TGen.

Johanna DiStefano is head of TGen's Diabetes and Fibrotic Disease Unit.

Severe fatty liver disease is typically associated with obesity.

But a research review published in the journal Diabetology & Metabolic Syndrome shows lean people might be as vulnerable — if not more — to the illness and its consequences. 

"Our findings were a little unexpected. We thought that patients who were normal weight would maybe have a milder form of the disease than those with classical obesity associated with fatty liver disease. But that's not really what we saw," said lead author Johanna DiStefano, who leads TGen's Diabetes and Fibrotic Disease Unit.

The risk of non-alcoholic fatty liver disease rises with BMI. But many with obesity never develop it, while surprisingly many lean people do, and may suffer more severe illness and death.

"It's not what you would expect. This is the problem, because most people go into the doctor, if they're normal weight and they're otherwise healthy, the doctor's not even going to be thinking about fatty liver disease, right?" said DiStefano.

She added that more research is needed, but screenings should look beyond BMI to risk factors like diet, genetics, ethnicity and menopause status.

Nonalcoholic fatty liver disease describes a range of disorders, from simple fat accumulation in the liver to cirrhosis. In between lie many routes and stages of progression, including fibrosis, the accumulation of scar tissue from a malfunctioning immune response. 

DiStefano said specifics about the disease's prevalence in various populations are hard to nail down because studies sometimes use different criteria for what they consider "lean" and rely on noncomparable ways of detecting fatty liver disease.

"This is significant. We clearly need more studies in that we need to know more about this disease and how it develops in lean individuals," she said.

DiStefano's team is currently studying genetic variants in lean people who have fatty liver disease.