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Nonalcoholic Fatty Liver Disease (NAFLD/MASLD): Overview, Diagnosis, and Treatment

Nonalcoholic fatty liver disease, now increasingly called MASLD, affects roughly a third of the world's adult population according to recent meta-analyses — yet most people don't know they have it, since the disease is typically silent for years. We explain how it's diagnosed, why it progresses to more serious liver inflammation (NASH/MASH) in some patients, and why weight loss remains the first-line treatment.

Redakcja VitMode — Badania i biomarkerythe VitMode editorial team, no individual bylinesPublished13 min read
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Redakcja VitMode — Badania i biomarkery — the VitMode editorial team, no individual bylines
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Prepared from primary sources: clinical trials, meta-analyses and guidelines. We describe study findings separately from our interpretation.
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Cited PubMed papers are automatically checked for a matching identifier, title and publication year.
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Table of contents

A disease affecting one in three adults that rarely causes symptoms

Nonalcoholic fatty liver disease (NAFLD) is the accumulation of excess fat in liver cells in people who don't drink alcohol in amounts that could account for it on their own (conventionally, under 20 g/day for women and 30 g/day for men), and in whom other causes of fatty liver have been ruled out. In 2023, international liver societies proposed renaming it MASLD (metabolic dysfunction-associated steatotic liver disease), better reflecting its true underlying driver and requiring at least one cardiometabolic risk factor (e.g., obesity, insulin resistance, hypertension, or dyslipidemia) for diagnosis.

The scale of the problem is larger than it might seem. A large meta-analysis published in Hepatology in 2023, covering data from 1990–2019, estimated the global prevalence of NAFLD at 30.05% of the adult population (95% CI: 27.88–32.32%) — with a clear upward trend across recent decades, closely tied to rising rates of obesity and type 2 diabetes worldwide.

From simple steatosis to NASH/MASH — a disease spectrum

NAFLD/MASLD isn't a single, uniform condition — it's a spectrum, with simple steatosis (fat accumulation in liver cells without accompanying inflammation) at one end, and steatohepatitis — formerly called NASH, now MASH (metabolic dysfunction-associated steatohepatitis) — at the other, where cell damage and inflammation join the fat accumulation itself. This distinction matters a great deal for prognosis: simple steatosis on its own usually follows a mild, slowly progressing course, while NASH/MASH carries a real risk of progressing to fibrosis, cirrhosis, and in some cases hepatocellular carcinoma.

Not everyone with simple steatosis will develop NASH, and not everyone with NASH will develop cirrhosis — but determining where a given patient sits on this spectrum is essential for deciding on further management and follow-up frequency. That's why modern NAFLD/MASLD diagnosis increasingly focuses not just on confirming the presence of fat in the liver (relatively easy to do), but on assessing the degree of fibrosis, which correlates best with long-term prognosis.

How NAFLD/MASLD is actually diagnosed

In practice, this means a primary care doctor can make an initial estimate of advanced fibrosis risk in a patient with suspected NAFLD/MASLD (e.g., steatosis incidentally found on an abdominal ultrasound, or elevated liver enzymes) using a simple calculation from routine blood tests, without needing to immediately refer every patient for an invasive biopsy. Liver biopsy remains the reference method for ambiguous cases or when another, coexisting liver disease is suspected, but it's no longer the first diagnostic step.

Who is at risk

Why weight loss is the first-line treatment

Unlike many other chronic liver diseases, NAFLD/MASLD has a well-documented, effective non-pharmacological intervention — weight loss. The relationship between the amount of weight lost and the degree of improvement in the liver is clearly dose-dependent, making it one of the few chronic diseases where a specific, measurable weight target translates directly into hard liver-tissue endpoints rather than just intermediate markers.

Lifestyle modification — combining a calorie deficit, regular physical activity, and improved diet quality — remains, as AASLD guidance emphasizes, the cornerstone of NAFLD/MASLD/MASH management, even in the era of new pharmacological treatments. That doesn't mean pharmacotherapy is irrelevant — for patients with more advanced disease it's a meaningful addition, not a replacement for lifestyle change.

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New pharmacological options — cautious optimism

For many years, NAFLD/MASLD remained a disease without an approved pharmacological treatment aimed directly at the liver — lifestyle change and management of coexisting conditions remained the foundation. That's changing: resmetirom became the first FDA-approved drug specifically for patients with MASH and F2–F3 fibrosis, and semaglutide (better known as a drug used for type 2 diabetes and weight loss) has shown a favorable effect on liver histology in clinical trials of patients with moderate-to-advanced fibrosis.

