The terms cholesterol, triglycerides, and fat all evoke negative thoughts in us. However, the simple truth is that we cannot do without either cholesterol or triglycerides. Both are a shade different, but both are related to fats. Triglycerides are an energy resource/stored fat that replenishes at the time of need while cholesterol is responsible for the growth of cells and the issue of hormones. But too much of anything is bad and overproduction of cholesterol can lead to a hyper cholesterol stage, which eventually causes heart attacks.
In general, “fat” refers to triglycerides (fatty acid chains + glycerol), but “fat” could also refer to individual fatty acids. Fatty acids are a group of molecules that differ in the length of the hydrocarbon chain and the presence/absence and position of double bonds. Cholesterol, on the other hand, is a single molecule with a very different chemical structure from the fatty acids. Fats are either fatty acids or fatty acid derivatives, like triglycerides, and are characterized by long hydrocarbon chains which give them their hydrophobic quality, and a polar carboxylic acid “head” group which can react to form esters (like with glycerol) and other structures. The biological functions of cholesterol and fats are also different. Fats are primarily used for energy storage and metabolism. When you eat more calories than you need, fats are efficient molecules for storing this excess energy for the future. Fats are broken down and energy is released when our bodies need more power, although our bodies preferentially burn carbohydrates for energy before dipping into our fat stores. Fatty acids do play many other roles in biology, but fats and oils (usually) specifically refer to glycerol esters of fatty acids, which are basically fatty acids linked to glycerol. The main role of fats and oils is in energy metabolism and nutrition.
Cholesterol has many different biological roles. It is a component of cell membranes, where it gives them increased rigidity. In other words, cholesterol helps maintain the shape of the cell membrane, making it less flexible. Organisms that live in very high temperatures often have more cholesterol and similar molecules in their cell membranes, to prevent them from melting and spilling open the contents of the cell. Cholesterol is also part of bile, where it aids in the breakdown of fats, and is a precursor to many important biological molecules like vitamin D and testosterone.
Triglycerides are the main form of fat in our bodies and in our diets. They provide us with energy and insulation and protect our internal organs from damage. They also enable our bodies to metabolize proteins and carbohydrates more efficiently. Despite the many benefits triglycerides have, too much in our blood circulation can cause major health problems, such as heart disease. Knowing the right fats to eat can help reduce overall cholesterol levels and help us to maintain a healthy body. Triglycerides can be further divided into the following categories:
These are considered the most detrimental to your health. They usually are solid at room temperature and are derived from animal products. When looking at their molecular structure, saturated fats contain the maximum number of hydrogen atoms (hence “saturated” with hydrogen atoms). Eating a diet high in these has been strongly correlated to heart disease.
This type of lipid lowers “bad cholesterol” LDL, while leaving the “good cholesterol” HDL levels the same. Such fats are usually liquid at room temperature. When looking at their molecular structure, there are two hydrogen atoms missing with a double bond between two carbon atoms replacing them. Monounsaturated fats include canola oil and olive oil.
This type of fat tends to lower both LDL and HDL levels (remember–we want to keep high levels of HDL). These are liquid at room temperature and typically have more than two hydrogen atoms missing. Polyunsaturated fats include safflower oil, sunflower oil and corn oil.
Essential Fatty Acids
Essential fatty acids must be obtained through your diet in order to maintain the architecture of cell membranes. They are also used as a component in the production of eicosanoids, a type of hormone used by the body to help regulate blood pressure, blood clot formation, and immune function.
These include omega-6 and omega-3 fatty acids, which have been linked to lowering triglyceride levels. Common sources of essential fatty acids include vegetable oils, fish, grains, seeds, and vegetables. In addition, supplements of omega-6 and omega-3 fatty acids are available at pharmacies.
