Dr. Ben Bikman explores the misunderstood role of glucagon, insulin’s often-overlooked metabolic counterpart.
While insulin encourages fat storage and glucose uptake, glucagon signals the body to mobilize and burn stored energy. Contrary to popular belief, glucagon does not stimulate fat release from adipose tissue in humans. Instead, its fat-burning effects occur primarily in the liver, where it enhances fatty acid oxidation, ketone production, and energy expenditure.
Glucagon’s power lies in shifting the metabolic balance through the insulin-to-glucagon ratio—a key determinant of whether the body stores or burns fat. Ben also unpacks the liver's molecular response to glucagon, including activation of mitochondrial fat-burning enzymes and ketone formation. Human studies now confirm that glucagon increases liver fat oxidation, making it a valuable target in new weight-loss drugs.
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Glucagon and the insulin-to-glucagon ratio
Glucagon sits beside insulin as the key counter-hormone in fat-loss metabolism.
- Insulin drives glucose uptake, fat storage, and energy storage.
- Glucagon drives glycogen breakdown, liver fat oxidation, and ketone production.
- The insulin-to-glucagon ratio determines whether metabolism moves toward storage after carbohydrate intake or energy release during fasting and low carbohydrate intake.
- Type 2 diabetes disrupts this system when insulin and glucagon are both high, leaving the liver with a glucose-output signal while tissues are insulin resistant.
The adipose-tissue misconception The textbook idea that glucagon directly pulls fat out of human adipose tissue is incorrect for humans.
- Rodent data made glucagon look like a direct adipose lipolysis hormone through hormone-sensitive lipase activation.
- Human white fat has very low or undetectable glucagon receptor expression in mature adipocytes.
- The 2001 microdialysis work found no local glycerol rise in abdominal fat even with glucagon raised three to fourfold.
- The 2020 human-adipocyte work found low and variable receptor expression and meaningful lipolysis only at superphysiological glucagon levels.
- The 2022 adipocyte-specific receptor knockout mouse work found no change in fasting-induced lipolysis or body composition.
- Human fat loss is not glucagon yanking triglycerides directly out of fat cells.
The liver mechanism Glucagon's fat-burning work occurs in the liver, where glucagon receptors are abundant.
- Glucagon activates adenylate cyclase, raises cyclic AMP, activates PKA, and inactivates acetyl-CoA carboxylase.
- Inactivating acetyl-CoA carboxylase stops new fat synthesis and removes malonyl-CoA inhibition of CPT1.
- CPT1 then moves more fatty acids into mitochondria for oxidation.
- Glucagon also increases CPT1 transcription through CREB, expanding the liver's capacity to burn fat.
- The Yale Nature work connects glucagon to intrahepatic lipolysis through INSP3R1, calcium release, and ATGL.
- The 2024 Cell Metabolism human study shows glucagon infusion raising hepatic mitochondrial oxidation by about 50% in fatty liver disease.
Ketones and the insulin brake Glucagon-driven liver fat oxidation connects to ketone production when insulin is low.
- During fasting, oxaloacetate is diverted toward gluconeogenesis, leaving acetyl-CoA to condense into acetoacetate and beta-hydroxybutyrate.
- Liver-cell work supports glucagon as a driver of fatty acid oxidation and ketogenesis.
- The 2020 mouse work shows ketone production can persist without glucagon signaling during fasting.
- Low insulin is necessary; high insulin can overpower glucagon's fat-burning and ketone-producing effects.
Drug implications and lifestyle implications GLP-1 drugs, dual agonists, and triple agonists show why glucagon biology matters clinically.
- Semaglutide can produce about 15% weight loss over a little more than a year, mainly through appetite suppression, slower gastric emptying, and glucose control.
- A Boehringer Ingelheim dual GLP-1/glucagon agonist at 4.8 mg produced about 14.7% weight loss over 46 weeks and stronger liver-fat effects than GLP-1 alone.
- In MASH/NASH, the same dual-agonist program is tied to 83% biopsy-based steatohepatitis resolution versus 18% on placebo and improved fibrosis scores.
- Retatrutide adds GIP to GLP-1 and glucagon and produced nearly 24% weight loss at 48 weeks at the highest dose.
- These drugs are not routine standalone weight-loss tools; their strongest role is low-dose craving control paired with a smart low-carbohydrate diet.
- Reduced carbohydrate intake and fasting can improve glucagon signaling by shifting the ratio toward fuel release.
References
- [04:09] Glucagon and the Insulin:Glucagon Ratio in Diabetes and Other Catabolic Illnesses — https://doi.org/10.2337/diab.20.12.834
- [08:02] Physiological Levels of Glucagon Do Not Influence Lipolysis in Abdominal Adipose Tissue as Assessed by Microdialysis — https://doi.org/10.1210/jcem.86.5.7460
- [08:32] Direct effects of glucagon on glucose uptake and lipolysis in human adipocytes — https://doi.org/10.1016/j.mce.2019.110696
- [09:06] Glucagon receptor signaling at white adipose tissue does not regulate lipolysis — https://doi.org/10.1152/ajpendo.00078.2022
- [11:50] Glucagon stimulates gluconeogenesis by INSP3R1-mediated hepatic lipolysis — https://doi.org/10.1038/s41586-020-2074-6
- [12:26] Glucagon promotes increased hepatic mitochondrial oxidation and pyruvate carboxylase flux in humans with fatty liver disease — https://doi.org/10.1016/j.cmet.2024.07.023
- [14:59] The Limited Role of Glucagon for Ketogenesis During Fasting or in Response to SGLT2 Inhibition — https://doi.org/10.2337/db19-1216
- [16:25] Once-Weekly Semaglutide in Adults with Overweight or Obesity — https://doi.org/10.1056/NEJMoa2032183
- [17:27] Glucagon and GLP-1 receptor dual agonist survodutide for obesity: a randomised, double-blind, placebo-controlled, dose-finding phase 2 trial — https://doi.org/10.1016/S2213-8587(23)00356-X
- [17:51] A Phase 2 Randomized Trial of Survodutide in MASH and Fibrosis — https://doi.org/10.1056/NEJMoa2401755
- [18:50] Triple-Hormone-Receptor Agonist Retatrutide for Obesity — https://doi.org/10.1056/NEJMoa2301972