Metabolic-Associated Steatotic Liver Disease (MASLD)

MASLD (Metabolic-Associated Steatotic Liver Disease) is the new name, adopted by global consensus in 2023, for what was previously called Non-Alcoholic Fatty Liver Disease (NAFLD). The rename is more than cosmetic — it anchors the diagnosis to its metabolic root causes and eliminates the stigmatizing "non-alcoholic" framing. MASLD affects an estimated 38% of adults worldwide, making it the most common chronic liver disease on earth. Its severe inflammatory form, MASH (Metabolic-Associated Steatohepatitis, formerly NASH), can progress through fibrosis to cirrhosis and hepatocellular carcinoma — yet most patients are never diagnosed until damage is advanced.

  1. Overview
  2. The 2023 Rename: NAFLD → MASLD
  3. Pathophysiology
  4. Clinical Presentation
  5. Diagnosis
  6. Fibrosis Staging and Risk Stratification
  7. Treatment
  8. Pharmacotherapy
  9. Research Papers
  10. Connections
  11. Featured Videos

Overview

MASLD is defined by hepatic steatosis — fat accumulation exceeding 5% of hepatocytes — in a person with at least one cardiometabolic risk factor: BMI >25 kg/m² (or waist circumference >94 cm men / >80 cm women), type 2 diabetes, hypertension, dyslipidemia (elevated triglycerides or low HDL), or impaired fasting glucose. A minority alcohol threshold (men ≤30 g/day, women ≤20 g/day) is retained in the definition.

The disease spectrum:

Cardiovascular disease — not liver failure — is the leading cause of death in MASLD. Patients with MASLD carry a 2-fold increased risk of cardiovascular events independent of traditional risk factors.

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The 2023 Rename: NAFLD → MASLD

The Delphi consensus process published in June 2023 (endorsed by EASL, AASLD, ALEH, APASL, and over 200 societies) replaced NAFLD/NASH with MASLD/MASH. Key rationale:

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Pathophysiology

The "two-hit" model has been replaced by a multi-parallel-hit framework.

Hit 1 — Lipid accumulation: Insulin resistance causes excess fatty acid flux to the liver from adipose tissue lipolysis, simultaneously driving de novo lipogenesis (DNL) via SREBP-1c activation. Hepatocytes accumulate triglycerides as lipid droplets. This steatosis is largely non-toxic.

Hit 2+ — Lipotoxicity and inflammation: Free fatty acids — particularly saturated fatty acids (palmitate, stearate) and their ceramide derivatives — are directly toxic to hepatocytes. They activate endoplasmic reticulum (ER) stress pathways (unfolded protein response), promote mitochondrial dysfunction, and trigger hepatocyte apoptosis and necroptosis. Damaged hepatocytes release damage-associated molecular patterns (DAMPs) that activate hepatic Kupffer cells and stellate cells.

Hepatic stellate cell activation and fibrosis: Activated stellate cells transform into myofibroblasts that produce collagen I and III, laying down perisinusoidal and pericellular fibrosis — the "chicken-wire" pattern characteristic of MASLD/MASH on biopsy.

Gut-liver axis: Intestinal dysbiosis increases gut permeability, delivering bacterial LPS to the liver via the portal vein, amplifying Kupffer cell TLR4 activation and pro-inflammatory cytokine (TNF-α, IL-6, IL-1β) production.

Genetic modifiers: PNPLA3 (I148M variant) and TM6SF2 (E167K) substantially increase susceptibility to steatosis and fibrosis. PNPLA3 I148M homozygotes have a 3-fold increased risk of advanced fibrosis compared to wild-type.

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Clinical Presentation

Most patients with MASLD are asymptomatic; the condition is discovered incidentally on liver function tests or imaging. When symptoms do occur:

Symptoms:

Laboratory findings:

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Diagnosis

Diagnosis requires (1) confirming steatosis, (2) excluding other causes, and (3) staging fibrosis.

Imaging for steatosis:

Non-invasive fibrosis assessment:

Liver biopsy: required for definitive MASH diagnosis and precise fibrosis staging when non-invasive tests are discordant, before initiating resmetirom, or in clinical trials. NAS (NAFLD Activity Score) grades steatosis (0–3), lobular inflammation (0–3), and hepatocyte ballooning (0–2); NAS ≥5 correlates with MASH diagnosis. Fibrosis staged F0–F4 on the Kleiner/Brunt system.

