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Nomenclature and definitions

TL;DR — In June 2023 a modified Delphi process run by three pan-national liver societies, with 236 panellists from 56 countries, replaced "non-alcoholic fatty liver disease" with metabolic dysfunction-associated steatotic liver disease (MASLD): 74% of respondents judged the old nomenclature sufficiently flawed to warrant change, 61% found "nonalcoholic" stigmatising and 66% found "fatty" stigmatising (Rinella 2023, PMID 37363821 / PMID 37364790). The change is not cosmetic — MASLD requires at least one of five cardiometabolic criteria, whereas NAFLD required only the absence of significant alcohol intake and other causes. Empirically the two populations almost coincide: Cohen's κ 0.968 (95% CI 0.962–0.973) in NHANES III, with 5.29% of NAFLD cases failing MASLD criteria and no mortality difference (Younossi 2024, PMID 38286339); 99% overlap in the NHANES 2017–March 2020 elastography sample (Lee 2024, PMID 37732946). The genuinely new object is MetALD, the overlap band of metabolic dysfunction plus intermediate alcohol intake (140–350 g/week in women, 210–420 g/week in men), which is neither a rename nor a subset of anything previously counted, and which carries a 1.56-fold higher rate of adverse liver outcomes than MASLD (Ochoa-Allemant 2025, PMID 40522656). A competing 2020 proposal, MAFLD, remains in parallel use and is not identical to MASLD (Eslam 2020, PMID 32044314).

The three vocabularies, and why searches must union them

Term Introduced Positive requirement Alcohol handling Status
NAFLD / NASH 1980s–2000s usage none — diagnosis of exclusion exclusion criterion (<20 g/d women, <30 g/d men in most studies) superseded 2023, but ~all evidence generated under it
MAFLD 2020 (Eslam 2020, PMID 32044314) steatosis + (overweight/obesity or T2D or ≥2 metabolic abnormalities) not an exclusion — permits concurrent alcohol/viral disease parallel use; endorsed by a multi-stakeholder group (Méndez-Sánchez 2022, PMID 35248211)
MASLD (within SLD) 2023 (Rinella 2023, PMID 37363821) steatosis + ≥1 of 5 cardiometabolic criteria intake below MetALD threshold current in AASLD/EASL/APASL guidance

The practical consequence for this knowledge base is a search rule. A query on the new name alone returns a literature that appears to begin in 2023: on 2026-09-02, metabolic dysfunction-associated steatotic liver disease OR MASLD returned 50,200 records while nonalcoholic fatty liver disease OR NAFLD returned 51,746 and nonalcoholic steatohepatitis OR MASH returned 53,007, and the union (MASLD OR NAFLD OR MASH OR NASH OR "steatotic liver disease") returned 78,992. Every search behind a claim on these pages unions both vocabularies; an absence found under one name is not an absence.

The second consequence is descriptive discipline. Where a study enrolled under NAFLD/NASH criteria — which is nearly every trial and cohort cited across this condition — the page says so. The 2023 statement is a reclassification of a category, not a retrospective re-diagnosis of individuals, and the two are not interchangeable when the inclusion criteria are what is at stake.

The 2023 Delphi process

The process was led by three large pan-national liver associations, ran four online surveys and two hybrid meetings, and set consensus a priori at a 67% supermajority. Response rates were 87%, 83%, 83% and 78% across rounds. An independent committee external to the process made the final call on the acronym and its diagnostic criteria (Rinella 2023, PMID 37363821 / PMID 37364790; also co-published in Ann Hepatol, PMID 37364816).

Four decisions came out of it:

  1. "Steatotic liver disease" (SLD) became the umbrella term for hepatic steatosis of any aetiology.
  2. "Steatohepatitis" was retained — the panel judged it an important pathophysiological concept, so NASH → MASH rather than being abolished.
  3. MASLD replaced NAFLD, with a positive cardiometabolic requirement.
  4. MetALD was created for the band between MASLD and alcohol-related liver disease, and cryptogenic SLD for steatosis with no metabolic parameter and no known cause.

