The liver is the body’s largest internal organ and performs hundreds of functions, including:

• processing nutrients
• regulating blood glucose
• metabolizing fats and proteins
• producing bile
• processing medications and toxins
• producing important blood proteins
• storing glycogen, vitamins and minerals
• participating in immune and metabolic regulation

Under normal circumstances, the liver contains some fat. However, when fat accumulation becomes excessive, it is considered hepatic steatosis.

Fat accumulation itself does not necessarily mean that the liver is permanently damaged. Some people have simple steatosis with little inflammation or fibrosis. Others develop inflammation and hepatocellular injury, followed by scar formation.

A simplified disease pathway is:

Liver fat → inflammation → liver-cell injury → fibrosis → advanced fibrosis → cirrhosis → liver failure and/or liver cancer

Not everyone progresses through all these stages.

Fatty liver disease can broadly be divided according to its underlying cause.

Major categories include:

1. Metabolic dysfunction-associated steatotic liver disease (MASLD)
2. Alcohol-associated liver disease (ALD)
3. Metabolic dysfunction-associated steatohepatitis (MASH)
4. Alcohol-associated steatohepatitis
5. Steatotic liver disease caused by medications
6. Steatotic liver disease associated with nutritional disorders
7. Other secondary causes of hepatic steatosis

The distinction between metabolic and alcohol-associated disease is clinically important because the underlying causes and treatment strategies can differ.

Metabolic dysfunction-associated steatotic liver disease (MASLD) is the major metabolic form of fatty liver disease.

It is associated with metabolic risk factors such as:

• overweight or obesity
• insulin resistance
• type 2 diabetes
• high triglycerides
• abnormal cholesterol
• high blood pressure
• metabolic syndrome
• central or abdominal obesity

NIDDK identifies obesity, insulin resistance/type 2 diabetes, abnormal blood lipids and metabolic syndrome among the important risk factors for MASLD.

MASLD does not simply mean that someone is overweight. People with a normal body weight can also develop metabolic fatty liver disease, particularly when they have insulin resistance, diabetes, abnormal lipid levels or genetic susceptibility.

Metabolic dysfunction-associated steatohepatitis (MASH) represents a more serious form of MASLD.

In MASH, the liver contains excess fat plus inflammation and liver-cell injury.

MASH can progressively produce:

Inflammation → fibrosis → cirrhosis

MASH is therefore substantially more clinically important than uncomplicated hepatic steatosis.

The older term NASH (non-alcoholic steatohepatitis) remains widely encountered in medical literature, clinical records and drug approvals. MASH and NASH refer essentially to the same disease entity under the newer terminology.

Fatty liver disease has become a major global public-health problem.

The European Association for the Study of the Liver has cited estimates that MASLD affects approximately 38% of the global adult population, with approximately 13% of children and adolescents affected.

The increasing prevalence has been associated with the worldwide growth of:

• obesity
• type 2 diabetes
• sedentary lifestyles
• metabolic syndrome
• energy-dense diets

The actual prevalence varies considerably between countries and populations because diagnostic definitions, imaging methods and study populations differ.

Fat accumulates in the liver when the balance between fat delivery, synthesis, oxidation and export becomes disrupted.

In metabolic fatty liver disease, several processes may contribute simultaneously.

These include:

• increased delivery of fatty acids to the liver
• increased production of fat within the liver
• impaired fatty-acid oxidation
• altered lipid export
• insulin resistance
• metabolic inflammation

The disease is therefore more complex than simply “eating too much fat.”

Dietary patterns, excess calories, insulin resistance, genetics, physical inactivity and metabolic health all contribute.

Excess body weight is one of the strongest risk factors for MASLD.

Abdominal or visceral fat is particularly important because visceral adipose tissue is metabolically active and contributes to insulin resistance and abnormal fatty-acid metabolism.

Type 2 diabetes

Type 2 diabetes is strongly associated with MASLD and MASH.

Insulin resistance can increase the movement of fatty acids into the liver and alter hepatic glucose and lipid metabolism.

People with diabetes are also more likely to develop progressive fibrosis.

Insulin resistance

Insulin resistance occurs when tissues respond less effectively to insulin.

The pancreas may initially compensate by producing more insulin.

