Difference between fatty liver disease, NAFLD, & NASH.

What is fatty liver disease?

We start of with fat and the relation of our liver. Normally there should be little or ideally no fat in a healthy liver. Having little fat in our liver often makes no harm. Fatty liver is the name given to a condition in which you have too much fat in your liver. This is caused by the build-up of fats called triglycerides. These are the most common fats in our bodies. They belong to a group of fatty, waxy substances called lipids that your body needs for energy and cell growth.

We get triglycerides from our diet and they are also made in the liver. The liver processes triglycerides and controls their release. It combines them with special proteins to form tiny spheres called lipoproteins which it sends into the bloodstream to circulate among the cells of your body. When this process is interrupted and the flow of triglycerides to the liver is increased, their release, or ‘secretion’, from the liver is slowed down. This is what leads to the build-up of fat in your liver cells. Fatty liver diseases is found more common in western countries, most people with fatty liver disease do not develop serious liver problems. But if left untreated, fatty liver diseases can developed into N.A.S.H- Non alcoholic steatohepatitis and cirrhosis.

Until recently fatty liver was considered relatively harmless. It was not thought to progress to chronic (long-term) or serious liver disease.

Today it is one of the most common forms of liver disease and is known to lead to advanced conditions. In the majority of cases fatty liver does not cause any harm but for an increasing number of people the effects of having fat in their liver over a long period may lead to inflammation causing swelling and tenderness (hepatitis) and then to scarring (fibrosis).

In some people, this can progress to a condition known as cirrhosis, which can be life- threatening. Fatty liver disease and NASH can also let to liver cirrhosis.

Clinical knowledge about fatty liver is still coming together but common risk factors are obesity, diabetes and drinking too much alcohol. While the relationship between these factors is not fully known, they can be considered triggers for progression to other types of liver disease.

If alcohol is the cause of fatty liver it is called alcoholic liver disease (ALD). This leaflet is for people worried about fatty liver that is not caused by alcohol. This is known as non alcoholic fatty liver disease (NAFLD).

What is non-alcoholic fatty liver disease?

Non-alcoholic fatty liver disease (NAFLD) describes a range of conditions caused by a build-up of fat within liver cells. It is helpful to divide NAFLD into four stages:

Simple fatty liver – also called hepatic steatosis. Normally, very little fat is stored in liver cells. Simple fatty liver means that excess fat accumulates in liver cells. For most people, simple fatty liver does not cause any harm or problems to the liver. However, in some people it can progress to more severe forms of NAFLD.

Non-alcoholic steatohepatitis – often called NASH. In this condition the excess fat in the liver cells is associated with, or may cause, inflammation of the liver. (Steato means fat, and hepatitis means inflammation of the liver). This is much less common than simple fatty liver.

Fibrosis: any form of persistent hepatitis, including steatohepatitis, may eventually cause scar tissue (fibrosis) to form within the liver. When fibrosis first develops often there are many liver cells that continue to function quite well.

Cirrhosis. Cirrhosis is a serious condition where normal liver tissue is replaced by a lot of fibrosis. The structure and function of the liver are badly disrupted. It is, in effect, like a severe form of liver fibrosis. Many liver conditions can lead to cirrhosis, including NAFLD. Severe cirrhosis can lead to liver failure. (See separate leaflet called ‘Cirrhosis’).

NAFLD occurs in people who do not drink excessive amounts of alcohol and so alcohol is not the cause. Most people with NAFLD have simple fatty liver. Only a minority progress to develop NASH. And, only a minority of people with NASH progress to cirrhosis. It is not clear why some people with simple fatty liver progress to the more severe forms of NAFLD, and most do not.

Non alcoholic steatohepatitis (NASH)

Non alcoholic steatohepatitis (NASH) is a more advanced form of NAFLD in which there is inflammation in and around the fatty liver cells. This may cause swelling of your liver and discomfort or pain around it. If you place your right hand over the lower right hand side of your ribs it will cover the area of your liver.

With intense, on-going inflammation a build up of scar tissue may form in your liver. This process is known as fibrosis, and can lead to cirrhosis. NASH is now considered to be one of the main causes of cirrhosis.

Cirrhosis is usually the result of long-term, continuous damage to the liver. This is where irregular bumps, known as nodules, replace the smooth liver tissue and the liver becomes harder. The effect of this, together with continued scarring from fibrosis, means that the liver will run out of healthy cells to support normal functions. This can lead to complete liver failure.

NASH should be distinguished from acute fatty liver disease, which may occur during pregnancy or with certain drugs or toxins (poisons). This condition is very rare and may lead rapidly to liver failure.

What is the difference between NAFLD and NASH?

Non alcoholic fatty liver disease (NAFLD)

NAFLD is actually a term for a wide range of conditions characterised by the build-up of fat in the liver cells of people who do not drink alcohol excessively.

At one end of this range is simple fatty liver, or steatosis. This is the stage where fat is first detected in the liver cells and is generally regarded as benign (harmless).

Non alcoholic steatohepatitis (NASH) is a significant development in NAFLD. This is a more aggressive condition that may cause scarring to the liver and can progress to cirrhosis. Cirrhosis causes irreversible damage to the liver and is the most severe stage in NAFLD.

In simple terms it may be easiest to think of NAFLD as having the following stages:

1. fatty liver

2. a form of hepatitis known as non alcoholicsteatohepatitis (NASH)

3. fibrosis

4. cirrhosis