By A.J. Hostetler 

A healthy weight does not always mean a healthy liver. 

That’s the main finding of a large international study that was recently published in the Journal of the American Medical Association. It showed that among people with metabolic dysfunction–associated steatotic liver disease, or MASLD, those with a healthy body weight may face the same risk of death and major health problems as those who are overweight or obese. 

MASLD affects about one-third of the world’s population. Anywhere between 10-20% of those adults would be classified as having a healthy body mass index (BMI) or being lean.  

Just as you can’t judge a book by its cover, you can’t judge liver health by body weight alone, said one of the study’s authors Juan Pablo Arab, M.D., director of alcohol sciences for the Stravitz-Sanyal Institute for Liver Disease and Metabolic Health at VCU and a hepatologist at VCU Health. 

“People with a normal BMI can still have significant liver disease. A person’s weight should not be the only measure of liver health,” Arab said. “Doctors should base testing and treatment on fibrosis, or liver scarring, rather than body weight alone.” 

Arab spoke with VCU Health News about what you need to know about lean MASLD and how the study’s findings can impact patient care. 

What is MASLD, and how is it different from lean MASLD? 

MASLD causes fat to build up in the liver, affecting about one in three adults worldwide. It is more common in people with obesity or type 2 diabetes. Some people develop MASLD even when their body mass index (BMI) is in the normal range. Doctors call this “lean MASLD.” 

Lean MASLD may affect 5% to 20% of people with MASLD, depending on the population and how the disease is measured. It appears to be especially common in Asian populations, but it affects people worldwide. 

Researchers are still learning why lean people develop MASLD. Possible factors include fat stored deep in the belly, low muscle mass, insulin resistance, genetic risk, changes in the gut, diet and other environmental factors. 

People with lean MASLD may also have problems with blood sugar, cholesterol or other parts of their metabolism. This means BMI alone may not show a person’s full health risk. 

How is MASLD diagnosed?  

Liver specialists can use a number of tests to evaluate your liver health, but two specific tests are commonly used to find liver scarring. One is the FIB-4 blood test, which was developed in part by hepatologist Richard Sterling, M.D., of VCU Health and clinical director of the liver institute. The other test measures liver stiffness using sound waves. It is often called a FibroScan. 

What do those tests tell us about lean MASLD? 

In the new study, we found that FibroScan was better at finding advanced scarring in lean patients than the FIB-4 test. Doctors may use these tests to decide whether a patient needs more testing or follow-up care. 

What else did the study find about lean MASLD? 

Body weight was not the best way to predict a patient’s future health. The amount of scarring, or fibrosis, in the liver was the most important factor. Severe scarring can lead to cirrhosis, liver cancer and liver failure. 

Our research looked at the health records of 18,326 people from more than 40 countries. All of them had liver biopsies, which allowed us to examine their liver tissue and measure damage. 

We looked at four main factors: 

• How common lean MASLD is 
• How it differs by region and ethnic group 
• How well commonly used tests detect liver scarring 
• Whether lean patients have a different risk of death or major liver problems 

About 6.7% of the patients were considered lean based on their BMI, and about 6% were considered lean based on their waist size. 

• Compared with patients who were overweight or obese, lean patients had: 
• Fewer health problems linked to metabolism. 
• Less liver inflammation and damage at the start of the study. 
• Similar long-term risks of death and major health problems. 

What’s the main take-away for doctors and patients 

These findings may help doctors identify patients who might otherwise be missed. When checking for MASLD risk, doctors should consider more than weight. Blood sugar, cholesterol, blood pressure, waist size, liver tests and family history may also provide important clues. 

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