Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD)

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a liver condition in which too much fat builds up in the liver, but not due to alcohol use.

Overview

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a condition in which excess fat builds up in the liver. This buildup of fat is not caused by heavy alcohol use. When heavy alcohol use causes fat to build up in the liver, that condition is called alcohol-associated liver disease (ALD). People typically develop one type or the other, although sometimes a person with one form is later diagnosed with the other.

There are two types of MASLD:

  • Metabolic dysfunction-associated steatotic liver (MASL) is a condition where there is fat in the liver with little or no inflammation or liver damage.
  • Metabolic dysfunction-associated steatohepatitis (MASH) is a condition where there is fat in the liver plus inflammation and liver damage. MASH used to be called nonalcoholic steatohepatitis (NASH).

MASL is the milder form of MASLD. It typically does not progress to cause liver damage or complications, though it can cause pain from an enlarged liver. MASH is more serious. The inflammation and liver damage of MASH can cause a form of liver scarring called fibrosis. MASH may also lead to cirrhosis, in which the liver is permanently scarred and damaged. Cirrhosis, in turn, can lead to liver cancer.

Related Terms: MASLD used to be called non-alcoholic fatty liver disease (NAFLD). 

Signs and Symptoms

MASLD is often called a “silent disease” because most people have few or no symptoms. You may not have symptoms even if you develop cirrhosis due to MASH.

When symptoms do occur, they may include:

  • Feeling tired or fatigued, or becoming tired easily
  • Discomfort over the liver, in the upper right side of the abdomen

Important: In children, once symptoms appear, permanent liver damage may have already occurred.

Liver Complications

People with MASL typically do not develop liver complications, though they have a higher risk for other health problems. However, people with MASH can develop serious liver complications, including:

People with MASH also have an increased chance of dying from liver-related causes.

Compared with people who develop MASLD during adulthood, people who develop MASLD during childhood are more likely to have MASH and related complications as adults. Children with MASH may develop cirrhosis during childhood, though complications such as liver failure and liver cancer usually arise in adulthood.

Metabolic Syndrome

People with MASLD are at higher risk for a group of conditions linked to overweight and obesity collectively known as metabolic syndrome. These conditions include high levels of fat molecules called triglycerides in the blood, low HDL (or “good”) cholesterol, high blood pressure, and high blood sugar that can progress to type 2 diabetes. People with MASLD or metabolic syndrome also have a greater chance of heart disease, stroke, and hardening of the arteries.

Causes and Risk Factors

Experts are still studying the causes of MASLD. Research suggests that certain health conditions, genes, and dietary factors may make a person more likely to develop MASLD.

Health Conditions

You are more likely to develop MASLD if you have:

Having more of these health conditions increases the chance of developing MASH.

Demographics

While MASLD occurs in people of all races and ethnicities, it is most common among Hispanic individuals, followed by non-Hispanic White individuals and Asian Americans. MASLD is less common among non-Hispanic Black individuals. On average, Asian Americans with MASLD have a lower body mass index (BMI) than non-Hispanic White individuals with MASLD.

In children, MASLD is more common in older children than younger children, and more common in boys than in girls. MASLD is most common in Hispanic children and Asian American children, followed by White children, and is less common in Black children.

Genes

Researchers have found that certain genes may make a person more likely to develop MASLD. These genes may help explain why MASLD is more common in certain racial and ethnic groups. Experts are still studying the genes that may play a role in MASLD.

Birth Weight

Research suggests that children who had a high or low birth weight are more likely to develop MASLD.

Diet and the Digestive System

Researchers are studying whether diets high in fructose, a sugar found in table sugar and commonly added to drinks and foods, may increase the risk of MASLD. Scientists have also found differences between the bacteria living in the digestive systems of people who have MASLD and those who do not. Experts are still studying how this group of microbes, called the microbiome, may affect MASLD.

Other Causes of Fatty Liver

When fatty liver is not caused by MASLD or heavy alcohol use, it may be due to:

  • Disorders called lipodystrophies, which cause the body to use or store fat improperly
  • Rapid weight loss or malnutrition
  • Some medicines, including corticosteroids, HIV treatment, estrogens, and certain cancer medicines
  • Exposure to some toxins
  • Rare genetic diseases, such as Wilson disease and hypobetalipoproteinemia

Prevention Guidance

You may be able to prevent MASLD by:

  • Being physically active regularly
  • Eating a healthy diet
  • Limiting your portion sizes
  • Maintaining a healthy weight

Diagnosis

Doctors use medical history, a physical exam, and tests to diagnose MASLD.

Your doctor will ask about the following regarding your medical history:

  • Health conditions that raise your risk for MASLD, such as overweight or obesity, insulin resistance, type 2 diabetes, high triglycerides, abnormal cholesterol, or metabolic syndrome
  • Diet and lifestyle factors, such as lack of physical activity, eating a diet high in sugar, or drinking sugary beverages
  • Alcohol intake to rule out alcohol-associated liver disease

To diagnose MASLD in children, the doctor will also ask about family members with the condition.

