NAFLD / MASLD History of Treatment Over Decades

The 1980s: Naming a Disease Nobody Knew How to Treat

The modern clinical story of NAFLD begins with a 1980 Mayo Clinic case series by Ludwig and colleagues, who described 20 patients with histologic liver changes resembling alcoholic hepatitis in people who consumed little or no alcohol. [1] That paper coined the term "nonalcoholic steatohepatitis" and set off four decades of research into a condition that had no approved therapy for most of its recognized existence.

Why Early Treatment Was Purely Supportive

Through the 1980s, clinicians had no controlled trial data to guide pharmacologic choices. The working assumption was that NAFLD was a metabolic sequela of obesity and insulin resistance, so the treatment approach was straightforward: reduce caloric intake, increase physical activity, and address comorbidities such as type 2 diabetes and hypertension. No guideline-body had yet issued formal recommendations specific to NAFLD, and biopsy was rarely performed outside academic centers.

The disease was considered benign by many practitioners of that era. Autopsy studies published through the late 1980s would gradually correct that assumption by documenting that a subset of patients with steatohepatitis progressed to cirrhosis and hepatocellular carcinoma at rates previously underappreciated. [2]

The Insulin-Resistance Hypothesis Takes Shape

By the end of the decade, researchers had begun framing NAFLD as a hepatic manifestation of what would later be called metabolic syndrome. This framing, though not yet formalized, pointed toward insulin sensitization as a logical therapeutic target, a line of thinking that would dominate trial design for the next 20 years. [3]

The 1990s: Pilot Trials and the First Pharmacologic Attempts

The 1990s produced small, often uncontrolled trials testing agents that were already available for other metabolic conditions. Ursodeoxycholic acid (UDCA), metformin, and various antioxidants were each studied without consistent evidence of histologic benefit. [4]

Ursodeoxycholic Acid: Early Hope, Later Disappointment

UDCA attracted early interest because of its established role in primary biliary cholangitis. Open-label series from France and North America reported biochemical improvements in alanine aminotransferase (ALT) with 13 to 15 mg/kg/day dosing. A subsequent randomized controlled trial published in Gastroenterology in 2004 (N=166) found no difference in histologic outcome between UDCA and placebo at 2 years, effectively ending enthusiasm for the drug in NASH. [5]

Metformin: Logical but Insufficient

Metformin was studied on the hypothesis that reducing hepatic glucose output and improving peripheral insulin sensitivity would secondarily reduce liver fat. The TONIC trial (N=173), which enrolled pediatric patients with NAFLD, showed that metformin did not produce sustained ALT normalization or histologic improvement compared with placebo over 96 weeks. [6] Adult studies produced similarly underwhelming results, and metformin has never been recommended by AASLD or EASL specifically for NASH histology.

The 2000s: Thiazolidinediones and Vitamin E Emerge

The 2000s brought the first rigorously designed randomized controlled trials in NASH. Two drug classes dominated the conversation: thiazolidinediones (TZDs) and antioxidants, particularly vitamin E.

Pioglitazone: The First Agent with Convincing Phase 2 Data

Pioglitazone activates peroxisome proliferator-activated receptor gamma (PPARγ), improving hepatic and peripheral insulin sensitivity. A pilot trial by Belfort and colleagues published in the New England Journal of Medicine in 2006 (N=55) showed significant reductions in liver fat by MR spectroscopy and improvements in lobular inflammation with 45 mg/day of pioglitazone over 6 months. [7]

That result led directly to the NIH-funded PIVENS trial (N=247), which compared pioglitazone 30 mg/day, vitamin E 800 IU/day, and placebo over 96 weeks in non-diabetic adults with biopsy-proven NASH. Pioglitazone achieved NASH resolution in 34% of participants versus 19% for placebo (P<0.001), but it did not reach the pre-specified primary endpoint of a 2-point improvement in the NAS score with at least 1-point improvement in ballooning. [8]

Vitamin E: Effective in Non-Diabetics, Controversial Elsewhere

In the same PIVENS trial, vitamin E 800 IU/day achieved the primary endpoint with 43% of patients showing the composite histologic improvement compared with 19% on placebo (P<0.001). [8] This was the first time any agent produced statistically significant histologic benefit in a well-powered NASH trial. AASLD incorporated these data into its 2012 NAFLD practice guidance, recommending vitamin E for non-diabetic adults with biopsy-proven NASH.

