Lipid metabolism

Last updated date: 07-May-2023

Originally Written in English

Lipid Metabolism


Lipid metabolism is the production and degradation of lipids in cells, which includes the breakdown or storage of fats for energy as well as the creation of structural and functional lipids, such as those involved in cell membrane building. These fats are acquired from diet or produced by the liver in animals. Lipogenesis is the process through which these fats are synthesized.

The most of lipids found in the human body as a result of food consumption are triglycerides and cholesterol. Fatty acids and membrane lipids are two further forms of lipids present in the body. Lipid metabolism is frequently thought of as the digestion and absorption of dietary fat; however, organisms may receive energy from two sources of fat: ingested dietary fats and stored fat.

Both kinds of fat are used by vertebrates (including humans) to generate energy for organs such as the heart to operate. Because lipids are hydrophobic substances, they must be solubilized before they can be metabolized. Hydrolysis, which happens with the aid of numerous enzymes in the digestive system, is a common starting point for lipid metabolism.

 Plants also have lipid metabolism, albeit the mechanisms differ slightly from those seen in mammals. Following hydrolysis, the fatty acids are absorbed into the epithelial cells of the intestinal wall. Fatty acids are packed and distributed to the rest of the body via epithelial cells.


Lipid Metabolism Pathway

Lipid Metabolism Pathway

1. Lipid digestion:

The first stage in lipid metabolism is digestion, which is the act of breaking down triglycerides into smaller monoglyceride units with the aid of lipase enzymes. The chemical breakdown of lipids by lingual lipase begins in the mouth. Lipases do not break down ingested cholesterol, therefore it remains intact until it penetrates the epithelial cells of the small intestine.

Lipids are subsequently transported to the stomach, where chemical digestion is carried out by gastric lipase and mechanical digestion commences (peristalsis). However, the bulk of lipid digestion and absorption takes place after the fats enter the small intestine.

Chemicals from the pancreas (pancreatic lipase family and bile salt-dependent lipase) are secreted into the small intestines to aid in the breakdown of triglycerides, along with further mechanical digestion, until they are individual fatty acid units capable of being absorbed into the epithelial cells of the small intestine. The pancreatic lipase enzyme is in charge of signaling the breakdown of triglycerides into free fatty acids and glycerol units.


2. Lipid absorption:

Fat absorption is the second stage in lipid metabolism. Short chain fatty acids can be absorbed in the stomach, however the majority of fat absorption happens primarily in the small intestine. Triglycerides, along with cholesterol, aggregate form micelles after being broken down into individual fatty acids and glycerols.

Fatty acids and monoglycerides exit the micelles and spread over the membrane, where they enter the intestinal epithelial cells. Fatty acids and monoglycerides are recombined into triglycerides in the cytoplasm of epithelial cells. Triglycerides and cholesterol are bundled into larger particles termed chylomicrons in the cytoplasm of epithelial cells, which are amphipathic structures that transport digested lipids. Chylomicrons will move via the circulation and into the body's adipose and other tissues.


3. Lipid transportation:

Because membrane lipids, triglycerides, and cholesterols are hydrophobic, they require particular transport proteins known as lipoproteins. Lipoproteins' amphipathic shape allows triglycerides and cholesterol to be carried through the blood.

Chylomicrons are a kind of lipoprotein that transports digested lipids from the small intestine to the rest of the body. The different densities of lipoproteins are due to the different kinds of lipids they carry.

Very-low-density lipoproteins (VLDL) transport triglycerides created by our bodies, whereas low-density lipoproteins (LDL) transport cholesterol to our peripheral organs. Although the liver produces some of these lipoproteins, it does not produce all of them.


4. Lipid catabolism:

After passing through the tissues, chylomicrons (or other lipoproteins) are broken down by lipoprotein lipase on the luminal surface of endothelial cells in capillaries, releasing triglycerides. Before entering cells, triglycerides are broken down into fatty acids and glycerol, and the leftover cholesterol is transported through the blood to the liver. 


Types of lipids

Types of lipids

The types of lipids involved in lipid metabolism include:

  1. Phospholipids: Phospholipids are a major component of the lipid bilayer of the cell membrane and are found in many parts of the body.
  2. Sphingolipids: Sphingolipids are mostly found in the cell membrane of neural tissue.
  3. Glycolipids: The main role of glycolipids is to maintain lipid bilayer stability and facilitate cell recognition.
  4. Glycerophospholipids: Neural tissue (including the brain) contains high amounts of glycerophospholipids.
  5. Cholesterols: Cholesterols are the primary precursors for several hormones in our bodies, including progesterone and testosterone. Cholesterol's primary role is to regulate cell membrane fluidity.
  6. Steroid:  Steroids are one of the important cell signalling molecules.
  7. Triacylglycerols (fats): Triacylglycerides are the major form of energy storage in human body.
  8. Fatty acids: Fatty acids are one of the precursors used for lipid membrane and cholesterol biosynthesis. They are also used for energy.
  9. Bile salts: Bile salts are secreted from liver and they facilitate lipid digestion in the small intestine.
  10. Eicosanoids: Eicosanoids are made from fatty acids in the body and they are used for cell signaling.
  11. Ketone bodies: Ketone bodies are made from fatty acids in the liver. Their function is to produce energy during periods of starvation or low food intake.