Over time, insulin resistance can contribute to:

• elevated blood glucose
• increased liver fat
• increased triglycerides
• metabolic syndrome
• type 2 diabetes

Dyslipidemia

Abnormal blood lipids, particularly elevated triglycerides and certain cholesterol abnormalities, are associated with fatty liver disease.

Metabolic syndrome

Metabolic syndrome is a cluster of conditions involving combinations of:

• abdominal obesity
• high blood pressure
• abnormal blood lipids
• elevated blood glucose
• insulin resistance

The presence of multiple metabolic abnormalities increases the likelihood of MASLD and progressive liver disease.

Diet

Dietary patterns associated with excessive calorie intake, high consumption of added sugars and highly processed foods can contribute to metabolic fatty liver disease.

Sugar-sweetened beverages are particularly relevant because they can contribute substantial quantities of rapidly available calories.

However, there is no single “fatty liver food.”

The overall dietary pattern, calorie balance and metabolic health are more important than one isolated food.

Physical inactivity

Low levels of physical activity can contribute to:

• obesity
• insulin resistance
• impaired metabolic health
• increased liver fat

Physical activity can improve metabolic health even when substantial weight loss does not occur.

Genetics

Genetic variation influences an individual’s susceptibility to liver fat accumulation and progression to MASH and fibrosis.

Important genetic variants studied in fatty liver disease include variants affecting proteins involved in lipid metabolism, such as PNPLA3 and TM6SF2.

Genetic susceptibility helps explain why some individuals develop severe liver disease despite having similar body weight and metabolic profiles as others.

Alcohol is an important cause of hepatic steatosis.

Regular excessive alcohol consumption can cause:

Alcohol-associated fatty liver → alcohol-associated hepatitis → fibrosis → cirrhosis

The amount and pattern of alcohol consumption, genetics, sex, nutritional status and other health factors influence individual risk.

Alcohol-related and metabolic fatty liver disease can also coexist.

Therefore, alcohol history is an important component of evaluating a person with hepatic steatosis. NIDDK specifically notes that clinicians assess alcohol intake to distinguish alcohol-associated liver disease from metabolic fatty liver disease.

Not all fatty liver is caused by obesity, diabetes or alcohol.

Other causes include:

• certain medications
• rapid weight loss
• severe malnutrition
• prolonged starvation
• some inherited metabolic disorders
• lipodystrophy
• certain endocrine disorders
• some gastrointestinal conditions

Medications and other secondary causes therefore need to be considered when the clinical picture does not fit typical MASLD.

The pathogenesis of MASLD is complex and multifactorial.

A simplified model begins with metabolic dysfunction and insulin resistance.

Insulin resistance can increase the amount of free fatty acids reaching the liver.

At the same time, hepatic fat synthesis may increase and the liver’s ability to appropriately process and export lipids may become altered.

Accumulated lipids and associated metabolic stress can contribute to:

• oxidative stress
• mitochondrial dysfunction
• cellular stress
• inflammatory signaling
• hepatocyte injury

Persistent injury activates hepatic stellate cells and other pathways involved in tissue repair.

The resulting excessive deposition of extracellular matrix produces fibrosis.

Fatty liver disease is best understood as a spectrum rather than a single condition.

Stage 1: Simple steatosis

Fat accumulates in the liver without substantial inflammation or injury.

This may remain stable for many years.

Stage 2: Steatohepatitis

Fat accumulation is accompanied by inflammation and hepatocellular injury.

This corresponds to MASH in metabolic disease.

Stage 3: Fibrosis

Persistent inflammation and injury stimulate the formation of scar tissue.

Fibrosis is usually staged from F0 to F4.

Stage 4: Cirrhosis

Extensive fibrosis changes the structure of the liver and impairs its function.

Stage 5: Liver failure and complications

Advanced cirrhosis can lead to:

• ascites
• gastrointestinal bleeding
• hepatic encephalopathy
• jaundice
• kidney dysfunction
• severe infections
• liver failure

Liver cancer can also develop, particularly in advanced liver disease.

Fibrosis is commonly classified histologically as:

Fibrosis is particularly important because the amount of liver scarring is one of the strongest predictors of long-term liver-related outcomes.

Importantly, the quantity of liver fat seen on an ultrasound does not necessarily tell how much fibrosis a person has.

