Fatty Liver: What Is It, and Is It Dangerous?

Fatty liver is the build-up of more fat than normal inside the liver cells. Fatty liver arising from metabolic causes is now called MASLD (Metabolic Dysfunction-Associated Steatotic Liver Disease). It used often to be called NAFLD — non-alcoholic fatty liver disease.

Fatty liver is common. Most people with it never develop serious liver disease; but in some, inflammation and then scar tissue (fibrosis) are added to the fat.

So the question that matters is not only “Is my liver fatty?” but “Is there fibrosis in my liver?”

Why does the liver become fatty?

Fatty liver is closely bound up with metabolic problems:

• Excess weight, and particularly fat around the waist
• Insulin resistance
• Type 2 diabetes
• Raised triglycerides and cholesterol
• High blood pressure
• A sedentary life

Alcohol, some medicines, and less commonly certain metabolic, hormonal or genetic conditions can also cause fat to gather in the liver.

For that reason, seeing “hepatic steatosis” on an ultrasound does not automatically mean every patient has the same disease.

What do MASLD and MASH mean?

The two terms are different.

• MASLD — fat in the liver together with at least one cardiometabolic risk factor.
• MASH — the more advanced form, where liver cell injury and inflammation accompany the fat. Its former name was NASH.

Broadly, the disease can move along this path:

Fat → MASH → Fibrosis → Cirrhosis

But this does not mean every patient with a fatty liver will develop cirrhosis.

Does it cause symptoms?

Most of the time it causes none. Fatty liver is often found incidentally, on an ultrasound or in blood tests.

Some people have;

• Tiredness
• Fatigue
• Fullness or discomfort in the right upper abdomen

but none of these is specific to fatty liver.

If ALT and AST are normal, is the liver healthy?

Not always.

Someone with a fatty liver can have normal ALT and AST. Normal liver enzymes do not completely rule out advanced fibrosis.

Equally, a raised ALT or AST does not by itself show how far the disease has progressed. Looking at the liver enzymes alone is therefore not enough.

What do Grade 1, Grade 2 and Grade 3 mean on ultrasound?

The appearance of the fat on ultrasound is sometimes graded:

• Grade 1 Mild fatty change
• Grade 2 Moderate fatty change
• Grade 3 Marked fatty change

But there is an important point: the grade of the fat and the degree of fibrosis are not the same thing.

Ultrasound can show the fat, but it cannot always reliably say how much fibrosis is in the liver.

What is fibrosis, and why does it matter?

Fibrosis is scar tissue forming in the liver over time.

In fatty liver disease, one of the most important long-term questions is whether advanced fibrosis or cirrhosis is present. Current practice therefore puts weight on non-invasive assessment of fibrosis in suitable patients.

• FIB-4, calculated from age, AST, ALT and platelet count, can be used as a first step.
• If the risk is high or unclear, FibroScan (transient elastography) or other non-invasive fibrosis tests can take the assessment further.

Not everyone with a fatty liver needs a biopsy.

Does fatty liver turn into cirrhosis?

In some patients it can, but in most it does not.

The risk is higher particularly in those;

• With MASH
• With advanced fibrosis
• With type 2 diabetes
• With obesity
• Carrying more than one metabolic risk factor

So the focus should be on the risk of fibrosis, not on the amount of fat alone.

Does fatty liver cause cancer?

Simple fatty change is not cancer.

But when the disease progresses to advanced fibrosis and especially cirrhosis, the risk of hepatocellular carcinoma (liver cancer) can rise. The clinical spectrum of MASLD runs from fat through MASH and fibrosis to cirrhosis.

This does not mean that someone whose ultrasound shows a fatty liver will get cancer.

Can fatty liver improve?

Yes. Especially early on, it can regress considerably.

In people carrying excess weight, weight loss is one of the most important parts of treatment. Losing roughly 5–10% of body weight can bring meaningful benefit for the liver and for metabolic health; greater and sustained weight loss can bring greater benefit for MASH and fibrosis.

A Mediterranean-style diet, regular physical activity, reducing excess weight, good control of diabetes and treatment of blood lipids are the mainstays.

Is there drug treatment?

Treatment is no longer only “diet and exercise”. Treating the patient’s obesity, diabetes, cholesterol and cardiovascular risk appropriately is an important part of managing MASLD.

In recent years, disease-directed drug treatments for MASH with fibrosis have also begun to come into use. In the United States, for example, resmetirom and more recently semaglutide have come up for MASH in particular groups of patients.

These are not drugs given to everyone with a fatty liver; patients are selected according to the degree of fibrosis and the conditions they have alongside it.

What should be assessed in a patient with fatty liver?

Looking only at the word “steatosis” in the ultrasound report is not enough. The patient’s;

• Weight and waist measurement
• Blood glucose / HbA1c
• Lipid profile
• ALT, AST, GGT
• Platelet count
• Alcohol use and the medicines they take

should all be assessed together. Where necessary, the risk of fibrosis is investigated with FIB-4 and elastography.

When should more care be taken?

If a fatty liver is accompanied by;

• A low platelet count
• An enlarged spleen
• Fluid in the abdomen
• Jaundice
• Swelling of the legs
• Vomiting blood
• A change in consciousness

then a detailed assessment for advanced liver disease is needed.

Remember

• Fatty liver Is a common condition.
• The commonest association Excess weight, diabetes and metabolic disturbance.
• Early on It can regress with lifestyle change and weight control.
• Grade 1–2–3 fatty change Is not a stage of fibrosis.
• One of the key questions “Is there fibrosis?”
• Normal ALT and AST Do not by themselves rule out advanced fibrosis.
• Fatty liver Is not cancer.
• Not every fatty liver Turns into cirrhosis.