MASLD and MASH: Why Fatty Liver Disease Was Renamed

In June 2023, a panel convened by the American Association for the Study of Liver Diseases, the European Association for the Study of the Liver, and the Latin American association ALEH retired two of hepatology's most familiar labels. Nonalcoholic fatty liver disease (NAFLD) became metabolic dysfunction-associated steatotic liver disease (MASLD), and nonalcoholic steatohepatitis (NASH) became metabolic dysfunction-associated steatohepatitis (MASH). The change was not cosmetic: it replaced a definition built on what the disease is not with one built on what it is, and it created a formal middle category for livers with both metabolic and alcohol-related drivers. The consensus was published in the journals Hepatology and Journal of Hepatology.

One umbrella, several rooms

The new framework starts with a broad term, steatotic liver disease (SLD), meaning fat accumulation in the liver from any cause. Underneath it sit the specific diagnoses. MASLD applies when a person has hepatic steatosis plus at least one of five cardiometabolic risk factors: overweight or increased waist circumference, elevated fasting glucose or type 2 diabetes, raised blood pressure, high triglycerides, or low HDL cholesterol, each defined by a threshold or by being on treatment for that condition. MASH is the more active, inflammatory form with liver-cell injury that can progress to fibrosis and cirrhosis. A residual category, cryptogenic SLD, covers steatosis with no identifiable metabolic or alcohol driver.

The structural shift is that MASLD is a diagnosis of inclusion. The old NAFLD label required first excluding significant alcohol intake and other causes, so the name told you what a patient did not have. According to the multisociety statement, a person now qualifies by meeting positive criteria, and MASLD can coexist with other liver diseases rather than being mutually exclusive with them.

The new dividing line: MetALD

The most clinically consequential addition is MetALD, short for metabolic and alcohol-related liver disease. It names something clinicians see constantly but had no clean box for: people who meet MASLD criteria and also drink more than a modest amount. The consensus set the overlap zone at roughly 20 to 50 grams of alcohol per day for women and 30 to 60 grams per day for men (about 140 to 350 and 210 to 420 grams per week). Below that range with cardiometabolic risk, the label stays MASLD; above it, the disease is considered predominantly alcohol-related.

MetALD matters because the two drivers are not additive footnotes. Alcohol and metabolic dysfunction can each accelerate fibrosis, and folding these patients into either pure category obscured that dual burden in trials and clinics. Naming the overlap makes it a study-able entity.

Why change a name at all

Two arguments drove the vote. The first was stigma. In the surveys, most panelists judged "fatty" to be stigmatizing, and a majority objected to defining a disease by "nonalcoholic," language that can feel accusatory to patients and trivializing to the condition. The second was accuracy. Metabolic dysfunction, rooted in insulin resistance, is the actual biology; a name anchored to that biology communicates cause rather than absence.

This was a structured process, not a hallway decision. The panel used a modified Delphi method: 236 participants from 56 countries, four rounds of surveys, and a supermajority threshold of 67% to declare agreement, as reported in the published consensus. That rigor is part of why professional societies and journals adopted the terms quickly.

How to read a nomenclature change critically

A renaming is a scientific claim about how a disease should be carved up, and it deserves the same scrutiny as any other claim. A few questions travel well.

Who decided, and how?

Consensus is a method with known limits. Delphi panels reduce the loudest-voice problem, but a 67% supermajority also means a sizable minority of experts may have disagreed on specific points. Ask whether criteria were validated against patient outcomes or settled by vote. Here, the categories were defined by expert agreement and are now being tested against real cohorts.

Does the new label change who gets diagnosed?

Studies comparing NAFLD and MASLD populations find heavy overlap, with most former NAFLD patients also meeting MASLD criteria, yet the two are not identical. When a definition shifts even slightly, prevalence figures, trial eligibility, and the interpretation of older research can move with it. Continuity of evidence is a legitimate concern the field is actively tracking.

What does it change for patients?

Often, a name is just a name. The value of MASLD is that its criteria point toward action: the same cardiometabolic factors that define it, weight, glucose, blood pressure, and lipids, are the levers a person and their clinician can work on. That is the practical test of any relabeling. Does it sharpen what to do next, or only what to call it?

For readers, the honest read is that this change is well-motivated and well-documented, and still maturing as researchers confirm that the new boxes predict outcomes better than the old ones did. This article is educational and not medical advice; anyone with questions about liver test results should discuss them with their own clinician.