Fatty liver disease is frequently asymptomatic.

A person can have substantial disease without feeling ill.

When symptoms occur, they may include:

• fatigue
• general weakness
• vague discomfort in the upper-right abdomen
• reduced exercise tolerance

NIDDK describes MASLD/NAFLD as commonly silent, with fatigue or upper-right abdominal discomfort occurring in some people.

Symptoms generally become more apparent when significant liver damage or cirrhosis develops.

Possible manifestations include:

• jaundice
• abdominal swelling
• leg swelling
• easy bruising
• muscle wasting
• loss of appetite
• weight loss
• itching
• confusion
• gastrointestinal bleeding

These symptoms require medical assessment.

A common misconception is:

“Fatty liver is only fat, so it is harmless.”

This is incorrect.

Simple steatosis may remain relatively stable, but some individuals develop progressive inflammation and fibrosis.

The major long-term concern is not merely the presence of liver fat; it is progressive fibrosis and its complications.

MASH can ultimately lead to cirrhosis, liver failure and liver cancer.

MASLD is closely associated with cardiovascular disease.

Many individuals with MASLD have accompanying:

• obesity
• diabetes
• hypertension
• dyslipidemia
• insulin resistance

Consequently, cardiovascular disease is a major health concern in people with metabolic fatty liver disease.

For many patients, managing cardiovascular and metabolic risk factors is as important as treating the liver itself.

Diagnosis generally involves a combination of:

1. medical history
2. physical examination
3. blood tests
4. imaging
5. non-invasive fibrosis assessment
6. occasionally liver biopsy

NIDDK notes that clinicians use medical history, examination, blood tests, imaging and, in selected circumstances, liver biopsy to evaluate fatty liver disease.

A clinician may ask about:

• body weight
• weight changes
• diabetes
• blood pressure
• cholesterol
• diet
• physical activity
• alcohol consumption
• medications
• family history
• other liver diseases

The purpose is not simply to identify liver fat but to determine why it developed and whether progressive disease is present.

Physical examination may include assessment of:

• body weight
• body mass index
• waist circumference
• blood pressure
• signs of insulin resistance
• liver enlargement
• spleen enlargement
• ascites
• muscle loss
• jaundice

Advanced liver disease may produce physical signs of cirrhosis.

Commonly measured tests include:

• ALT
• AST
• alkaline phosphatase
• bilirubin
• albumin
• platelet count
• glucose
• HbA1c
• lipid profile

Liver enzymes can provide useful information, but normal ALT and AST do not exclude clinically important fatty liver disease or fibrosis.

NIDDK notes that clinicians may use routine blood tests and fibrosis scores such as FIB-4 or APRI to help assess the likelihood of advanced fibrosis.

FIB-4 is a non-invasive fibrosis risk score calculated from:

• age
• AST
• ALT
• platelet count

It is useful for initial risk stratification.

It does not directly measure fibrosis.

People with higher-risk results may require further assessment with elastography or specialist evaluation.

Abdominal ultrasound is commonly used to detect hepatic steatosis.

It is:

• widely available
• non-invasive
• relatively inexpensive
• radiation-free

However, conventional ultrasound has important limitations.

It can identify liver fat but generally cannot accurately determine the amount of inflammation or fibrosis.

NIDDK specifically notes that routine imaging can show liver fat but cannot reliably distinguish simple fatty liver from steatohepatitis or determine the degree of fibrosis.

CT scanning can demonstrate fatty changes in the liver and evaluate other abdominal structures.

However, CT is not generally the primary tool for staging metabolic liver disease.

Radiation exposure is another consideration.

MRI can provide more detailed assessment of liver fat.

Specialized MRI techniques such as MRI-PDFF can quantify hepatic fat with greater precision than conventional ultrasound.

MRI-based techniques are particularly useful in research and selected clinical situations.

Elastography evaluates liver stiffness.

Common methods include:

• vibration-controlled transient elastography
• shear-wave elastography
• magnetic resonance elastography

Increased liver stiffness can indicate fibrosis, although stiffness can also be affected by other factors.

AASLD identifies non-invasive blood- and imaging-based assessment as important components of modern fibrosis evaluation.

FibroScan, technically vibration-controlled transient elastography, is widely used to estimate liver stiffness and, with controlled attenuation parameter measurements, assess liver steatosis.

