Lipogenesis
| Category | Biology |
|---|---|
| Also known as | De Novo Lipogenesis, Fatty Acid Synthesis, Fat Synthesis, DNL |
| Last updated | 2026-04-14 |
| Reading time | 4 min read |
| Tags | metabolismfat-storageliverinsulinadipose |
Overview
Lipogenesis — specifically de novo lipogenesis (DNL) — is the biosynthetic pathway that converts excess acetyl-CoA, primarily derived from carbohydrate metabolism, into fatty acids. These fatty acids are subsequently esterified with glycerol to form triglycerides for storage in adipose tissue or export as very-low-density lipoproteins (VLDL) from the liver. Lipogenesis occurs mainly in the liver (in humans) and to a lesser extent in adipose tissue.
This pathway is activated in the fed state when energy intake exceeds immediate needs, and it is strongly stimulated by insulin and carbohydrate-rich diets. Conversely, lipogenesis is suppressed during fasting, when the body shifts toward beta-oxidation and ketogenesis to mobilize stored fat for energy.
How It Works
From Glucose to Fatty Acids
- Substrate generation — Glycolysis converts glucose to pyruvate, which enters the mitochondria and is converted to acetyl-CoA by pyruvate dehydrogenase. Acetyl-CoA enters the Krebs cycle and condenses with oxaloacetate to form citrate.
- Citrate export — When mitochondrial energy charge is high, excess citrate is exported to the cytoplasm via the citrate transport system.
- Acetyl-CoA regeneration — ATP-citrate lyase cleaves cytoplasmic citrate back into acetyl-CoA and oxaloacetate.
- Carboxylation — Acetyl-CoA carboxylase (ACC) converts acetyl-CoA to malonyl-CoA — the committed step in fatty acid synthesis.
- Chain elongation — Fatty acid synthase (FAS), a large multifunctional enzyme, sequentially adds two-carbon units from malonyl-CoA to build palmitate (C16:0), consuming NADPH as the reducing agent.
- Modification — Palmitate can be further elongated and desaturated by elongases and desaturases in the endoplasmic reticulum.
- Esterification — Fatty acids are combined with glycerol-3-phosphate to form triglycerides.
NADPH Supply
Lipogenesis requires large quantities of NADPH, supplied primarily by the pentose phosphate pathway and by the malic enzyme (which converts malate to pyruvate in the cytoplasm).
Regulation
ACC is the primary regulatory enzyme, controlled by allosteric regulation (activated by citrate, inhibited by palmitoyl-CoA), covalent modification (inactivated by AMPK phosphorylation), and transcriptional regulation. Insulin stimulates lipogenesis through SREBP-1c (sterol regulatory element-binding protein), which upregulates ACC, FAS, and other lipogenic genes. Glucagon and AMPK inhibit lipogenesis.
Key Components
- Acetyl-CoA carboxylase (ACC) — Rate-limiting enzyme producing malonyl-CoA
- Fatty acid synthase (FAS) — The multienzyme complex building palmitate
- SREBP-1c — Transcription factor driving lipogenic gene expression
- Malonyl-CoA — Both a lipogenic intermediate and an inhibitor of beta-oxidation via CPT1
- NADPH — The reducing agent essential for fatty acid chain elongation
Peptide Connections
Lipogenesis is primarily regulated by peptide hormones controlling the fed-fasted metabolic axis:
Insulin is the master activator of lipogenesis. Through the insulin signaling cascade, insulin stimulates SREBP-1c processing and translocation to the nucleus, upregulating transcription of ACC, FAS, and other lipogenic enzymes. Insulin also activates ACC by promoting its dephosphorylation. Chronic hyperinsulinemia, as seen in insulin resistance, drives excessive hepatic lipogenesis — a major contributor to non-alcoholic fatty liver disease (NAFLD).
Semaglutide and other GLP-1 receptor agonists reduce hepatic lipogenesis through multiple mechanisms. By improving insulin sensitivity and reducing hyperinsulinemia, these agents decrease the chronic lipogenic drive. Clinical trials have demonstrated significant reductions in liver fat content in patients treated with semaglutide, with improvements correlating with weight loss and metabolic improvement.
Tirzepatide, a dual GIP/GLP-1 receptor agonist, has shown even greater reductions in liver fat content in clinical studies. The combined incretin effect appears to more potently suppress hepatic de novo lipogenesis and improve the balance between fat synthesis and oxidation.
Glucagon suppresses lipogenesis by activating AMPK (indirectly) and by opposing insulin's transcriptional effects on lipogenic genes. The glucagon-to-insulin ratio is a key determinant of whether the liver is in a lipogenic or oxidative state.
Clinical Significance
Excessive hepatic lipogenesis is a central pathogenic mechanism in non-alcoholic fatty liver disease (NAFLD) and its progressive form, non-alcoholic steatohepatitis (NASH). In insulin-resistant states, the liver continues to respond to insulin's lipogenic signaling (via SREBP-1c) even while becoming resistant to insulin's glucose-lowering effects — a phenomenon termed selective insulin resistance.
Dysregulated lipogenesis also contributes to hypertriglyceridemia, visceral adiposity, and the metabolic syndrome. Pharmacological targeting of lipogenic enzymes (ACC inhibitors) is an active area of drug development for NASH.
Related Topics
- Beta-Oxidation — The opposing pathway that breaks down fatty acids
- Ketogenesis — Alternative fate of acetyl-CoA when lipogenesis is suppressed
- Insulin Signaling Cascade — Hormonal driver of lipogenic gene expression
- Pentose Phosphate Pathway — Supplies NADPH for fatty acid synthesis
- Glycolysis — Provides the acetyl-CoA substrate for lipogenesis
Related entries
- Beta-Oxidation— Beta-oxidation is the mitochondrial process that breaks down fatty acids into acetyl-CoA units for energy production, serving as the primary pathway for fat metabolism.
- Gluconeogenesis— Gluconeogenesis is the metabolic pathway by which the liver and kidneys synthesize new glucose from non-carbohydrate precursors, maintaining blood sugar during fasting and prolonged exercise.
- Glycolysis— Glycolysis is the universal cytoplasmic pathway that splits glucose into two molecules of pyruvate, generating ATP and NADH while serving as the gateway to aerobic and anaerobic energy metabolism.
- Insulin Signaling— The molecular cascade initiated by insulin binding to its receptor, driving glucose uptake, glycogen synthesis, and metabolic regulation across multiple tissues.
- Ketogenesis— Ketogenesis is the hepatic process of converting excess acetyl-CoA from fatty acid oxidation into ketone bodies, providing an alternative fuel source for the brain and other tissues during fasting.
- Beta-Oxidation— The mitochondrial cycle that breaks down fatty acids into acetyl-CoA units, yielding large quantities of ATP during fasting, exercise, and fat metabolism.
- Gluconeogenesis— The hepatic and renal synthesis of glucose from non-carbohydrate precursors such as lactate, amino acids, and glycerol during fasting and exercise.
- Ketogenesis— The hepatic synthesis of ketone bodies from acetyl-CoA during fasting and carbohydrate restriction, providing an alternative fuel for brain and peripheral tissues.