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Fibrosis Staging and Risk Stratification

Fibrosis stage is the single most important prognostic variable in MASLD — more important than NAS score, transaminase levels, or steatosis grade.

Stage Description 10-year liver-related mortality
F0 No fibrosis ~0.5%
F1 Perisinusoidal or periportal fibrosis ~1–2%
F2 Perisinusoidal + periportal fibrosis ~3–5%
F3 Bridging fibrosis ~10–15%
F4 Cirrhosis ~30–50%

The AASLD/EASL guidelines recommend FIB-4 as the initial triage tool at primary care level:

MASLD-related cirrhosis complications mirror other causes: portal hypertension, esophageal varices, ascites, hepatic encephalopathy, spontaneous bacterial peritonitis. HCC surveillance (ultrasound ± AFP every 6 months) is recommended from cirrhosis diagnosis; notably, MASLD-related HCC also occurs in non-cirrhotic patients with advanced fibrosis (F3).

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Treatment

Weight loss is the cornerstone — the only intervention proven to reduce fibrosis and achieve MASH resolution in clinical practice.

Weight loss targets:

Dietary approaches:

Exercise:

Bariatric/metabolic surgery:

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Pharmacotherapy

As of 2024, one specific pharmacotherapy is FDA-approved for MASH.

Resmetirom (Rezdiffra, Madrigal Pharmaceuticals):

GLP-1 receptor agonists (semaglutide, tirzepatide):

Pioglitazone (thiazolidinedione):

SGLT2 inhibitors (empagliflozin, dapagliflozin):

Vitamin E (800 IU/day alpha-tocopherol):

Not recommended for MASLD:

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Research Papers

  1. PMID 37363454 — Rinella ME et al. "A multisociety Delphi consensus statement on new fatty liver disease nomenclature." Hepatology 2023. (The 2023 MASLD rename consensus paper.)
  2. PMID 37506885 — Harrison SA et al. "A Phase 3, Randomized, Controlled Trial of Resmetirom in NASH with Liver Fibrosis." New England Journal of Medicine 2024. (MAESTRO-NASH trial.)
  3. PMID 22508706 — Sanyal AJ et al. "Pioglitazone, Vitamin E, or Placebo for Nonalcoholic Steatohepatitis." New England Journal of Medicine 2010. (PIVENS trial.)
  4. PMID 31726529 — Younossi ZM et al. "Global epidemiology of nonalcoholic fatty liver disease." Hepatology 2016. (Global prevalence meta-analysis.)
  5. PMID 28930595 — Angulo P et al. "Liver Fibrosis, but No Other Histologic Features, Is Associated with Long-term Outcomes of Patients with Nonalcoholic Fatty Liver Disease." Gastroenterology 2015. (Fibrosis stage as key prognostic variable.)
  6. PMID 26122767 — Vilar-Gomez E et al. "Weight Loss Through Lifestyle Modification Significantly Reduces Features of Nonalcoholic Steatohepatitis." Gastroenterology 2015. (Weight loss targets.)
  7. PMID 23481461 — Promrat K et al. "Randomized controlled trial testing the effects of weight loss on nonalcoholic steatohepatitis." Hepatology 2010.
  8. PMID 37182400 — Newsome PN et al. "A Placebo-Controlled Trial of Subcutaneous Semaglutide in Nonalcoholic Steatohepatitis." New England Journal of Medicine 2021. (Phase 2 semaglutide.)
  9. PMID 26933168 — Romeo S et al. "Genetic variation in PNPLA3 confers susceptibility to nonalcoholic fatty liver disease." Nature Genetics 2008. (PNPLA3 variant.)
  10. PMID 33306989 — Lazarus JV et al. "Advancing the global public health agenda for NAFLD." Nature Reviews Gastroenterology & Hepatology 2022.
  11. PMID 25941327 — Byrne CD, Targher G. "NAFLD: A multisystem disease." Journal of Hepatology 2015. (Cardiovascular risk in NAFLD.)
  12. PMID 35413278 — Chalasani N et al. "AASLD Practice Guidance on the clinical assessment and management of nonalcoholic fatty liver disease." Hepatology 2023.

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Connections

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