During a physical exam, a doctor will:

  • Check your weight and height to calculate your body mass index (BMI), which can help determine if you have overweight or obesity
  • Look for signs of MASL or MASH, such as an enlarged liver
  • Look for signs of insulin resistance, such as darkened skin patches over the knuckles, elbows, and knees
  • Look for signs of cirrhosis, such as an enlarged spleen, fluid buildup in the abdomen, and muscle loss

A healthcare professional may take a blood sample and send it to a lab. Your doctor may suspect MASLD if blood tests show increased levels of the liver enzymes alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Your doctor may also use blood test results to calculate special scores that help identify or rule out advanced liver fibrosis, such as the FIB-4 or APRI.

Routine imaging tests can show fat in the liver, but they cannot show inflammation or fibrosis. Your doctor may use the following imaging tests:

  • Ultrasound: Uses safe, painless sound waves to create an image of the liver
  • Computed tomography (CT) scan: Uses X-rays and computer technology to create images of the liver
  • Magnetic resonance imaging (MRI): Uses radio waves and magnets to produce detailed images without X-rays
  • Elastography: A newer type of imaging test that can help determine if you have advanced liver fibrosis by measuring the stiffness of the liver

Liver biopsy is the only test that can prove a diagnosis of MASH and show clearly how severe the disease is. During a liver biopsy, a doctor takes small pieces of tissue from the liver. A pathologist then examines the tissue under a microscope to look for signs of damage or disease. Doctors only recommend liver biopsy for those more likely to have MASH with advanced fibrosis or when other tests suggest advanced liver disease.

Treatment and Management

Weight Loss

Doctors recommend weight loss to treat MASLD. If you are overweight or have obesity, losing weight by making healthy food choices, limiting portion sizes, and being physically active can reduce fat in the liver and decrease inflammation and fibrosis due to MASH. Losing weight may cause MASH to revert to the milder MASL form. Regaining weight may lead to the reappearance of MASH.

Losing at least 3% to 5% of your body weight can reduce fat in the liver. You may need to lose up to 7% to 10% of your body weight to reduce liver inflammation and fibrosis. Physical activity alone, even without weight loss, is also beneficial.

Doctors recommend losing weight gradually. Rapid weight loss and malnutrition can make liver disease worse.

For young children with overweight or obesity, doctors may suggest trying to maintain weight as height increases rather than aiming to lose weight. The most important goal is to avoid further excess weight gain.

Diet Changes

Changing the types of food you eat can help you lose weight and reduce fat in the liver. It is also important to minimize alcohol use, which can further damage the liver.

If a child has MASLD, the parent or caretaker should talk with a doctor about the child’s diet. The doctor may refer the child to a dietitian to help plan a well-balanced diet.

Medicines

There aren't any medicines approved to treat MASLD. However, some medicines have been approved to treat MASH in adults. If you have MASH, talk with your doctor about whether one of these treatments may be right for you. Researchers continue to look for new medicines to treat MASLD and MASH.

Before taking any dietary supplements, such as vitamins, or using any complementary or alternative medicines or practices, talk with your doctor. Some herbal products and supplements can damage the liver.

Treating MASH Complications

If MASH leads to cirrhosis, doctors can treat many complications with medicines, minor medical procedures, and surgery. People with liver failure or liver cancer may need a liver transplant to restore health.

Find Clinical Trials

Clinical trials uncover better ways to prevent, diagnose, treat, and understand diseases and conditions. To ensure results apply to everyone, volunteers of all ages, sexes, and backgrounds, including both healthy individuals and those with specific medical conditions, are needed. Find clinical trials on MASLD.

Research Information

The National Institutes of Health (NIH) is the largest public funder of biomedical research in the world. NIH invests most of its budget in medical research seeking to enhance life and to reduce illness and disability. NIH-funded research has led to breakthroughs and new treatments helping people live longer, healthier lives, and building the research foundation that drives discovery.

NIH conducts and supports clinical trials in liver diseases, including MASLD and MASH. These trials look for new ways to prevent, detect, or treat disease and improve quality of life. In particular, NIH’s NASH Clinical Research Network (NASH CRN) has conducted studies to advance understanding of the causes, development, complications, and treatment of NASH in children and adults.

Researchers are currently studying:

  • New treatments for MASH
  • How genes may increase the risk for MASLD
  • How liver diseases like MASLD develop and progress over time
  • How MASLD begins and progresses in children
  • New methods to measure the severity of MASLD without a liver biopsy

Find NIH-funded research projects using NIH RePORTER, a searchable database of current and past research projects supported by NIH and other federal agencies.