The enthusiasm was tempered by two concerns. First, a meta-analysis in the Annals of Internal Medicine suggested that high-dose vitamin E supplementation (400 IU/day or more) might be associated with a small increase in all-cause mortality, though absolute risk differences were modest. [9] Second, vitamin E showed no benefit in diabetic patients with NASH in subsequent analyses, which limited its clinical applicability given that type 2 diabetes affects the majority of patients with advanced NASH.

The 2010s: Lifestyle Quantification and the GLP-1 Era Begins

Defining the Weight-Loss Threshold

The 2010s produced quantitative data on how much weight loss was needed to produce histologic improvement. A 2015 study published in Hepatology (N=293) showed that patients achieving 10% or more total body weight loss had NASH resolution in 90% of cases and fibrosis improvement in 45%, compared with negligible improvement in those who lost less than 5%. [10] This established 10% weight loss as a clinically meaningful target that AASLD and EASL subsequently referenced in their guidance documents.

The LEAN Trial: GLP-1 Agonists Enter NASH

The LEAN trial, published in The Lancet in 2016, was the first randomized controlled trial of a GLP-1 receptor agonist specifically in patients with biopsy-proven NASH. Liraglutide 1.8 mg/day for 48 weeks (N=52) produced NASH resolution in 39% of patients versus 9% on placebo (P=0.019), with no worsening of fibrosis in 71% of the liraglutide group compared with 30% on placebo. [11] The trial was small, but its signal was strong enough to launch a generation of larger GLP-1 trials.

Obeticholic Acid: Fibrosis Benefit, Regulatory Setback

Obeticholic acid (OCA), a farnesoid X receptor (FXR) agonist, generated significant industry interest after the FLINT trial (N=283) demonstrated improvements in NAS score and fibrosis stage compared with placebo. [12] The Phase 3 REGENERATE trial (N=931) showed statistically significant fibrosis improvement at the 25 mg dose at 18 months. Despite these results, the FDA declined to grant accelerated approval in 2020 and again withheld full approval in 2023 citing concerns about the magnitude of clinical benefit relative to risk, including pruritus affecting up to 51% of patients at the 25 mg dose and a potential cardiovascular signal in patients with cirrhosis. [13]

The 2020s: Nomenclature Reform and the First Approval

Why NAFLD Became MASLD in 2023

In 2023, a multinational Delphi consensus involving the American Association for the Study of Liver Diseases (AASLD), the European Association for the Study of the Liver (EASL), and the Latin American Association for the Study of the Liver (ALEH) formally replaced "NAFLD" with "MASLD" (metabolic dysfunction-associated steatotic liver disease) and "NASH" with "MASH" (metabolic dysfunction-associated steatohepatitis). [14] The rationale was two-fold: the old "nonalcoholic" framing defined the disease by exclusion rather than by its metabolic drivers, and stigma associated with the word "fatty" was considered a barrier to patient engagement.

The new nomenclature introduced five cardiometabolic criteria. A patient qualifies for MASLD if hepatic steatosis is present alongside at least one of: BMI above 25 kg/m2 (or above 23 kg/m2 in Asian populations), fasting glucose at or above 100 mg/dL, blood pressure at or above 130/85 mmHg, triglycerides at or above 150 mg/dL, or HDL cholesterol below 40 mg/dL in men (below 50 mg/dL in women). [14] This cardiometabolic framing aligned the condition with its actual pathophysiology for the first time.

Semaglutide in NASH: ESSENCE Trial

The ESSENCE Phase 3 trial, published in the New England Journal of Medicine in 2024, evaluated subcutaneous semaglutide 2.4 mg weekly in 800 patients with biopsy-proven MASH and fibrosis stages F2 or F3. At 72 weeks, MASH resolution occurred in 62.9% of the semaglutide group versus 34.3% on placebo (P<0.001), and fibrosis improvement by at least one stage occurred in 37.0% versus 22.4% (P<0.001). [15] These results represented the largest histologic effect size seen in any NASH/MASH trial to that point.

Resmetirom: The First FDA-Approved Drug for MASH

Resmetirom (brand name Rezdiffra), a thyroid hormone receptor beta (THR-β) selective agonist, received FDA approval on March 14, 2024, for adults with non-cirrhotic MASH and moderate to advanced fibrosis (F2 or F3). [16] The approval was based on the MAESTRO-NASH Phase 3 trial (N=966), in which the 100 mg/day dose achieved MASH resolution without worsening fibrosis in 29.9% of patients and fibrosis improvement of at least one stage in 25.9% at 52 weeks, versus 9.7% and 14.2% for placebo respectively (both P<0.001). [17]