During hydrogenation, hydrogen atoms are added back to polyunsaturated or monounsaturated fats to protect against rancidity from bacteria or air exposure. As a consequence, this process causes hydrogenated fats to become saturated fats. If a food label states the words partially hydrogenated oils among its first ingredients, that means that it contains a lot of trans fats and saturated fats. These fats increase LDL levels and decrease HDL levels, which may increase your risk of heart disease. Such foods are best avoided, which goes to show it’s a good idea to always read food labels carefully.
TRIGLYCERIDES are neutral fat molecules made up of three fatty acids joined to one glycerol molecule through a special chemical linkage called an ester. Triglycerides are the basic chemical form of fat. Chemically, the structure of triglycerides is one molecule of glycerol (CHOH2-CHOH-CHOH2) attached to three fatty acids, such as oleic acid or linoleic acid. Triglycerides come from either ingestion of dietary fats or through the conversion of unused calories. Triglycerides are stored in the body’s fat cells until the body needs to metabolize them for energy.
Excessive triglyceride levels, or hypertriglyceridemia, can contribute to coronary artery disease. Higher levels of triglycerides can indicate poorly controlled type 2 diabetes, hypothyroidism, liver disease, or kidney disease. At normal levels, triglycerides are important in the production of energy for most cells in the body, except brain cells, and can be broken down to help build other cells.
CHOLESTEROL is something your body needs. Yes, it looks like wax and it looks like fat, but it is important for the production of estrogen in women, testosterone in men, and processing vitamin D in both sexes. Many cells use cholesterol as insulation to keep a cell fluid and functioning in cold temperatures. Cholesterol is a sterol (a combination steroid and alcohol) lipid found in the cell membranes of all tissues, and it is transported in the blood plasma of all humans. It is the protein content found in the cells of our body tissues and sets sail in our blood, although it doesn’t get dissolved in it per se. Cholesterol, with the chemical structure C27-H4-OH, acts as both a precursor for hormones and as a part of cellular membranes. The human body produces 2 grams of cholesterol per day, making up about 85 percent of blood cholesterol levels. The other 15 percent comes from a person’s diet. Most cholesterol from diet comes from oils and fats in foods. The body produces bile acids from cholesterol; bile acids break down oils and fats. The blood transports cholesterol via lipoproteins, which easily clump together with fats.
The two different types of lipoproteins are low-density lipoproteins (LDL) and high-density proteins (HDL). Lipoproteins carry cholesterol through the blood, and there are two kinds of lipoproteins. LDL, or low-density lipoproteins, is considered bad because a high level of LDL can cause heart disease. HDL, or high-density lipoproteins, is favorable when high.
Too much cholesterol can increase LDL production while decreasing HDL production. Excessive LDL builds up on arterial walls and hardens to create plaque, constricting flow and contributing to heart disease. On the other hand, HDL removes excess cholesterol from the body. When cholesterol clogs arteries, it is recognized as plaque. The narrowing of arteries caused by plaque may result in atherosclerosis. Consumption of saturated fats, trans fats (or trans fatty acids), and foods that contain hydrogenated oils may raise your LDL level. Foods such as certain meats, eggs and cheese are also high in cholesterol. Excess weight, a sedentary lifestyle, age, sex, and a family history of high cholesterol influence a person’s cholesterol level as well. While cholesterol and fatty acids are both transported by lipoproteins, because “lipid” is such a broad category of molecules, so is “lipoprotein.” Lipoproteins are proteins that transport lipids, but lipids are diverse and even the same lipid can have multiple functions, and different proteins may carry the same lipid to different parts of the body for different purposes.
For more detail, go to your biology textbook first. A general/introductory biology text may not have a lot of detail on cholesterol, but it should describe the general structure and function of fats (triglycerides) and fatty acids. The Wikipedia articles on lipid, fat, oil, cholesterol and lipoprotein also have more info, and a web search for these words will also provide a lot more information.
Take a look at these drawings of the molecular structure of cholesterol and myristic acid, a fatty acid:
Even if you are not familiar with the way that chemists represent molecules and exactly what these drawings mean, you can see that they are very different.
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