases the shelf life and flavor stability of foods, but consumption of it is known to increase blood levels of LDL or “bad” cholesterol; lower levels of HDL cholesterol; increase the formation of fatty deposits, leading to clogging of the arteries and heart disease; and play a role in the development of type 2 diabetes and other health problems.
Too much fat, mainly saturated fats and trans fats found in animal foods and processed and refined foods, have been shown to increase LDL cholesterol and increase the risk of weight gain, heart disease, and cancer. It is recommended to limit or eliminate consumption of processed, refined, and animal based foods and increase consumption of fats found in plant-based foods, such as nuts and seeds (after proper preparation which includes the process of soaking them to remove enzyme inhibitors; Soaking Nuts, Seeds, Legumes, and Grains), avocados, and coconut oil. Some seafood, such as salmon, were also a good source of unsaturated fats. However, recent contamination from pollution and radiation have made most fish unsafe to eat.
Takeaway
Just as in the case of body fat and cholesterol, dietary fat is essential for the proper function and growth of the body. It is important to get a balance of the right kinds of fat, since too much of the “bad” kind can cause a rise in cholesterol and the buildup of fat in the body and can lead to a number of health complications and diseases. Since fat is more energy dense than carbohydrates and protein, less of it is needed to get what we need.
We live in a world that relies on fast and processed foods. Everywhere you look, people and animals alike are filling themselves with saturated and trans fats, and it shows with the increasing rate of obesity and disease.
Nevertheless, fat is not the enemy. It is an integral, irreplaceable part of the human body. By understanding how all types of fat works in the body, including dietary fat, body fat and fat-like substance cholesterol, we can learn to respect fat instead of fearing it or being addicted to it. We can apply what we know to create a diet and lifestyle that promotes the consumption of the fats we need to create a healthy body, and mind.