Resmetirom is dosed orally once daily. The 80 mg dose is used in patients with moderate hepatic impairment or those on certain concomitant medications. THR-β selectivity was designed to concentrate the metabolic benefits of thyroid hormone agonism in the liver while avoiding cardiac and bone effects seen with non-selective agonists. [17]

The table below places the four-decade arc of MASH pharmacology in context. Each row represents a class that reached Phase 2 or Phase 3 evaluation, along with its regulatory outcome.

| Drug Class | Agent | Key Trial | Histologic Endpoint Met | Regulatory Status (U.S.) | |---|---|---|---|---| | Antioxidant | Vitamin E 800 IU/day | PIVENS (2010) | Yes (non-diabetics only) | Off-label; AASLD-recommended for select patients | | TZD | Pioglitazone 30 mg | PIVENS (2010) | Partial | Off-label; used in diabetic MASH | | FXR agonist | Obeticholic acid | REGENERATE | Fibrosis (not NASH resolution) | Not approved | | GLP-1 agonist | Liraglutide 1.8 mg | LEAN (2016) | Yes (small N) | Not approved for MASH | | GLP-1 agonist | Semaglutide 2.4 mg | ESSENCE (2024) | Yes (62.9% resolution) | Not yet approved specifically for MASH | | THR-β agonist | Resmetirom 80/100 mg | MAESTRO-NASH (2024) | Yes | FDA-approved March 2024 |

Lifestyle Therapy: Four Decades of Consistent Evidence

Lifestyle modification has been the only intervention consistently recommended across every major NAFLD/MASLD guideline from the 1990s onward. The evidence base has grown progressively more specific about dose and type.

Caloric Restriction and Weight Loss Targets

A 2023 AASLD practice guidance document states: "Weight loss of at least 3 to 5% improves steatosis, but greater weight loss (7 to 10%) is generally needed to improve necroinflammation and potentially fibrosis." [18] This language directly reflects the Hepatology 2015 dataset cited earlier [10] and has remained stable across guideline iterations.

Caloric deficits of 500 to 1,000 kcal/day producing 0.5 to 1 kg/week of weight loss are the standard recommendation. Very low-calorie diets (<800 kcal/day) produce faster initial weight loss but carry higher dropout rates and have not demonstrated superior long-term histologic outcomes in controlled comparisons.

Exercise Independent of Weight Loss

Aerobic exercise reduces liver fat even without clinically meaningful weight loss. A meta-analysis of 12 randomized trials published in the Journal of Hepatology (2012) found that structured aerobic exercise reduced liver fat by approximately 3 to 4 absolute percentage points versus control groups, independent of changes in body weight. [19] Resistance training produces similar hepatic fat reductions. Current EASL guidelines recommend at least 150 to 200 minutes per week of moderate-intensity aerobic activity. [20]

Mediterranean Diet as the Preferred Dietary Pattern

No dietary pattern has stronger evidence in MASLD than the Mediterranean diet. A randomized trial (N=278) showed that Mediterranean diet adherence for 6 months reduced liver fat content measured by MRI-PDFF by 29% compared with a low-fat diet control group, independent of caloric intake differences. [21] AASLD guidelines list the Mediterranean diet as the preferred dietary pattern for patients with MASLD. [18]

The Pediatric Dimension

NAFLD in children was first formally characterized in the 1990s, and it differs histologically from adult disease. Pediatric NAFLD more commonly shows zone 1 (periportal) steatosis and fibrosis rather than the zone 3 (centrilobular) pattern predominant in adults. [22]

The TONIC trial (N=173) remains the largest pediatric NASH pharmacotherapy trial. Neither metformin nor vitamin E at 400 IU/day produced sustained ALT normalization versus placebo at 96 weeks. [6] No pharmacologic agent has FDA approval for pediatric NASH/MASH as of early 2025, and management remains centered on lifestyle modification in children and adolescents.

Cardiovascular Risk: The Underappreciated Priority

From the earliest recognition of NAFLD, cardiovascular disease has been its leading cause of death, not liver-related mortality. A prospective cohort study (N=458) published in Hepatology showed that cardiovascular events accounted for 25% of deaths in NAFLD patients over a median follow-up of 13.7 years, compared with 13% from liver-related causes. [23]

This cardiovascular burden has shaped treatment priorities. Statins, long avoided in NAFLD patients due to concerns about hepatotoxicity, have been endorsed by AASLD since 2012 as safe and appropriate for cardiovascular risk reduction in patients with NAFLD, including those with elevated transaminases. [18] No randomized trial has demonstrated that statin use improves NASH histology, but the cardiovascular mortality data make lipid management non-negotiable in standard care.