It is:

• quick
• non-invasive
• generally painless
• repeatable

It has become an important tool for identifying patients who may have significant fibrosis.

A liver biopsy involves removing a small sample of liver tissue for microscopic examination.

It can demonstrate:

• steatosis
• inflammation
• hepatocyte injury
• fibrosis
• cirrhosis
• other liver diseases

Historically, biopsy has been regarded as the reference method for diagnosing and staging steatohepatitis and fibrosis.

However, it is invasive and is not required for every person with fatty liver disease.

NIDDK notes that biopsy may be considered when advanced disease is suspected, when non-invasive tests are inconclusive or when another liver disease needs to be excluded.

When fatty liver is discovered, clinicians may need to exclude other causes of liver abnormalities, including:

• viral hepatitis
• autoimmune liver disease
• hemochromatosis
• Wilson disease
• alpha-1 antitrypsin deficiency
• alcohol-associated liver disease
• drug-induced liver injury
• other metabolic disorders

The appropriate investigation depends on the individual clinical situation.

Treatment depends on:

• the cause of steatosis
• the degree of liver fat
• presence of MASH
• fibrosis stage
• diabetes
• obesity
• cardiovascular risk
• alcohol consumption
• other medical conditions

For many people with MASLD, lifestyle and metabolic-risk management remain the foundation of treatment.

For people with overweight or obesity, gradual, sustained weight loss can substantially improve liver health.

Weight reduction can decrease:

• liver fat
• insulin resistance
• inflammation
• metabolic risk

Greater weight loss is generally associated with greater improvement in steatohepatitis and fibrosis.

AASLD educational material notes that approximately 5–10% weight reduction is associated with meaningful improvement in steatosis, inflammation and fibrosis.

Weight loss should generally be approached as a long-term health intervention rather than an extreme short-term diet.

There is no single universally prescribed “fatty liver diet.”

However, evidence supports dietary patterns emphasizing:

• vegetables
• fruits in appropriate portions
• whole grains
• legumes
• nuts
• seeds
• fish
• unsaturated fats

A Mediterranean-style dietary pattern is commonly recommended because it can improve overall metabolic health.

Reducing:

• sugar-sweetened beverages
• excessive added sugars
• highly processed foods
• excessive saturated fat
• excess calories

can also be beneficial.

NIDDK recommends healthy eating, appropriate portion sizes and weight management and suggests replacing saturated and trans fats with unsaturated fats.

Exercise is an important component of treatment.

Both:

• aerobic exercise, and
• resistance training

can improve metabolic health and reduce liver fat.

Examples include:

• brisk walking
• cycling
• swimming
• jogging
• strength training

Exercise can be beneficial even when weight loss is modest.

For people with fatty liver disease, alcohol consumption should be discussed with a healthcare professional.

Those with alcohol-associated liver disease generally need to stop alcohol completely.

For people with MASLD, the appropriate recommendation depends on the individual’s disease severity and risk profile. Alcohol can compound liver injury, particularly when significant fibrosis or other liver disease is present.

Management commonly includes appropriate treatment of:

• type 2 diabetes
• hypertension
• high cholesterol
• obesity
• sleep apnea
• cardiovascular disease

Treating these conditions can improve overall health and may also improve the metabolic drivers of fatty liver disease.

The pharmacological treatment of fatty liver disease has changed rapidly in recent years.

Importantly, not every person with fatty liver needs a liver-directed medication.

Medication decisions depend heavily on the presence of MASH, fibrosis stage and metabolic comorbidities.

Resmetirom, marketed in the United States as Rezdiffra, became the first drug specifically approved by the U.S. Food and Drug Administration for adults with noncirrhotic MASH/NASH with moderate-to-advanced fibrosis (F2–F3), to be used with diet and exercise. The FDA approved it in March 2024 under the accelerated-approval pathway.

Resmetirom is a thyroid hormone receptor-beta agonist designed to influence hepatic lipid metabolism.

Its approval does not mean that resmetirom is appropriate for everyone with fatty liver.

It is specifically intended for appropriately selected patients with significant fibrosis and without decompensated cirrhosis.

Another major development occurred in August 2025, when the FDA approved Wegovy (semaglutide) for adults with MASH and moderate-to-advanced fibrosis.

