Metabolic dysfunction-associated steatotic liver disease (MASLD), nonalcoholic fatty liver disease (NAFLD), and fatty liver disease all describe conditions where too much fat builds up in the liver, often tied to metabolic health.
Doctors now use several terms to describe fatty liver conditions, which can get confusing. You may hear MASLD, NAFLD, or simply fatty liver disease.
MASLD is the updated term for NAFLD. It refers to fat building up in the liver from metabolic causes rather than alcohol use.
“Fatty liver disease” is an umbrella term that includes MASLD and alcohol-associated liver disease (ALD). In ALD, fat in the liver develops from alcohol use.
The switch from NAFLD to MASLD was made to highlight the role of metabolic health and reduce stigmatizing language around alcohol. Still, many people and healthcare professionals continue to use NAFLD.
What about MAFLD?
In 2020, experts proposed metabolic-associated fatty liver disease (MAFLD) as a replacement for NAFLD. Although it was never fully adopted, it helped set the stage for the official shift to MASLD.
MASLD develops when metabolic dysfunction causes too much fat to build up in your liver.
Your metabolism is how your body produces, converts, uses, and stores energy. It involves multiple organs and hormones, including the liver, pancreas, fat tissue, muscles, and digestive system.
When one of these areas doesn’t work properly, insulin resistance
Fat buildup in the liver is called “steatosis.” When steatosis from metabolic dysfunction reaches disease levels, doctors may diagnose MASLD.
To confirm MASLD, doctors check for fat in the liver through a biopsy or imaging. Along with no significant alcohol use, at least one of the following criteria must also be present:
- overweight or obesity
- high blood sugar or insulin resistance
- high blood pressure
- high triglycerides
- low HDL (“good”) cholesterol
If left untreated, MASLD can progress to metabolic dysfunction-associated steatohepatitis (MASH), where fat in your liver causes inflammation, damage, or scarring (cirrhosis).
NAFLD was the original term doctors used before MASLD. It described fat buildup in the liver that wasn’t caused by heavy alcohol use.
NAFLD and MASLD aren’t the same, though. NAFLD had broader diagnostic criteria. For a diagnosis, the following three criteria must be met:
- Evidence of steatosis (fat in the liver): seen on imaging or biopsy
- No significant alcohol use: defined as more than 30 grams (g)/day in men or 20 g/day in women
- No other known causes of liver fat: such as viral hepatitis, genetic conditions, or certain medications
Fatty liver disease is an umbrella term for several conditions where fat buildup in the liver causes health problems.
One type of MASLD. Other types include:
- ALD: liver fat caused by heavy alcohol use
- Metabolic dysfunction and alcohol associated/related liver disease (MetALD): a
combination of metabolic dysfunction and significant alcohol use - Secondary fatty liver: fat buildup linked to other causes, such as certain medications or genetic conditions
The primary difference between MASLD and NAFLD is how doctors diagnose them.
- MASLD requires at least one metabolic risk factor, such as obesity, high blood pressure, or abnormal blood sugar.
- NAFLD didn’t require metabolic risk factors. Instead, doctors made the diagnosis by ruling out other causes of liver fat, which sometimes led to vague or incomplete results.
| NAFLD | MASLD |
|---|---|
| evidence of steatosis on imaging or biopsy | evidence of steatosis on imaging or biopsy |
| no significant alcohol use (more than 30 g/day in men or 20 g/day in women) | no significant alcohol use (more than 30 g/day in men or 20 g/day in women) |
| no other causes of liver fat (such as viral hepatitis, genetic conditions, or certain medications) | at least one metabolic risk factor, such as: • overweight or obesity • abnormal blood glucose • high blood pressure • high triglycerides • low (“good”) HDL cholesterol |
Some research suggests that mortality rates are slightly higher in MASLD compared to the broader diagnosis of NAFLD. Experts believe this reflects the stricter, more specific criteria tied to metabolic health.
The shift from NAFLD to MASLD is both clinically and personally important.
The new name highlights the root cause: metabolic dysfunction. This helps doctors identify people at risk earlier and guide treatment more effectively. It also removes potentially stigmatizing terms like “nonalcoholic” and “fatty.”
By focusing on what causes MASLD rather than what doesn’t, doctors can target health factors that can be changed. The change also makes room for more precise diagnoses, such as MetALD, which involves both metabolic dysfunction and alcohol-related causes.
MASLD, NAFLD, and fatty liver disease all describe fat buildup in the liver, but the terms aren’t interchangeable. MASLD is the current diagnostic term that replaced NAFLD, while fatty liver disease is the broader umbrella term.
The switch to MASLD highlights the root cause: metabolic dysfunction. This makes the diagnosis more specific and helps reduce stigmatizing language.