The five cardiometabolic criteria

MASLD requires hepatic steatosis plus at least one of the following (Rinella 2023, PMID 37363821; summarised for adults in Tilg 2026, PMID 41212550):

# Criterion (adult thresholds)
1 BMI ≥25 kg/m² (≥23 in Asian populations) or waist circumference >94 cm (M) / >80 cm (F)
2 Fasting glucose ≥5.6 mmol/L, 2-h post-load ≥7.8 mmol/L, HbA1c ≥5.7%, type 2 diabetes, or treatment for T2D
3 Blood pressure ≥130/85 mmHg or antihypertensive treatment
4 Plasma triglycerides ≥1.70 mmol/L or lipid-lowering treatment
5 HDL-cholesterol ≤1.0 mmol/L (M) / ≤1.3 mmol/L (F) or lipid-lowering treatment

Because the thresholds are permissive — one criterion suffices, and prediabetes and treated hypertension both qualify — the criteria capture the great majority of people who would previously have been labelled NAFLD. In the Younossi tertiary-care database of 6,429 patients, 99% met MASLD criteria and 95% met them on BMI alone (PMID 38286339). This is the empirical basis for treating pre-2023 NAFLD evidence as applicable to MASLD, and it is also the reason the criteria have been criticised as insufficiently discriminating (see Open questions).

MetALD: the genuinely new category

MetALD denotes metabolic dysfunction-associated steatosis in people whose weekly alcohol intake sits between the MASLD ceiling and the ALD floor: 140–350 g/week (20–50 g/day) for women and 210–420 g/week (30–60 g/day) for men (Rinella 2023, PMID 37363821; thresholds restated in Kalligeros 2024, PMID 37949334).

Cohort n MASLD MetALD ALD Source
NHANES 2017–March 2020 (VCTE) 7,367 31.3% (29.2–33.4) 2.0% (1.6–2.9) 0.7% (0.5–0.9) Lee 2024, PMID 37732946
NHANES 2017–2023 (VCTE, age-adjusted) 12,199 31.9% (30.4–33.4) 2.2% (1.8–2.6) 0.8% (0.6–1.1) Kim 2025, PMID 39610192
NHANES III (ultrasound) 9,939 30% 2.3% 1.0% Sripongpun 2024, PMID 39290401
Veterans Health Administration 2010–2021 (imaging-confirmed steatosis) 341,601 77.3% of SLD 17.9% of SLD 4.8% of SLD Ochoa-Allemant 2025, PMID 40522656

The VHA proportions differ sharply from the NHANES proportions because the denominator is different (people with imaging-confirmed steatosis in care, 91.9% male) — an illustration of why SLD subcategory fractions are not portable between settings.

Outcomes across the band. In the VHA cohort, compared with MASLD, MetALD had a higher incidence of adverse liver outcomes (1.12 vs 0.61 per 100 person-years; HR 1.56, 95% CI 1.50–1.62) and all-cause mortality (HR 1.08, 1.05–1.10), and ALD higher still (adverse liver outcomes HR 2.33, 2.20–2.47; mortality HR 1.42, 1.36–1.48) — but MACE incidence was similar across all three subtypes (PMID 40522656). In UK Biobank (n=464,556), liver-cancer risk rose stepwise from MetALD (aHR 1.70, 1.37–2.09) through MASLD (1.91, 1.66–2.21) and MAFLD (2.01, 1.76–2.29) to ALD (3.16, 2.54–3.93) and MASLD-with-viral-hepatitis (22.0, 10.8–44.4) (Zeng 2025, PMID 39949980). In NHANES III with ~27 years of mortality follow-up, ALD had significantly lower overall survival than MASLD (p=0.004) but MetALD did not differ significantly (p=0.165) (Sripongpun 2024, PMID 39290401). The direction is consistent; the magnitude is not, and cohort composition explains much of the spread.

The measurement problem. MetALD is defined by a quantity — grams of alcohol per week — that is self-reported and systematically under-reported. An expert position statement recommends assessing recent and lifetime intake, using validated instruments (AUDIT-C) and objective biomarkers (phosphatidylethanol), and collateral history, and warns explicitly that heavy alcohol use itself raises blood pressure, triglycerides and glucose; diagnosing MASLD on a single metabolic criterion in someone above the weekly alcohol thresholds may therefore attribute to metabolism a disease driven by alcohol (Arab 2025, PMID 39608457). It also recommends re-assessing both exposures over time, since neither is fixed. A broader review of MetALD reaches the same conclusion — accurate quantification is the rate-limiting step for the category to function (Ayares 2025, PMID 40179033).