Semaglutide is a GLP-1 receptor agonist already widely used for obesity and other metabolic indications.

In the FDA-reviewed phase 3 data, 63% of participants receiving semaglutide achieved MASH resolution without worsening of fibrosis compared with 34% receiving placebo, while 37% achieved improvement in fibrosis without worsening of MASH compared with 22% receiving placebo at the interim 72-week analysis. The confirmatory trial remains ongoing.

This represents an important shift in the treatment landscape because therapies targeting metabolic disease can also produce clinically meaningful effects on liver disease.

For appropriately selected people with severe obesity, metabolic/bariatric surgery can produce substantial and sustained weight loss and may improve MASLD and MASH.

It is not a treatment for every patient and requires assessment of:

• obesity severity
• metabolic disease
• surgical risk
• nutritional status
• liver disease stage

Liver transplantation may be required when fatty liver disease progresses to irreversible, decompensated end-stage liver disease or certain liver cancers.

Transplantation replaces the severely diseased liver with a donor liver.

Because metabolic risk factors can persist after transplantation, long-term management remains necessary.

In many people, liver fat accumulation can substantially improve or even resolve, particularly when the underlying metabolic cause is addressed.

Improvement may occur through:

• weight reduction
• improved insulin sensitivity
• physical activity
• healthier dietary patterns
• treatment of diabetes
• treatment of dyslipidemia
• appropriate medication
• avoidance of harmful alcohol exposure

Even fibrosis may regress in some patients when the underlying cause is effectively controlled.

However, advanced cirrhosis may be irreversible or only partially reversible.

Yes.

The progression is not inevitable, but a subset of patients with MASH develop progressive fibrosis.

The general sequence is:

Steatosis → MASH → fibrosis → advanced fibrosis → cirrhosis

Once cirrhosis develops, complications can include:

• portal hypertension
• ascites
• variceal bleeding
• hepatic encephalopathy
• jaundice
• liver failure
• hepatocellular carcinoma

Advanced metabolic liver disease can increase the risk of hepatocellular carcinoma (HCC), the most common primary liver cancer.

The risk is particularly high in people with cirrhosis.

However, HCC can occasionally occur in people with metabolic fatty liver disease without established cirrhosis.

This is one reason why identifying high-risk patients and appropriately monitoring advanced disease is important.

The relationship between fatty liver and diabetes is bidirectional.

Insulin resistance promotes liver fat accumulation.

At the same time, hepatic metabolic dysfunction can contribute to worsening glucose regulation.

Thus:

Insulin resistance → liver fat → metabolic dysfunction → increased diabetes risk

and:

Type 2 diabetes → increased risk of MASLD/MASH and fibrosis

Abnormal lipid metabolism is closely associated with MASLD.

Patients may have:

• high triglycerides
• high LDL cholesterol
• low HDL cholesterol

Treatment of dyslipidemia is therefore an important component of overall cardiovascular-risk management.

Statins are commonly used when clinically indicated for cardiovascular risk reduction; the presence of MASLD alone is not generally a reason to withhold appropriate lipid-lowering therapy.

Obesity is one of the strongest population-level drivers of MASLD.

However, the relationship is not absolute.

There are individuals with obesity who do not develop significant liver disease and individuals without obesity who develop MASLD and MASH.

This phenomenon is sometimes described as lean MASLD.

Metabolic health, genetics, body-fat distribution and lifestyle all influence risk.

MASLD can also occur in children and adolescents.

Risk increases with:

• obesity
• insulin resistance
• type 2 diabetes
• metabolic syndrome
• family history

Because childhood metabolic liver disease can persist into adulthood, early recognition and family-based lifestyle interventions are important.

South Asian populations have attracted particular attention in fatty liver research because metabolic dysfunction can develop at comparatively lower body-mass indices than in some other populations.

This means that using body weight alone may underestimate metabolic risk.

A person with a relatively modest BMI may nevertheless have:

• abdominal adiposity
• insulin resistance
• diabetes
• dyslipidemia
• fatty liver

Consequently, metabolic assessment should not rely exclusively on BMI.

The prognosis of fatty liver disease varies greatly.

A person with simple steatosis and no fibrosis may have a substantially different prognosis from someone with F3 fibrosis or cirrhosis.