Why You Should Avoid Bad Lipids?

Avoid Bad Lipids

Most people have greater amounts of "bad" LDL cholesterol when they consume saturated fats. Saturated fats appear to increase the production of LDL cholesterol in your body while decreasing the number of receptors that remove LDL cholesterol from your blood.

Trans fats are extremely uncommon in nature. The majority of trans fats are created by converting unsaturated oils to saturated fats. These synthetic fats appear to not only raise LDL cholesterol levels, but also to lower "good" HDL cholesterol levels in your body. As a result, the FDA has taken efforts to eliminate artificial trans fats from foods.

Atherosclerosis can be caused by high amounts of cholesterol in your system (the hardening and narrowing of arteries). When you have high LDL levels in your system, fat particles bind to the walls of your arteries and eventually form plaques that limit blood flow. This can result in coronary heart disease, which can lead to heart attacks and strokes.


What Foods Contain High Quantity of Lipids?

Foods High Quantity of Lipids

Lipids are found in a variety of meals, although some are worse than others. Avoiding saturated fats is a crucial step in maintaining your health.

  • Beef Fat:

Beef fat, commonly known as beef tallow, is mostly composed of saturated fats. Saturated fats account for about half of the lipids in beef fat. In fact, a single tablespoon (12 grams) contains more than 6 grams of saturated fat.

  • Heavy Cream:

When fresh milk is pasteurized, a significant amount of fat is removed and blended with heavy cream. Heavy cream is therefore a high-fat liquid. Even though it is liquid at room temperature, heavy cream includes a significant quantity of saturated fat.

  • Poultry Skin:

Chicken and turkey are both high in protein and low in fat. Their skin, on the other hand, is not. Poultry skin has a lot of lipids. Up to 2.26 grams of saturated fat may be found in one ounce of chicken skin.

  • Butter:

Condensing the saturated fats from cream into a single block is how butter is manufactured. As a result, butter contains more than half of its calories as saturated fat. Saturated fats can be found in up to 7 grams per tablespoon of butter.

  • Soft Cheese:

Different forms of cheese are made from milk that has varying quantities of fat. In general, fat softens cheese, therefore soft cheeses like brie have more lipids. 


Disorders of Lipid Metabolism

Fabry disease

Lipid metabolism disorders (including inborn errors of lipid metabolism) are diseases that cause problems with fat breakdown or synthesis (or fat-like substances). Lipid metabolism problems are related with an increase in plasma lipid concentrations in the blood, such as LDL cholesterol, VLDL cholesterol, and triglycerides, which most usually contribute to cardiovascular disease. A lot of the time, these problems are genetic, which means they are handed on from parent to kid via their DNA.

 Gaucher's disease (types I, II, and III), Niemann–Pick disease, Tay–Sachs disease, and Fabry's disease are all disorders in which the body's lipid metabolism is disrupted.

1. Gaucher's disease:

Gaucher disease is caused by an accumulation of specific fatty compounds in various organs, most notably your spleen and liver. This causes these organs to expand and has the potential to impair their function.Fatty molecules can also accumulate in bone tissue, weakening it and increasing the risk of fracture. If your bone marrow is harmed, it can impair your blood's capacity to clot.

In persons with Gaucher disease, an enzyme that breaks down these fatty compounds does not function correctly. Enzyme replacement therapy is frequently used in treatment.Gaucher illness is a hereditary ailment that is particularly frequent among Jews of Eastern and Central European descent (Ashkenazi). Symptoms might manifest themselves at any age.

Gaucher disease is classified into several forms, and the signs and symptoms of the disease vary greatly even within the same type. Type 1 is by far the most prevalent.Siblings, even identical twins, with the condition might have varying degrees of severity. Some persons with Gaucher illness exhibit relatively little or no symptoms.

The following issues affect the majority of Gaucher disease patients to varied degrees:

  • Abdominal complaints: Because the liver and especially the spleen can enlarge dramatically, the abdomen can become painfully distended.
  • Skeletal abnormalities: Gaucher disease can cause bone weakness, increasing the likelihood of painful fractures. It can also disrupt the blood circulation to your bones, causing sections of the bone to die.
  • Blood disorders: Anemia (a reduction in healthy red blood cells) can cause extreme weariness. Gaucher disease also damages the clotting cells, resulting in easy bruising and nosebleeds.

