What is the Difference Between Lipogenesis and Lipolysis

The main difference between lipogenesis and lipolysis is that lipogenesis is the fat synthesis, whereas lipolysis is the fat breakdown.

Lipogenesis and lipolysis are two metabolic processes of fat that occur in the body. The balance between lipogenesis and lipolysis determines fat deposits. 

Key Areas Covered

1. What is Lipogenesis
– Definition, Facts, Features
2. What is Lipolysis
– Definition, Facts, Features
3. Similarities Between Lipogenesis and Lipolysis
– Outline of Common Features
4. Difference Between Lipogenesis and Lipolysis
– Comparison of Key Differences

Key Terms 

Lipogenesis, Lipolysis

What is Lipogenesis

Lipogenesis is a metabolic process stimulated by a high-carbohydrate diet. However, fasting and polyunsaturated fatty acids inhibit lipogenesis. Also, it is partly mediated by hormones: growth hormone and leptin inhibit lipogenesis, and insulin increases lipogenesis. The balance between lipogenesis and lipolysis determines fat accumulation in the body. Lipogenesis is responsible for the fatty acid synthesis and the subsequent triglyceride synthesis in liver and adipose tissue. Adipogenesis is a separate process of differentiation of pre-adipocytes into mature fat cells.

Figure 1: Lipogenesis

Furthermore, lipogenesis is sensitive to changes in diet. Polyunsaturated fatty acids suppress the expression of genes such as fatty acid synthase in the liver. Thereby, they inhibit fatty acid synthesis. Other genes suppressed by polyunsaturated fatty acids include spot14 and stearoyl-CoA desaturase. At the same time, carbohydrate-rich diets stimulate lipogenesis leading to postprandial triglyceride levels in the plasma. Meanwhile, fasting increases the rate of lipolysis, leading to the net loss of triglycerides from adipose cells.

What is Lipolysis

Lipolysis is the metabolic process of breaking down triglycerols into glycerol and free fatty acids. Adipose tissue in the body stores fats used for energy, heat, and insulation. During starvation, fat is the primary source of energy in the body. Also, lipolysis’s glycerol is the main carbon source in gluconeogenesis occurring in the liver. Additionally, free fatty acids are transported bound to albumin in the blood. Beta oxidation is the process that converts free fatty acids into ketone bodies. Other byproducts of beta-oxidation, such as ATP and NADH, promote gluconeogenesis. However, ketone bodies serve as an energy source in the brain. It decreases the consumption of glucose.

Figure 2: Lipolysis

Moreover, free fatty acids are essential for energy production in cells throughout the body except in adipose tissues. On the other hand, adipose triglyceride lipase (ATGL), monoglyceride lipase (MGL), and hormone-sensitive lipase (HSL) are the main enzymes that involve in lipolysis.

Similarities Between Lipogenesis and Lipolysis

• Lipogenesis and lipolysis are two metabolic processes of fat.
• They are essential for the determination of fat build-up in the body.

Difference Between Lipogenesis and Lipolysis

Definition

Lipogenesis refers to a process of fatty acid and triglyceride synthesis from glucose or other substrates. Meanwhile, lipolysis refers to the breakdown of lipids, such as fat by hydrolysis to release fatty acids. 

Occurrence

Lipogenesis occurs after a carbohydrate-rich meal, while lipolysis occurs during starvation.

Hormonal State

Lipogenesis occurs in a high insulin/glucagon ratio, while lipolysis occurs in a low insulin/glucagon ratio.

Major Tissue Site

Lipogenesis primarily occurs in the liver, while lipolysis occurs in skeletal muscles and the liver. 

Subcellular Location

Lipogenesis occurs in the cytosol, while lipolysis primarily occurs in mitochondria.

Carriers of Acetyl Groups between Mitochondria and Cytosol

Citrate is the carrier of acetyl groups between mitochondria to cytosol in lipogenesis, while carnitine is the carrier of acetyl groups between cytosol to mitochondria in lipolysis. 

Coenzymes

Lipogenesis uses NADPH, while lipolysis uses NAD+ and FAD.

Activator

Citrate is the activator of lipogenesis, while no activator is found for lipolysis.

Inhibitor

Long-chain fatty acyl CoA is the inhibitor of lipogenesis, while malonyl CoA is the inhibitor of lipolysis.

Product

Palmitate is the product of lipogenesis, while acetyl CoA is the product of lipolysis.

Steps

The steps of lipogenesis include condensation, reduction, dehydration, and reduction, while the steps of lipolysis include dehydrogenation, hydration, dehydrogenation, and thiolysis.

Conclusion

In brief, lipogenesis and lipolysis are two metabolic processes of fat. Lipogenesis is the synthesis of fatty acids. It occurs in the liver in a high-carbohydrate diet. Also, it occurs in a high insulin/glucagon ratio. Citrate is the activator of lipogenesis, and NADPH is used in lipogenesis as a reductant. Condensation, reduction, dehydration, and reduction are the steps of lipogenesis. In comparison, lipolysis is the breakdown of fat. It yields acetyl CoA. It occurs during starvation and low insulin/glucagon ratios. Also, it occurs in the skeletal muscles and liver. Additionally, it uses NAD+ and FAD. Dehydrogenation, hydration, dehydrogenation, and thiolysis are the steps of lipolysis. 

References:

1. Kersten S. Mechanisms of nutritional and hormonal regulation of lipogenesis. EMBO Rep. 2001 Apr;2(4):282-6. doi: 10.1093/embo-reports/kve071. PMID: 11306547; PMCID: PMC1083868.
2. Edwards M, Mohiuddin SS. Biochemistry, Lipolysis. [Updated 2022 Jul 18]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-.

Image Courtesy:

1. “Palmitic acid synthesis fr” By Foobar – Own work (CC-BY 2.5) via Commons Wikimedia
2. “Metabolism1” By Cruithne9 – Own Work (CC-BY SA 4.0) via Commons Wikimedia