What is lipid metabolism?

Lipid metabolism is the process by which fatty acids are digested, broken down for energy, or stored in the human body for later use. These fatty acids are a component of triglycerides, which make up most of the fat that humans eat in foods such as vegetable oils and animal products. Triglycerides can be found in blood vessels and stored for future energy needs in adipose tissue cells, better known as body fat, and liver cells. Although the body's main source of energy is carbohydrates, when this source is depleted, the fatty acids in triglycerides are broken down as a backup energy source. Examples of times the body draws energy from lipid metabolism are during exercise, when the supply of glycogen or the stored form of carbohydrate glucose is depleted, or when there are not enough carbohydrates in the diet to meet energy needs. of the body.

Triglycerides, also known as lipids or fats, are well suited to their role as a form of stored energy, as each gram supplies 9 calories (37 kilojoules), while carbohydrates supply only 4 calories (17 kilojoules) per gram. Since calories are units of energy, fats are considered nutritional nutrients. Triglycerides are made up of three chains of fatty acids linked to a hydrogen-containing compound called glycerol, fatty acids that can be released during lipid metabolism when the body needs these calories for energy.

The first step in lipid metabolism is the consumption and digestion of triglycerides, which are found both in plant foods such as olives, nuts, and avocados, and in animal foods such as meats, eggs, and dairy products. These fats travel through the digestive tract to the intestine, where they cannot be absorbed as triglycerides. Instead, they are broken down through an enzyme called lipase into fatty acids and most often a monoglyceride, which is a single fatty acid chain attached to a glycerol. These split triglycerides can be absorbed through the intestines and reassembled into their original form before being transported by chylomicrons, a type of cholesterol-like substance known as a lipoprotein, to the lymphatic system.

From the lymphatic system, triglycerides enter the bloodstream, where the process of lipid metabolism can be completed in one of three ways, as they are transported to the liver, muscle cells, or fat cells, where they are stored or used. for energy. If they end up in liver cells, they are converted to a type of "bad" cholesterol known as very low-density lipoprotein (VLDL) and released into the bloodstream, where they work to transport other lipids. Triglycerides delivered to muscle cells can be oxidized in the mitochondria of those cells for energy, while those delivered to fat cells will be stored until needed for energy at a later time. This results in an increase in the size of fat cells, visible in a person as an increase in body fat.

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