NAFLD / MASLD Open Controversies in the Field

Why the Rename From NAFLD to MASLD Is Still Contested

The 2023 multi-society nomenclature shift replaced "non-alcoholic fatty liver disease" with "metabolic dysfunction-associated steatotic liver disease" (MASLD) and carved out a new overlap category called MetALD for patients with both metabolic risk factors and higher alcohol intake. The rename aimed to reduce stigma and align the diagnosis with its cardiometabolic roots. Not every hepatologist is satisfied, however.

The Alcohol Threshold Problem

MASLD permits up to 14 standard drinks per week in men and 7 per week in women before a patient is reclassified as MetALD or ALD. Critics argue this cutoff is arbitrary. A 2023 BMJ meta-analysis (N=836,147) found that even 10 to 15 grams of alcohol per day raised liver-related mortality by roughly 18% compared with abstinence, well within the MASLD "allowed" window [1]. The multi-society consensus published in Hepatology acknowledged the threshold was a pragmatic compromise, not an evidence-based bright line [2].

Stigma Reduction: Promise vs. Reality

The original rationale for dropping "non-alcoholic" was that the negative framing discouraged patients from discussing their condition. A 2024 survey study in the Journal of Hepatology (N=412 patients) found that 61% of participants did not know their new diagnosis name six months after the rename, suggesting the nomenclature change may not yet be reaching patients in routine clinical encounters [3].

Screening: Who Should Be Tested and How?

No major guideline, including the 2023 American Association for the Study of Liver Diseases (AASLD) guidance, recommends universal ultrasound screening for MASLD in the general population [4]. That gap is actively debated.

The Case for Targeted Screening

The AASLD 2023 Practice Guidance recommends offering non-invasive testing to patients with type 2 diabetes, obesity (BMI >30), or metabolic syndrome, but stops short of specifying a universal starting age or screening interval [4]. The European Association for the Study of the Liver (EASL) 2024 Clinical Practice Guidelines go somewhat further, recommending FIB-4 calculation in all patients with type 2 diabetes at least once as a baseline fibrosis screen [5].

The practical argument for broader screening is compelling. A population-based cohort from Sweden (N=10,568) published in Gut (2023) found that advanced fibrosis at first diagnosis was present in 14.2% of newly identified MASLD patients, most of whom had no symptoms [6]. Identifying these patients earlier could allow treatment before cirrhosis develops.

The Case Against Routine Screening

Counter-arguments center on cascade testing anxiety, the low positive predictive value of FIB-4 in lower-prevalence populations, and the absence of a proven, widely available, cost-effective intervention to offer everyone who screens positive. Before the March 2024 FDA approval of resmetirom, there was no licensed pharmacotherapy to offer a screen-detected MASH-fibrosis patient, which weakened the cost-benefit case substantially [7].

Is Liver Biopsy Still the Diagnostic Gold Standard?

Liver biopsy has been the reference standard for diagnosing MASH (metabolic dysfunction-associated steatohepatitis) and staging fibrosis for decades. In 2025, that status is genuinely contested.

Limitations of Biopsy

Biopsy carries a 0.5 to 1% risk of significant complications including bleeding and a 1-in-10,000 mortality risk [8]. Sampling error is well-documented: a landmark study in Hepatology (N=51 paired biopsies) found that two cores from the same liver disagreed on fibrosis stage in 33% of cases [9]. Given that fibrosis stage drives prognosis, that level of intra-specimen variability is clinically meaningful.

Non-Invasive Alternatives and Their Gaps

The FIB-4 index (calculated from age, AST, ALT, and platelet count) performs well at ruling out advanced fibrosis when the score is <1.30, with a negative predictive value exceeding 90% in most validation cohorts [10]. The Enhanced Liver Fibrosis (ELF) score and vibration-controlled transient elastography (VCTE, commercially FibroScan) add information but each has known failure rates in patients with BMI >40 or narrow intercostal spaces.

The FDA accepted biopsy-based endpoints for the resmetirom approval, meaning the field's regulatory framework still leans on histology [7]. AASLD's 2023 guidance states that "non-invasive tests can risk-stratify but should not replace biopsy when treatment decisions hinge on distinguishing F2 from F3 fibrosis" [4].