Gaucher disease, which affects the brain more rarely, can produce irregular eye movements, muscular stiffness, swallowing difficulty, and seizures. One rare variant of Gaucher illness develops in infancy and usually kills the child before the age of two.


2. Niemann–Pick disease:

Niemann-Pick disease is a rare, genetic condition that impairs the body's capacity to digest fat (cholesterol and lipids) within cells. These cells malfunction and eventually die. The brain, nerves, liver, spleen, bone marrow, and, in extreme instances, the lungs can all be affected by Niemann-Pick disease.

This disorder causes symptoms due to the gradual loss of function of nerves, the brain, and other organs. Niemann-Pick disease can strike at any age, although it primarily affects youngsters. The condition has no known treatment and can be lethal. Treatment focuses on assisting patients in coping with their symptoms.

Niemann-Pick signs and symptoms may include:

  • Clumsiness and difficulty walking.
  • Excessive muscle contractions (dystonia) or eye movements.
  • Sleep disturbances.
  • Difficulty swallowing and eating.
  • Recurrent pneumonia.

Kinds A, B, and C are the three primary types of Niemann-Pick. The signs and symptoms will vary depending on the kind and severity of your ailment. Some type A newborns will exhibit signs and symptoms within the first few months of life. Type B patients may not exhibit symptoms for years and have a greater chance of living to maturity. People with type C may not exhibit any symptoms until they reach maturity. 


3. Tay–Sachs disease:

Tay-Sachs disease is a rare genetic illness that is handed down from father to son. It is caused by the lack of an enzyme that aids in the breakdown of fatty compounds. These fatty molecules, known as gangliosides, accumulate to hazardous amounts in the brain and spinal cord, impairing nerve cell activity.

Signs and symptoms of the most frequent and severe form of Tay-Sachs disease appear between the ages of 3 and 6 months. As the condition advances, growth slows and muscles weaken. Seizures, visual and hearing loss, paralysis, and other serious problems develop as a result of this. Children with this kind of Tay-Sachs disease have a short lifespan.

Some children have the juvenile form of Tay-Sachs disease and may live into their adolescence. Some people may have a late-onset variant of Tay-Sachs disease, which is frequently milder than versions that begin in childhood.

In the most frequent and severe type, known as infantile form, a newborn often begins to develop signs and symptoms between the ages of 3 and 6 months. Survival is generally limited to a few years. Among the signs and symptoms are:

  • Exaggerated startle response when the baby hears loud noises.
  • "Cherry-red" spots in the eyes.
  • Loss of motor skills, including turning over, crawling and sitting up.
  • Muscle weakness, progressing to paralysis.
  • Movement problems.
  • Seizures.
  • Vision loss and blindness.
  • Hearing loss and deafness.
  • Problems swallowing.
  • Loss of mental functions and a lack of response to surroundings.
  • Growth in head size (progressive macrocephaly).


4. Fabry disease:

It is a hereditary condition caused by the accumulation of a specific form of fat termed globotriaosylceramide in the body's cells. This accumulation, which begins in childhood, generates signs and symptoms that impact numerous regions of the body.

Fabry disease is distinguished by episodes of pain, particularly in the hands and feet (acroparesthesias); clusters of small, dark red spots on the skin known as angiokeratomas; a decreased ability to sweat (hypohidrosis); cloudiness or streaks in the front part of the eye (corneal opacity or corneal verticillata); gastrointestinal problems; ringing in the ears (tinnitus); and hearing loss.

Fabry disease can also lead to potentially fatal consequences such as increasing kidney failure, a heart attack, or a stroke. Some people are affected by milder versions of the condition that arise later in life and just impact the heart or kidneys.



Lipid profile test

Lipid metabolism include the synthesis of structural and functional lipids (such as phospholipids, glycolipids, sphingolipids, cholesterol, prostaglandins, and so on) specific to various tissues, as well as the breakdown of lipids to meet the body's metabolic demands (e.g., energy production).

Lipid metabolism is in a state of dynamic balance at all times. This means that some lipids are continually oxidized to fulfill the metabolic demands of the organism, whilst others are produced and stored.

Lipids are involved in lipid metabolism illnesses such as Gaucher disease and Tay-Sachs disease. Fats or fat-like compounds are referred to as lipids. Oils, fatty acids, waxes, and cholesterol are among them. You may not have enough enzymes to break down lipids if you have one of these illnesses. Alternatively, the enzymes may not function effectively, preventing your body from converting fats into energy. 

They induce an unhealthy buildup of lipids in your body. This can cause harm to your cells and tissues over time, particularly in the brain, peripheral nervous system, liver, spleen, and bone marrow. Many of these illnesses can be life-threatening or even deadly.

These conditions are inherited. Blood tests are used to check newborn newborns for certain of these. If one of these problems runs in the family, parents can obtain genetic testing to discover if they carry the gene. Other genetic testing can determine if the fetus has the condition or has the disorder's gene.