When NAFLD/MASLD becomes a serious problem

In some patients with untreated or poorly controlled MASH, the disease progresses through successive stages of fibrosis to cirrhosis — a state in which normal liver tissue is permanently replaced by scar tissue, impairing organ function. In recent years, NAFLD/MASLD has become one of the leading causes of liver cirrhosis worldwide, overtaking viral hepatitis as the main driver in many regions. We cover the causes, stages, and symptoms of liver cirrhosis in detail in a separate article.

Summary table

QuestionShort answer
How common is it?About 30% of the world's adult population (Hepatology 2023 meta-analysis)
What's the difference between MASLD and NASH/MASH?MASLD is the fat accumulation itself; MASH is steatosis plus inflammation, with risk of progressing to fibrosis
How is fibrosis risk assessed?The FIB-4 index from routine blood tests as the first step, biopsy only for unclear cases
How much weight loss helps the liver?3–5% for improved steatosis, >10% for improved NASH and fibrosis
Is there an approved drug for MASH?Yes — resmetirom (for F2–F3 fibrosis), and semaglutide showing benefit in trials
NAFLD/MASLD at a glance

Our editorial recommendation

NAFLD/MASLD is a disease where the gap between the scale of the problem and public awareness is unusually large — it affects nearly one in three adults, yet most people with the diagnosis find out about it by accident, during tests done for a completely different reason. The good news is that, unlike many other chronic liver diseases, we have a well-documented, dose-dependent intervention here — weight loss — available to every patient regardless of access to the newest drugs.

If you suspect you have NAFLD/MASLD (for example, based on incidentally detected steatosis on ultrasound or elevated liver enzymes) or have already been diagnosed, the key step is working out with your doctor where on the disease spectrum you sit — that determines both the urgency of further workup and a realistic treatment target.

NAFLD/MASLD rarely hurts until it's already seriously advanced — which is exactly why regular check-ups and early fibrosis-risk assessment matter more here than for diseases that announce themselves through symptoms.
VitMode editorial team

Frequently asked questions

Largely the same phenomenon under a new name. In 2023, international liver societies proposed replacing the term NAFLD (nonalcoholic fatty liver disease) with MASLD (metabolic dysfunction-associated steatotic liver disease) to better reflect the disease's metabolic underpinnings and to require at least one cardiometabolic risk factor for diagnosis, rather than relying mainly on ruling out alcohol.

No. Only some patients with simple steatosis develop steatohepatitis (NASH/MASH), and only some people with NASH/MASH progress to advanced fibrosis and cirrhosis. That's why it's essential to determine where on the disease spectrum a given patient sits, rather than assuming the worst-case scenario by default.

Usually not. 2023 AASLD guidance recommends the noninvasive FIB-4 index, calculated from routine blood tests, as the first step, reserving biopsy for ambiguous cases or when another coexisting liver disease is suspected.

Losing 3–5% of body weight usually improves the steatosis itself, but improving inflammation and reversing fibrosis (in patients with more advanced disease) usually requires losing more than 10% of starting body weight — meaningfully more than the popular, moderate weight-loss targets.

Yes, and the situation is changing rapidly. Resmetirom is the first FDA-approved drug specifically for patients with MASH and F2–F3 fibrosis, and semaglutide has shown a favorable effect on liver histology in clinical trials. Pharmacological treatment complements, rather than replaces, lifestyle change.

Yes, though less often than people who are overweight. Insulin resistance, an unfavorable (visceral) fat distribution, and genetic factors can lead to NAFLD/MASLD even at a normal BMI, which is why a normal weight alone doesn't rule out the need for workup when liver test results are abnormal.

Chronic fatigue and discomfort under the right ribs, jaundice, leg swelling or increased abdominal girth, easy bruising, and persistently abnormal liver enzyme results are signals that warrant prompt medical consultation and further workup.

Choline and vitamin E have a documented, though situation-specific, effect on disease course — we cover them in detail in separate articles. No supplement, however, replaces weight loss and management of coexisting conditions as the foundation of treatment.

Sources (2)

Sources are numbered. PubMed items are automatically verified (identifier, title, year).

  1. 1Younossi ZM et al. 2023 — Hepatology (global epidemiology of NAFLD/NASH)PubMed
  2. 2Rinella ME et al. 2023 — AASLD Practice Guidance, HepatologyPubMed
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Redakcja VitMode — Badania i biomarkery

VitMode editorial team — no individual bylines; content based on primary sources

VitMode Editorial — Lab Tests and Biomarkers is the VitMode editorial team responsible for: laboratory tests, interpreting results and ageing biomarkers. The team has no individual bylines — texts are prepared by VitMode editors from primary sources (clinical trials, meta-analyses, guidelines). Every cited PubMed paper is automatically checked for a matching identifier, title and publication year. The content is educational and does not replace medical advice. Factual errors can be reported in a comment under the post or through the contact form; corrections are made by the editorial team.

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