The three-tier approach endorsed by EASL (FIB-4 first, then elastography if indeterminate, then biopsy only if both are indeterminate and treatment decisions hang on the result) represents one resolution to this debate, but it is not yet uniformly adopted in U.S. Hepatology practices [5].

Resmetirom: What the First Approval Does and Does Not Settle

The FDA approved resmetirom (Rezdiffra, Madrigal Pharmaceuticals) on March 14, 2024, for noncirrhotic MASH with moderate-to-advanced fibrosis (F2-F3) [7]. This was the first approved pharmacotherapy specifically for MASH. The MAESTRO-NASH trial (N=966) showed that resmetirom 100 mg achieved NASH resolution without worsening fibrosis in 25.9% of patients vs. 14.2% placebo (P<0.001), and fibrosis improvement of at least one stage in 25.9% vs. 14.7% placebo [11].

What Remains Unresolved

The approval used surrogate histologic endpoints, not hard clinical outcomes like liver-related mortality or liver transplantation. The FDA granted accelerated approval, meaning Madrigal must complete the MAESTRO-NASH OUTCOMES trial to confirm cardiovascular and liver-related mortality benefit [7]. Whether surrogate histologic improvement translates to longer life is the central unanswered question.

Resmetirom also carries a boxed-warning-adjacent label discussion about drug-drug interactions via CYP2C8 and P-glycoprotein pathways. The full prescribing information lists statins as a class requiring dose adjustment when co-administered, a detail that matters in a patient population where statin use is near-universal [7].

Cost and Access Debate

At a list price of approximately $47,400 per year, resmetirom access is restricted by payer criteria that typically require biopsy-proven F2-F3 MASH. Given the biopsy debate above, this creates a circular problem: access requires biopsy, but biopsy itself is contested as a requirement for diagnosis and treatment initiation.

GLP-1 Receptor Agonists: Proven Benefit or Overhyped Hope?

Semaglutide and other GLP-1 receptor agonists reduce hepatic steatosis and liver enzymes consistently across multiple trials. The question is whether that translates to histologic MASH resolution and fibrosis regression.

The NASH Resolution Question

The SEMINAL semaglutide 0.4 mg/day phase 2 trial (N=320) showed NASH resolution in 59% of the semaglutide group vs. 17% placebo but did not show statistically significant fibrosis improvement [12]. The phase 3 ESSENCE trial of semaglutide 2.4 mg weekly in MASH patients with F2-F3 fibrosis reported interim 72-week data (N=800) in 2024 showing that NASH resolution without fibrosis worsening was achieved in 62.9% semaglutide vs. 34.3% placebo, but fibrosis improvement by at least one stage did not reach statistical significance at that interim timepoint [13]. Full 240-week outcomes data are expected in 2025.

ALT and Steatosis: Surrogate vs. Clinical Signal

GLP-1 agonists reliably reduce ALT by 20 to 40% and hepatic fat fraction by 30 to 40% on MRI-PDFF in MASLD patients [14]. These are meaningful signals but not yet proven surrogates for fibrosis outcomes. The AASLD has not yet endorsed GLP-1 agonists as first-line MASH-specific therapy, though the 2023 guidance notes their use is appropriate for patients with comorbid type 2 diabetes or obesity [4].

Combination Therapy Horizon

Trials combining resmetirom with semaglutide or tirzepatide are underway. The theoretical rationale is additive: resmetirom targets hepatic thyroid hormone receptor-beta to reduce lipotoxicity, while GLP-1 agonists reduce caloric intake and hepatic fat delivery. Whether the combination improves histologic outcomes more than either agent alone remains an open empirical question.

The Fibrosis Staging Controversy: Does Grade of Steatosis Matter?

Most hepatologists agree that fibrosis stage, not degree of steatosis, is the primary determinant of liver-related mortality in MASLD. A landmark longitudinal study published in Hepatology (N=411, follow-up median 12.6 years) found that each one-unit increase in fibrosis stage raised liver-related mortality by approximately 2-fold, while neither steatosis grade nor lobular inflammation independently predicted mortality after adjusting for fibrosis [15].

