Non-alcoholic fatty liver disease (NAFLD) is the term for a wide range of conditions caused by a build-up of fat within the liver cells. It is usually seen in people who are overweight or obese.
A healthy liver should contain little or no fat. Most people with NAFLD only carry small amounts of fat in their liver, which doesn't usually cause any symptoms. This early form of the disease is known as simple fatty liver, or steatosis.
Simple fatty liver is very common in the UK, reflecting the number of people who are obese or overweight. It is one of the most common forms of liver disease, with an estimated 25-30% people in the UK having early forms of NAFLD.
In most people, simple fatty liver is unlikely to cause harm, but that doesn't mean it's not a serious condition. This is because:
in some people, if the fat builds up and gets worse, it can eventually lead to inflammation (non-alcoholic steatohepatitis, or NASH) and scarring of the liver
as the disease is linked to being overweight or obese, people with any stage of the disease are more at risk of developing a strokeor heart attack – this risk appears to be higher in those who have NASH
NAFLD is often diagnosed after liver function tests (a type of blood test) produce an abnormal result and other liver conditions, such ashepatitis, are ruled out. However, NAFLD can be present even when routine liver blood tests are normal.
This page explains:
the four stages of NAFLD and the symptoms at each stage
who is affected, and the causes of NAFLD
living with NAFLD
Four stages of NAFLD
NAFLD is very similar to alcoholic liver disease, but is caused by factors other than drinking too much alcohol. The four stages are described below.
Stage 1: simple fatty liver (steatosis)
Hepatic steatosis is stage 1 of the condition. This is where excess fat builds up in the liver cells, but is considered harmless. There are usually no symptoms, and you may not even realise you have it until you receive an abnormal blood test result.
Stage 2: non-alcoholic steatohepatitis (NASH)
Only a few people with simple fatty liver go on to develop stage 2 of the condition, called non-alcoholic steatohepatitis (NASH). It is estimated that around 2-5% of the UK population has NASH.
NASH is a more aggressive form of the condition, when the liver has become inflamed. Inflammation is part of the body's response to injury, which suggests that cells in the liver are being damaged and that some liver cells are dying.
A person with NASH may have a dull or aching pain in the top right of their abdomen (over the lower right side of their ribs), although there may be no symptoms at all.
Unfortunately, routine blood tests alone do not help doctors work out if someone has simple steatosis or NASH, meaning that other specialist tests are needed.
Stage 3: fibrosis
Some people with NASH go on to develop fibrosis, which is where persistent inflammation in the liver results in the generation of fibrous scar tissue around the liver cells and blood vessels.
This fibrous tissue replaces some of the healthy liver tissue, but there is still enough healthy tissue for the liver to function normally.
Stage 4: cirrhosis
This is the most severe stage, where bands of scar tissue and clumps of liver cells develop. The liver shrinks and becomes lumpy (known as cirrhosis).
Cirrhosis tends to occur after the age of 50-60, following many years of liver inflammation associated with the early stages of the disease. However, this can happen much earlier in some people.
People who have type 2 diabetes are at the greatest risk of developing cirrhosis of the liver caused by NAFLD.
The damage caused by cirrhosis is permanent and can't be reversed. Cirrhosis progresses slowly, over many years, gradually causing your liver to stop functioning. NAFLD can also lead to primary liver cancer(hepatocellular carcinoma). This is what is known as liver failure. Learn more about cirrhosis of the liver, including the warning signs.
Who is affected?
You are more likely to develop NAFLD and more severe forms of the disease, such as NASH, fibrosis or cirrhosis if you:
are obese or overweight
have type 2 diabetes (this causes an increased uptake of fat into the liver cells)
have high blood pressure
have high cholesterol
are over the age of 50
Living with NAFLD
Most people with NAFLD do not develop serious liver problems and just have stage 1 of the disease (simple fatty liver).
Simple fatty liver may go away if the underlying cause is tackled. For example, losing excess weight or controlling diabetes better can make fatty liver disappear.
Many people do not have symptoms, although it's common to feel tired and some people have a persistent pain in the upper right part of their abdomen (where their liver is).
It can take years for symptoms of fibrosis or cirrhosis to appear. It is important to make lifestyle changes to prevent the disease progressing to a more serious stage and to lower your risk of having a heart attack or stroke.
Losing weight and exercising
The most important thing that people with NAFLD can do is to go on a gradual weight loss programme and exercise regularly. This helps in by:
reducing the amount of fat in your liver cells – this helps to heal inflammation
lowering your risk of stroke and heart attack
Losing weight is particularly important if you have type 2 diabetes, but is important for everyone with NAFLD.
If you smoke, it's really important to give up, as this will also help to reduce your risk of heart attack and stroke. Take steps now to stop smoking.
If you have high blood pressure or cholesterol, you may need medical treatment for these. Read about the treatment of high blood pressureand treatment of high cholesterol.
If you have type 2 diabetes, you may need medicines that reduce high blood sugar levels. At first, this will usually be in the form of tablets, and sometimes a combination of more than one type of tablet. It may also include injections of insulin. Learn more about the medical treatment of type 2 diabetes.
There are currently no specific medicines for NAFLD, but certain medicines used to treat high blood pressure and diabetes also have a beneficial effect on the liver. Your doctor may prescribe a particular medicine to help reduce the chance of NAFLD causing cirrhosis or liver cancer.
NAFLD is not caused by alcohol, but it may make the condition worse. It's therefore advisable to stop drinking alcohol. Read our tips on cutting down alcohol consumption.
Role of the liver
The liver has many important functions, which keep the body working normally. These include:
storing glycogen, which is broken down in to glucose (sugar) and released into the bloodstream when the body needs energy
helping to process fats and proteins
making proteins that enable the blood to clot
helping to remove or process alcohol, drugs and toxins
making bile, which is a fluid that passes through the bile duct to the gut. This is needed to break down digested food into fats