How large is the misclassification? It has now been measured directly. In a prospective Danish cohort of 2,924 at-risk individuals aged 30–75 (1,482 recruited for excessive alcohol use, 1,442 for metabolic dysfunction without excessive use), phosphatidylethanol — a direct biomarker of alcohol intake over the preceding 1–4 weeks — was compared against self-report (Torp 2025, PMID 40945520):

Finding Value
Median PEth, alcohol group vs metabolic group 172 ng/mL (IQR 45–434) vs 11 ng/mL (5–37)
Correlation with self-reported 3-month intake rS 0.628 (alcohol group), 0.725 (metabolic group)
Under-reported intake by PEth 39.5% of the alcohol group, 11.1% of the metabolic group
Of 1,433 participants classified as MASLD, proportion with PEth in the MetALD or ALD range (≥20 ng/mL) 559 (39.0%)
High self-reported intake but PEth <20 ng/mL (i.e. over-reporting) 0.7% and 0.1% — essentially nobody
Testing diagnostically redundant (self-report consistent with MASLD and low AUDIT-C, or self-report already in the ALD range) 812 of 2,042 with SLD (39.8%)

In this selected at-risk cohort, two-fifths of people classified as MASLD by self-report had a biomarker in the MetALD or ALD range. Misclassification was essentially one-directional — under-reporting was common and over-reporting rare. If the same pattern occurs in outcome cohorts, contamination of the MASLD comparator would tend to attenuate MetALD-versus-MASLD hepatic hazard ratios; the study does not establish that 39% applies to other cohorts or quantify their bias. The decision tree combining self-report with AUDIT-C made PEth redundant in about 40% of this cohort, concentrating testing where it changes classification. Note the funding source (Novo Nordisk Foundation) and that PEth reflects only the preceding 1–4 weeks, so it detects current, not lifetime, exposure — which is why the expert statement asks for both (PMID 39608457).

MAFLD, and why two definitions still coexist

MAFLD was proposed in 2020 by a separate expert group as a "positive" definition: steatosis plus overweight/obesity, or T2D, or ≥2 metabolic abnormalities — and, crucially, not requiring the exclusion of other liver diseases, so a patient can have MAFLD and hepatitis B simultaneously (Eslam 2020, PMID 32044314). It attracted a multi-stakeholder endorsement (Méndez-Sánchez 2022, PMID 35248211) and remains in use, particularly in Asia-Pacific literature; the APASL guidelines are written for "metabolic dysfunction-associated fatty liver disease" (Eslam 2025, PMID 40016576), and a 2024 Chinese national guideline uses MAFLD (Fan 2024, PMID 39544247).

The definitions are not interchangeable. In NHANES III (n=7,519), prevalence was NAFLD 18.5%, MAFLD 19.3%, MASLD 20.8%; 94.5% of NAFLD and 100% of MAFLD cases were also MASLD, but only 84.1% of MASLD cases were NAFLD and 92.7% were MAFLD. Over a median 26.9 years, MAFLD (aHR 1.18, 95% CI 1.04–1.33) and MASLD (1.19, 1.06–1.34) were associated with all-cause mortality but NAFLD was not — the excess sitting mainly in the NAFLD-negative/MASLD-positive subgroup (Song 2024, PMID 38293788). That is a direct demonstration that the definitional shift changes measured associations at the margin, even when overlap is ≥94%.

Is one category enough? Data-driven subtypes

The nomenclature debate has been about where to draw the boundary between MASLD, MetALD and ALD. A separate question is whether MASLD itself is one disease. Partitioning-around-medoids cluster analysis on six simple clinical variables in 1,389 individuals with obesity, applied to three independent biopsy cohorts (1,099 participants) and to UK Biobank for incident outcomes, identified two distinct types of MASLD with similar liver phenotypes at baseline but different trajectories (Raverdy 2024, PMID 39653777):

Cluster Character Trajectory
Liver-specific genetically linked rapid progression of chronic liver disease; limited cardiovascular risk
Cardiometabolic dysglycaemia, high triglycerides similar incidence of chronic liver disease, but higher cardiovascular disease and type 2 diabetes risk

The two clusters had distinct liver transcriptomic profiles (831 individuals) and distinct plasma metabolomic signatures (1,322 individuals), so the separation is not merely a re-description of the input variables. Three consequences follow. It supplies a candidate explanation for the lean-MASLD organ split — a liver-heavy, heart-light phenotype is what the liver-specific cluster looks like (lean MASLD). It is consistent with the PheWAS finding of at least seven genetically defined subtypes (genetics), while proposing a coarser and more immediately usable two-way split. And it argues that the single label MASLD, which the 2023 process worked hard to define precisely, may still be too coarse for trial design or treatment selection. The clusters are explicitly preliminary and have not been prospectively validated or used to allocate therapy.

