This is an ambiguous term. For example, on ultrasound, the report may mention presence of “fatty liver.” But any disease of the liver can cause this, as well as other diseases that don’t really affect the organ. So when we speak of “Fatty Liver” as a final diagnosis, we mean that there isn’t any other condition at all (see Liver Diseases). The two types of Fatty Liver are both called “non-alcoholic,” because alcohol by itself can result in infiltration of fat.
The two types of “Fatty Liver” are:
- Non-Alcoholic Fatty Liver Disease (NAFLD) [pronounced “NA-Feld”]
- Non-Alcoholic Steatohepatitis (NASH)
We’ll use the abbreviations from now on, because that’s how clinicians refer to them, the conditions are very similar, & yet quite different. By the way, the “Steato-” in NASH simply means “fat’ in ancient Greek.
The difference between NAFLD and NASH is that the latter involves inflammation (hence the suffix “-itis” in “hepatitis”). On liver biopsy, white blood cells are seen in NASH, but not in NAFLD. In life, NAFLD never causes any problem, whereas NASH destroys the liver. Most people who are told they have “fatty liver” (not due to alcohol or any other illness) just have NAFLD and will do well. But NASH will eventually lead to Cirrhosis, which is usually fatal without liver transplant.
We suspect one of these two conditions when we find elevated liver enzymes in blood tests (liver function tests — LFTs; the main enzymes are the ALT and AST). Then we order lots of labs for various chronic Liver Diseases, & usually don’t find anything (see Hepatitis Blood Tests, the final section dealing with Chronic Hepatitis). So we’re left with either NAFLD or NASH.
These can be distinguished by biopsy, which carries rare but serious risks. Hepatologists (liver specialists) used to do this for everyone, but since more and more patients wind up with “fatty liver”, a few will have complications from the procedure. So now the tendency is to do non-invasive (completely safe) tests called “elastography” to look for the beginning of early liver damage (“fibrosis”). If so, the patient has NASH. If not, it’s NAFLD. Sometimes we can even estimate this by calculating from a combination of common blood tests.
But then the problem is, what if those with NAFLD eventually get NASH (some will, most won’t)? Wouldn’t it be better to find out sooner, before any damage begins? Of course it would, but as of now, the only way is by biopsy.
Treatment is very difficult, because the only thing that works is weight loss. And that only works if patients are overweight or obese; most are, but not all. For NASH, high dose Vitamin E seems to help, but not for NAFLD (some studies suggest it might increase overall death rates in the long run, maybe from heart attacks, so we don’t recommend it “just in case”). A certain diabetes medication may hold promise (semaglutide), and other drugs may appear as well.
Years ago, we’d never heard of these conditions. They’re now becoming more & more common, due to our obesity epidemic. Experts think that in the future, we may see lots of people getting cirrhosis with liver failure while still relatively young. Moral — try hard to watch your weight, & if already overweight or obese, try hard to lose it.