Important prognostic factors include:

• fibrosis stage
• diabetes
• obesity
• age
• cardiovascular disease
• alcohol exposure
• genetic susceptibility
• progression of metabolic disease

Among liver-related factors, fibrosis stage is particularly important.

Prevention focuses primarily on maintaining metabolic health.

Important measures include:

• maintaining a healthy body weight
• avoiding excessive calorie intake
• regular physical activity
• eating a balanced diet
• limiting sugary drinks
• managing diabetes
• controlling blood pressure
• treating abnormal cholesterol
• avoiding harmful alcohol consumption
• avoiding unnecessary medications or supplements that may injure the liver

Because MASLD is strongly associated with metabolic disease, prevention of obesity and type 2 diabetes can also reduce population-level disease burden.

“Fatty liver means I drink too much alcohol.”

False.

Metabolic fatty liver disease can occur in people who drink little or no alcohol.

“If my liver enzymes are normal, my liver is healthy.”

False.

Normal ALT and AST do not completely exclude fatty liver, MASH or significant fibrosis.

“Fatty liver always causes symptoms.”

False.

Many people have no symptoms for years.

“Fatty liver automatically means cirrhosis.”

False.

Fatty liver ranges from simple steatosis to advanced liver disease.

“Only overweight people develop fatty liver.”

False.

Lean individuals can develop MASLD.

“A detox can clean the liver.”

There is no scientifically established “liver detox” that reverses metabolic fatty liver disease.

The liver already performs its own detoxification functions. Treating the underlying metabolic causes is much more important than commercial detox products.

“One particular food causes fatty liver.”

Usually not.

Overall energy balance, metabolic health, diet quality, physical activity, genetics and other factors are more important than a single food.

Fatty liver disease is currently one of the most active areas of hepatology research.

Research is investigating:

• new antifibrotic drugs
• metabolic therapies
• GLP-1 and related pathways
• thyroid hormone receptor pathways
• combination therapies
• personalized medicine
• genetic risk
• microbiome-based approaches
• non-invasive biomarkers
• artificial-intelligence-assisted imaging
• new methods of fibrosis assessment

The rapid development of new treatments is reflected by recent AASLD updates addressing both resmetirom and semaglutide therapy for MASH.

The terminology can be confusing because the field has recently undergone a major nomenclature change.

The newer terminology emphasizes metabolic dysfunction rather than defining the condition primarily through the absence of alcohol.

Older terminology remains common in research papers, medical records and drug-regulatory documents.

Fatty liver disease is not a single condition but a broad spectrum of disorders characterized by excessive fat accumulation in the liver.

For many people, particularly those with metabolic dysfunction, it begins quietly and may cause no symptoms. In some individuals, however, persistent metabolic stress leads to inflammation, hepatocyte injury and progressive fibrosis.

The most important distinction is therefore not simply:

“Does this person have fat in the liver?”

but rather:

“Why is the fat there, and has it caused inflammation or fibrosis?”

Modern medicine has moved beyond viewing fatty liver as a minor incidental finding. MASLD is now recognized as a major metabolic and liver disease, while MASH with significant fibrosis is an important progressive condition requiring risk assessment and, in selected patients, pharmacological treatment.

Lifestyle intervention remains fundamental. At the same time, the therapeutic landscape is changing rapidly: resmetirom became the first FDA-approved drug specifically targeting noncirrhotic MASH with moderate-to-advanced fibrosis in 2024, followed by semaglutide for the same broad disease stage in 2025.

The central lesson is that fatty liver is often detectable before irreversible liver failure occurs. Identifying metabolic risk factors, assessing fibrosis rather than relying solely on liver enzymes or ultrasound, and addressing the underlying causes can substantially alter the long-term trajectory of the disease.

Fat in the liver is a finding. Fibrosis is the warning sign. Progressive fibrosis is what turns fatty liver from a metabolic problem into potentially serious chronic liver disease.

This article is intended as an encyclopedia-style educational overview, not as a diagnosis or individualized treatment plan. Current treatment decisions—particularly regarding prescription medicines such as resmetirom or semaglutide—should be made with an appropriately qualified clinician based on fibrosis stage, comorbidities, contraindications and local regulatory approvals.