Nonalcoholic steatohepatitis (NASH) is a form of non-alcohol-related fatty liver disease. It is a chronic condition that can cause lasting damage to the liver.

Non-alcohol-related fatty liver disease is the most common chronic liver disease, affecting almost 25% of people worldwide.

This “disease” is actually an umbrella term for several liver diseases that share characteristics, including the accumulation of fat in the liver — when heavy alcohol consumption is not the cause.

NASH is a progressive, serious form of non-alcohol-related fatty liver disease. In a person with NASH, the accumulation of fat in the liver occurs with inflammation and potentially scarring. NASH occurs in about 25% of non-alcohol-related fatty liver disease cases.

The disorder can be difficult to diagnose, as it may cause symptoms that are common to other conditions or no symptoms at all.

In this article, we describe the risk factors and treatments for NASH, as well as the symptoms that it can cause.

A person on an early morning hike up a mountainside.Share on Pinterest
Thomas Barwick/Getty Images

NASH is a serious, progressive form of non-alcohol-related fatty liver disease. It involves the accumulation of fat and inflammation in the liver. This inflammation can lead to scarring of liver tissue, which is called fibrosis.

Over time, this scarring can worsen. The damage may progress and lead to cirrhosis. This means that scar tissue replaces healthy tissue, and it increases the risk of liver failure.

The exact causes of non-alcohol-related fatty liver disease are not well understood. However, as research from 2021 confirms, a sedentary lifestyle and unhealthy diet can increase the chances of it developing.

These lifestyle and dietary factors can also cause obesity, another risk factor for non-alcohol-related fatty liver disease, which affects up to 80% of people with obesity.

NASH, more specifically, may result from metabolic syndrome, which includes a set of risk factors for heart disease and type 2 diabetes.

Signs of metabolic syndrome can include:

People with NASH may have no symptoms, and a person may be unaware that they have it, which is part of the reason that NASH is so dangerous.

If a person has symptoms, they may experience vague discomfort or stiffness in the upper-right area of their abdomen or other general symptoms, such as fatigue.

Doctors can test for other liver diseases and signs of liver damage. These tests can rule out other conditions and ultimately lead to a NASH diagnosis.

A doctor can then use various staging tools to identify the severity of non-alcohol-related fatty liver disease or NASH specifically.

The stages of non-alcohol-related fatty liver disease include:

  • Stage 1: The liver cells are starting to accumulate fat.
  • Stage 2: There are also signs of inflammation. NASH begins at this stage.
  • Stage 3: There are signs of fibrosis. The liver can still function, but scar tissue may gradually replace healthy tissue.
  • Stage 4: This is late stage fibrosis or cirrhosis. Scar tissue and damage from inflammation is widespread, and the liver cannot function properly.

Doctors may also use a fibrosis-4 calculator to determine the amount of scar tissue in the liver. The scores are:

  • F0: no fibrosis
  • F1: portal fibrosis without septa, which are tissue changes that show advancing liver damage
  • F2: portal fibrosis with septa
  • F3:numerous septa but no cirrhosis
  • F4: cirrhosis

The staging techniques described above help doctors identify the severity of non-alcohol-related fatty liver disease. Arriving at these scores may require multiple tissue biopsies from different areas of the liver.

Doctors may also use imaging tests, such as ultrasounds or MRIs, to visualize the changes to the liver, including scarring and other damage.

Undergoing testing to determine the extent of any damage is crucial for people with liver disease. Research from 2021 reports that fibrosis is the best predictor of death in people with non-alcohol-related fatty liver disease. This is why doctors stage and classify the damage so thoroughly before recommending a tailored treatment approach.

There are no approved drug-based treatments for NASH. The scar tissue in the liver does not respond well to known medical treatments. Research into different therapeutic approaches to NASH is underway.

To slow, and potentially reverse, liver damage, a doctor recommends significant changes to the person’s lifestyle and diet.

Treatment guidelines from 2021 confirm that diet and lifestyle changes are the most effective treatment for NASH. They recommend:

  • having a healthy diet
  • doing at least 150–200 minutes of moderate-intensity aerobic exercise each week
  • reaching and maintaining a healthy weight
  • avoiding alcohol and smoking
  • effectively managing other illnesses, such as diabetes or heart disease

Doctors may also recommend some supplements, such as vitamin E, which may reduce inflammation in the liver.

Anyone who has symptoms of a metabolic disorder should see a doctor. However, there may be no symptoms of NASH or liver disease in general, so regular checkups are important for people with a higher risk.

Anyone with multiple risk factors or a family history of NASH or metabolic syndrome should receive a risk assessment and possibly tests to check their liver health.

NASH is a progressive, potentially dangerous form of non-alcohol-related fatty liver disease. Without treatment, the scarring and other damage may lead to liver failure and death.

People with NASH or any other form of non-alcohol-related fatty liver disease should follow their doctors’ recommendations about diet and lifestyle changes and take steps to manage any other health conditions that they have. Research from 2015 found that heart disease was the most common cause of death in people with non-alcohol-related fatty liver disease, making up 38% of cases.

The outlook for a person with NASH depends on factors such as the extent of liver damage, any accompanying conditions, and the changes to their lifestyle and diet. Making these changes and receiving treatment for any other health problems can improve the outlook.