Lipid Metabolism

lipid metabolism

Core Concepts

In this article you will be able to fully understand the fascinating procoess of lipid metabolism. At the end of this article you will also know and comprehend all the metabolic pathways that lipids go through!

Related Topics

Lipid Metabolism

Lipid metabolism is the production and destruction of lipids in cells. It involves the breakdown and storage of fats for energy as well as the synthesis of structural and functional lipids, such as those necessary for the creation of cell membranes.

Since cells can transform glucose products into lipids, lipid metabolism actively links to carbohydrate metabolism.

Types of Lipids

Membrane Lipid

  • Phospholipids: component of the lipid-bilayer of the cell membrane.
  • Sphingolipids: found in cell membrane of neural tissue.
  • Glycolipids: maintains stability and cell recognition.
  • Glycerophospholipids: also found in neural tissue.

Other types of Lipids

  • Cholesterols: controls cell membrane fluidity.
  • Steroids: important for cell signaling molecules.
  • Triacyglycerols: major form of energy storage in the body.
  • Fatty acids: used for energy.
  • Eicosanoids: made from fatty acids and used for cell signaling.
  • Ketone bodies: made from fatty acids in the liver, and produce energy on periods of low food intake.

Lipid Digestion and Absorption

The first step of the metabolism is digestion. In this step, lipase helps break down triglycerides into smaller units called monoglycerides. It all begins in the mouth; the chemical digestion starts with the lingual lipase, then lipids go down to the stomach and the digestion continues with the gastric lipase. In this step it is also starting the mechanical digestion, called peristalsis. On the small intestine, pancreatic lipase and bile salt-depending lipase help to breakdown the molecules. Finally, individual fatty acid molecules are absorbed into the small intestine cells.

Lipid Transportation and Storage

Within the intestinal cells, phospholipid vesicles known as chylomicrons actively pack these triglycerides with cholesterol molecules. The movement of lipids and cholesterol by chylomicrons facilitates the creation of watery environments in the lymphatic and circulatory systems. Chylomicrons exit the enterocytes through exocytosis and enter the lymphatic system through the lacteals in the intestinal villi. The lymphatic system delivers the chylomicrons to the circulatory system. Once in circulation, they can either be stored in adipocytes, the fat cells that compose adipose tissue throughout the body, or transported to the liver.

Lipids require special transport proteins, lipoproteins, this due to their natural hydrophobicity. The liver synthesizes most of these lipoproteins. White adipose tissue stores lipids in the form of triglycerides. These molecules form from a backbone of glycerol with 3 fatty acids.


In order to convert triglycerides into energy, the body actively hydrolyzes them, separating them into their two main components, fatty acids and glycerol. In the cytoplasm, a process known as lipolysis takes place. The body actively converts the resultant fatty acids into acetyl CoA through β-oxidation, which the Krebs cycle utilizes. After undergoing lipolysis, the liberated glycerol from triglycerides actively enters the glycolysis pathway as DHAP. Fat molecules provide more energy than carbohydrates and are a significant source of energy for the human body because one triglyceride molecule creates three fatty acid molecules, each of which can contain up to 16 carbons.

Comparing triglycerides to proteins and carbs, they provide more than twice as much energy per unit mass. When glucose levels are low, the body actively transforms triglycerides into acetyl CoA molecules and utilizes them to produce ATP through aerobic respiration.

The cytoplasm actively transforms fatty acids into fatty acyl CoA molecules, initiating the process of fatty acid oxidation, also known as β-oxidation.To assist move the fatty acid across the mitochondrial membrane, this fatty acyl CoA joins with carnitine to form a fatty acyl carnitine molecule. After entering the mitochondrial matrix, the body actively converts the fatty acyl carnitine molecule back into fatty acyl CoA and subsequently into acetyl CoA.

The newly produced acetyl CoA enters the Krebs cycle and is utilized to make ATP.



If the oxidation of fatty acids produces an excess of acetyl CoA and overwhelms the Krebs Cycle, the body actively redirects acetyl CoA to produce ketone bodies. When a person experiences chronic malnutrition or uncontrolled diabetes, and is unable to utilize a significant amount of blood glucose, the body actively utilizes ketones as a source of fuel. In both situations, the body releases fat reserves to generate energy through the Krebs cycle, resulting in the production of ketone bodies when there is an excessive accumulation of acetyl CoA.


Ketone Body Oxidation

Ketones are a different energy source that may be used by organs, including the brain. This prevents the brain from shutting down when glucose is scarce. When the production of ketones surpasses their rate of utilization, they can actively convert into CO2 and acetone. The body eliminates acetone by exhaling it. One sign of ketogenesis is a sweet, alcoholic aftertaste on the patient’s breath. One approach to determine if a diabetic is effectively managing their condition is by this impact. A hazardous disease for diabetics, diabetic ketoacidosis, can result from the carbon dioxide created when the blood becomes acidic.


When glucose levels are abundant, the body actively transforms the excess acetyl CoA produced by glycolysis into fatty acids, triglycerides, cholesterol, steroids, and bile salts. In the cytoplasm of adipocytes (fat cells) and hepatocytes (liver cells), a process known as lipogenesis converts acetyl CoA into lipids (fat). Your body utilizes acetyl CoA to convert extra glucose or carbs into fat when you consume more than what your body requires. Acetyl CoA can come from a number of metabolic processes, although glycolysis is where it is most frequently produced. Due to the fact that it starts lipogenesis, acetyl CoA availability is important.

Acetyl CoA serves as the starting point for lipogenesis, which then progresses by adding two carbon atoms from another acetyl CoA. The process continues until the fatty acids reach the desired length, actively utilizing ATP as an anabolic mechanism to form bonds. Triglycerides and lipids are actively produced to efficiently store the energy contained in carbohydrates. Adipose tissue reserves high-energy molecules known as lipids and triglycerides.

Lipid Metabolism Practice Problems

Problem 1

Why is the lipid metabolism actively links to the carbohydrate metabolism?

Problem 2

Name the 4 steps of the lipid metabolism

Problem 3

Adipose tissue reserves what type of molecules?

Problem 4

What does the body uses as fuel when a person experiences chronic malnutrition or uncontrolled diabetes?

Problem 5

Where does the newly formed acetyl CoA molecules, from liploysis, enter?

Lipids Metabolism Practice Problem Solutions

Problem 1

Because cells can transform glucose products into lipids

Problem 2

Digestion, absorption, transformation and storage

Problem 3

Lipids and triglycerides

Problem 4


Problem 5

To the Krebs Cycle

Further Reading

If you liked the topic, and everything about metabolism, we invite you to check these academical articles!