Fats: The Good, The Bad, and The Ugly

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Fats are confusing. There are some good ones, a lot of bad ones, and it is hard to keep track of the ones you want and the ones you don’t. Hopefully, this article will help keep things straight.

The body contains three types of lipids. Lipids are a class of organic compounds that are insoluble in water. One of the least talked about but most important types of lipids in the body are phospholipids. Phospholipids are the main constituent of cell membranes and play an important role in determining what enters the cell and what is left out.

The second type of lipids are called sterols. Cholesterol is a sterol and is used by the body in the synthesis of hormones. Cholesterol is, of course, infamous for its links to cardiovascular disease. However, there are two types of cholesterol – “good” cholesterol and “bad” cholesterol. This classification is based on the type of lipoproteins in which the cholesterol is contained. Lipoproteins are essentially large droplets of fats. The core of lipoproteins is composed of a mix of triglycerides and cholesterol and this core is enclosed in a layer of phospholipids. There are five different types of lipoproteins, but the two types that are most known are low density lipoproteins (LDL) or “bad cholesterol” and high-density lipoproteins (HDL) or “good cholesterol.”

Bad cholesterol, in high quantities, accumulates in the walls of arteries, where LDLs are oxidized.           Oxidized LDL causes damage to the walls of arteries. This damage leads to inflammation which leads to a constriction of arteries (leading to high blood pressure) and to further accumulation of cholesterol, leading to the formation of plaques. These plaques further narrow arteries, decreasing the flow of blood and oxygen to tissues.

High density lipoproteins, or good cholesterol, on the other hand plays an important role in reverse cholesterol transport, a process by which excess bad cholesterol is transported to the liver for disposal. Good cholesterol also has anti-inflammatory and vasodilatory properties and protects the body from LDL-oxidative damage.

Perhaps unsurprisingly, fried food, fast food, processed meats, and sugary desserts lead to increased bad cholesterol levels while fish, nuts, flax seeds and – you guessed it! – avocados lead to increases in good cholesterol levels.

The final type of lipids in the body are triglycerides. Triglycerides are the fat in the blood. Any calories that are not utilized by the body are stored in the form of triglycerides. The effect of high levels of triglycerides on the heart have not been as well understood. Excessive triglyceride levels are typically accompanied by high (bad) cholesterol levels and research in the past couple of years has indicated a relationship between high triglyceride and risk for cardiovascular disease.

The fats that we consume, however, are not in the form of triglycerides. The fats that we consume are broken down and converted into triglycerides and cholesterol. The major dietary fats are classified into saturated fats, trans fats, monounsaturated fats, and polyunsaturated fats.

Saturated fats are fats whose molecules have no carbon-carbon double bonds. Saturated fats are fats to be avoided because they increase LDL levels by inhibiting LDL receptors and enhancing lipoprotein production. Saturated fats are solids at room temperature and are found in fatty beef, lamb, pork, butter, lard, cream, and cheese.

Trans fats are also bad fats. They are typically found in margarine, baked items, and fried food. They suppress chemicals that protect against the build up of plaques in artery walls, increase bad cholesterol and decrease good cholesterol.

Monounsaturated fats and polyunsaturated fats are fats that have one (mono) and many (poly) carbon-carbon double bonds in their molecules respectively. These fats are liquids at room temperature and are found in salmon, nuts, seeds, and vegetable oils. Polyunsaturated fats are associated with decreased bad cholesterol and triglyceride levels.

Keeping track of which fats are found in which food can seem intimidating, but foods that lead to increased good cholesterol levels are foods that are typically considered healthy – nuts, seeds, fish, fruits, and vegetables, while foods that lead to excessive bad cholesterol are foods that we are taught to avoid in excess anyway – such as processed and fatty meats, processed food, and fried food.

Resources:
Contains both information on what various types of fats are and also food that contains the respective fats: https://www.hsph.harvard.edu/nutritionsource/what-should-you-eat/fats-and-cholesterol/types-of-fat/
A guide to choosing healthy fats: https://www.helpguide.org/articles/healthy-eating/choosing-healthy-fats.htm
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5577766/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5586853/