What the renaming did and did not change

Changed Did not change
The name, and the requirement for a positive metabolic criterion The histological spectrum: steatosis → steatohepatitis → fibrosis → cirrhosis
Created MetALD as a named, countable category The primacy of fibrosis stage as the outcome-relevant variable (Angulo 2015, PMID 25935633; Hagström 2017, PMID 28803953)
Created cryptogenic SLD for the metabolically silent remainder Non-invasive test thresholds — FIB-4 and ELF performed identically in NAFLD and MASLD (PMID 38286339)
Made the diagnosis expressible without a negation The evidence base, which was generated under NAFLD/NASH criteria

AASLD published its NAFLD Practice Guidance in 2023 (Rinella 2023, PMID 36727674) shortly before the nomenclature statement, then issued a companion commentary stating that MASLD and MASH can be read interchangeably for NAFLD and NASH throughout that document (Kanwal 2024, PMID 38445559). EASL's 2024 clinical practice guidelines were written natively in the new vocabulary (EASL-EASD-EASO 2024, PMID 38851997). A 2025 Delphi exercise across 61 guideline documents published 2018–January 2025 built consensus recommendations spanning the vocabulary change, reporting >90% agreement on all final statements after four rounds (Younossi 2025, PMID 40222485).

Terminology used on these pages

  • MASLD/MASH for the disease as currently defined and for statements about it today.
  • NAFLD/NASH when describing what a specific study enrolled, measured or reported. A 2015 paired-biopsy cohort studied NAFLD; saying so is more accurate than back-dating the new label onto it.
  • SLD when the referent is the umbrella including alcohol-related disease.
  • MAFLD only when a cited source used that definition, since its population differs.

Open questions

  • How much of "MASLD" is actually MetALD or ALD? In a prospective at-risk cohort, 39.0% of those classified as MASLD by self-report had phosphatidylethanol in the MetALD or ALD range, with under-reporting in 39.5% of the alcohol group and 11.1% of the metabolic group, and essentially no over-reporting (PMID 40945520). No published outcome cohort has been reclassified by biomarker, so every MASLD-versus-MetALD comparison in this knowledge base is biased toward the null by an unmeasured amount.
  • Should PEth enter the diagnostic definition, and at what threshold? A decision tree combining self-report with AUDIT-C made testing redundant in ~40% of patients (PMID 40945520), but the 20 ng/mL and 80/200 ng/mL cut-offs used to define under-reporting are conventions, not outcome-anchored thresholds, and no guideline currently requires the test (guidelines).
  • Is MASLD one disease or two? Unsupervised clustering on six routine variables separates a genetically-linked liver-specific type from a cardiometabolic type with the same baseline liver phenotype but different transcriptomes, metabolomes and outcome trajectories (PMID 39653777). If replicated, the 2023 definition names a category that contains at least two diseases with opposite dominant risks, which would matter more for treatment than the alcohol boundary does.
  • How much does the reclassification move measured effect sizes? Overlap is ≥94% in population samples, yet NAFLD was not associated with all-cause mortality in NHANES III while MASLD was (PMID 38293788), and MASLD carried slightly higher mortality than NAFLD in a second analysis attributed to cardiometabolic burden (PMID 38286339). Re-analysis of existing cohorts under both definitions is designable today and largely has not been done at scale.
  • Is a single cardiometabolic criterion enough? One criterion suffices for diagnosis, and 95% of one tertiary cohort qualified on BMI alone (PMID 38286339). Whether requiring ≥2 criteria would improve prognostic discrimination has not been tested prospectively.
  • Can MetALD be measured reliably enough to be a useful category? It is defined by self-reported grams of alcohol, and the position statement recommending biomarker confirmation (PMID 39608457) implies that current cohort estimates of MetALD prevalence and outcome are exposure-misclassified by an unmeasured amount.
  • Does removing "fatty" and "nonalcoholic" actually reduce stigma? Stigma was a stated motivation and was measured in the panel (61%/66%), not in patients experiencing the diagnosis; whether the new name changes patient experience or clinician behaviour is an unanswered empirical question. See patient experience and advocacy.

References

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