Steatosis Still Has Cardiovascular Implications

The controversy is that steatosis grade does correlate with cardiovascular risk independently of fibrosis. A 2023 JAMA Network Open analysis (N=5,765) found that hepatic steatosis on ultrasound was associated with a 22% higher 10-year cardiovascular event rate even after adjusting for metabolic risk factors [16]. For cardiologists co-managing these patients, steatosis reduction may matter even when fibrosis is mild.

NAFLD Activity Score (NAS) vs. Steatosis-Activity-Fibrosis (SAF) Score

Pathologists do not uniformly use the same scoring system. The NAS (0 to 8) developed by the NASH Clinical Research Network and the SAF score used more commonly in Europe weight histologic features differently. A 2021 Journal of Hepatology paper showed that 23% of patients classified as NASH by NAS criteria were not classified as MASH by SAF, and vice versa in 11% [17]. This discordance affects trial enrollment, drug approval endpoints, and clinical communication.

Dietary and Lifestyle Controversies: How Much Weight Loss Is Enough?

A 7 to 10% reduction in body weight consistently improves steatosis; 10% or more is generally required for histologic MASH resolution in most cohorts [18]. The AASLD 2023 guidance states that "weight loss of at least 10% is associated with NASH resolution in the majority of patients who achieve it" [4]. Getting there is the problem.

Very Low Calorie Diets vs. Mediterranean Diet

Both produce comparable short-term steatosis reduction, but adherence beyond 12 months favors the Mediterranean diet pattern. A randomized trial published in Gut (N=294, 18 months) found that the Mediterranean diet reduced liver fat by 38% vs. 23% for a low-fat comparator, with better 12-month retention [19]. Ketogenic and very low carbohydrate diets reduce hepatic fat rapidly but carry a theoretical risk of worsening fibrosis through free fatty acid mobilization, a concern raised in animal models that has not been confirmed in large human RCTs [20].

Exercise: Aerobic vs. Resistance Training

Both aerobic and resistance exercise reduce hepatic steatosis independently of weight loss. A 2023 Cochrane systematic review (11 RCTs, N=781) found no significant difference between aerobic and resistance training for liver fat reduction (standardized mean difference 0.08, 95% CI -0.19 to 0.36), suggesting either modality is acceptable and the choice should follow patient preference [21].

Cardiovascular Risk Management: Underappreciated and Under-Treated

Cardiovascular disease, not liver failure, is the leading cause of death in patients with MASLD/MASH who have not yet developed cirrhosis [22]. Despite this, a 2022 cohort study in JAMA Internal Medicine (N=18,240 NAFLD patients) found that only 38% of patients meeting ATP III criteria for statin therapy were actually receiving a statin at the time of their liver disease diagnosis [23].

Statins and the Liver Safety Myth

Fear of hepatotoxicity drives statin under-prescription in MASLD patients. This fear is largely unfounded. A 2019 Cochrane review (N=3,700 participants across 12 trials) found no significant elevation in serious hepatic adverse events with statin use in patients with baseline elevated transaminases due to NAFLD [24]. Both AASLD and EASL guidelines explicitly state that statins are safe and should not be withheld in MASLD patients with cardiovascular indications [4, 5].

Pediatric MASLD: A Growing and Under-Studied Population

MASLD in children and adolescents is increasing in parallel with pediatric obesity rates. A CDC-linked analysis (N=9,647, ages 2 to 19) estimated that 9.6% of U.S. Children have hepatic steatosis on ultrasound-based criteria [25]. The pediatric population presents unique controversies.

Different Histology, Different Disease?

Pediatric MASH shows a "zone 1" (periportal) pattern of injury, compared with the "zone 3" (centrilobular) adult pattern. A 2015 Hepatology paper (N=176 pediatric biopsies) established that this histologic difference is real and not explained by disease severity or BMI [26]. Whether the same fibrosis staging systems and drug endpoints used in adults apply to children is unresolved, and resmetirom's approval does not extend to patients under 18.