Fatty liver disease (MASLD), explained

What it is, and the new name

Fatty liver disease is a build-up of fat in the liver (NIDDK). For years it was called nonalcoholic fatty liver disease (NAFLD), with a more serious form called nonalcoholic steatohepatitis (NASH). The newer names are metabolic dysfunction-associated steatotic liver disease (MASLD) and metabolic dysfunction-associated steatohepatitis (MASH) (NIDDK). The new names point to the main driver: metabolic problems such as excess weight and type 2 diabetes, rather than alcohol.

There are two broad forms (NIDDK) (NIDDK):

• Fat only (steatosis). Most people with this form do not go on to liver damage, though they have higher risks elsewhere in the body.
• Fat with inflammation and liver cell damage (MASH). This form can lead to scarring (fibrosis), cirrhosis and liver cancer.

How common it is

NIDDK estimates that about 24% of US adults have fatty liver disease, and about 1.5% to 6.5% have the inflammatory form (NIDDK). Among racial and ethnic groups in the US, it is most common in Hispanic people (NIDDK).

Who is more likely to have it

Obesity, metabolic syndrome and type 2 diabetes are the main risk factors (NIDDK). NIDDK reports that it is found in up to 75% of people with overweight and more than 90% of people with severe obesity, and in one-third to two-thirds of people with type 2 diabetes (NIDDK).

If you are not sure where you stand, our BMI calculator, waist-to-height ratio and diabetes risk test cover the main risk factors.

Symptoms

NIDDK calls it a silent disease, with few or no symptoms (NIDDK). It is often found by chance, on a blood test or scan done for another reason. Waiting for symptoms is not a good plan, because scarring can build up quietly.

Why it matters beyond the liver

People with fatty liver disease have higher risks of heart and blood vessel disease, which is the leading cause of death in this group, and of type 2 diabetes, metabolic syndrome, high blood pressure and abnormal cholesterol and triglycerides (NIDDK). That is why a fatty liver finding is a good moment to check your heart risk too.

How doctors check for scarring

The key question is not how much fat there is, but whether there is advanced scarring (fibrosis). The American Association for the Study of Liver Diseases sets out a stepwise approach (AASLD 2023):

FIB-4 uses your age, AST, ALT and platelet count (Sterling 2006), numbers that are often already on a recent blood test. In adults with fatty liver disease, the 1.30 and 2.67 cutoffs separate low, in-between and higher risk of advanced scarring (Shah 2009). You can work it out with our FIB-4 calculator, and read more in FIB-4 explained. What the AST to ALT comparison can and cannot tell you is on the AST/ALT ratio calculator.

What helps

Weight loss is the best-studied step. NIDDK says losing at least 3% to 5% of body weight can reduce liver fat, and losing up to 7% to 10% may be needed to reduce liver inflammation and scarring (NIDDK). For a 200-pound person, 7% to 10% is 14 to 20 pounds.

Treatment options for the inflammatory form with scarring have been changing, so ask a clinician what applies to you. This page does not give treatment advice.

Common questions

Is MASLD the same as NAFLD?

They describe the same condition under a newer name, which focuses on metabolic risk factors (NIDDK). You may see either on a report.

Can a normal liver blood test rule it out?

No. Fatty liver disease often has few or no signs (NIDDK), and liver enzymes can be normal. FIB-4 and imaging tell you more about scarring than a single enzyme value.

Does fatty liver always get worse?

No. Most people with fat alone do not develop liver damage (NIDDK). The inflammatory form is the one that can progress to cirrhosis (NIDDK).