Nonalcoholic steatohepatitis (NASH) develops when the body stores excess fat in the liver cells, making it difficult for the liver to function. This causes swelling and damage, which can become serious.

NASH is one of two types of non-alcohol-related fatty liver disease (NAFLD).

The National Institutes of Health (NIH) estimate that between 1.5% and 6.5% of adults in the United States have NASH.

In this article, we describe what NASH is, what symptoms it causes, how doctors diagnose and treat it, and the outlook for someone who has it.

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NASH is a potentially serious form of liver disease that develops in people who drink little or no alcohol.

The acronym stands for “nonalcoholic steatohepatitis.” Doctors diagnose steatosis, also called fatty liver, if more than 5% of the liver’s weight is fat.

If someone has NASH, their liver has a high percentage of fat, but it is also swollen has sustained damage, which can cause fibrosis, or scarring.

If this scarring is very significant, it may lead to cirrhosis, a condition that causes permanent liver damage.

NASH is a type of NAFLD, which may be the most common chronic liver disease in industrialized nations, including the U.S. As many as 25% of U.S. adults may have NAFLD. Among this group, about 80% have simple fatty liver disease and the others have NASH.

Most people with NASH and other forms of NAFLD have no symptoms. Those who do develop symptoms may feel tired or have pain in the upper right side of the abdomen.

Children with NASH may experience:

  • fatigue
  • pain in the middle or upper-right part of the abdomen
  • patches of darker, discolored skin, usually on the neck or under the arms

A doctor may only diagnose NASH after many years, when cirrhosis occurs. Anyone who develops any of the following symptoms should contact a doctor:

  • behavioral changes such as slurred speech or confusion
  • easy bruising and bleeding
  • spider veins just under the skin
  • intense itchiness
  • a swollen belly
  • yellowing of the whites of the eyes, and in some people, the skin

Receiving appropriate care is key. If a person with NASH develops cirrhosis, this increases the risk of developing hepatocellular carcinoma, a common type of liver cancer.

While the cause of NASH is unclear, ongoing research suggests that the following may play a role:

  • oxidative stress, an imbalance between the production of free radicals and antioxidants
  • apoptosis, or programmed cell death, of liver cells
  • intestinal bacteria, which may cause inflammation of the liver
  • overproduction and release of cytokines, types of toxic inflammatory protein that the body produces
  • a person’s genetic makeup

While the exact causes of NASH are currently unclear, the following can increase a person’s risk of developing it:

As people with NASH do not usually experience symptoms, doctors often recognize signs of fatty liver during screening for other conditions or routine blood tests.

High levels of the enzymes alanine aminotransferase and aspartate aminotransferase are markers of liver inflammation. If a blood tests shows this, a doctors orders more tests to rule out other liver diseases.

These blood tests do not show whether there is scarring, however, or the extent of liver damage. So doctors then order imaging tests, such as ultrasound scans, that can show how stiff the liver is. Magnetic resonance elastography (MRE) tests combine features of ultrasound and MRI imaging to show the extent of scarring.

Occasionally, doctors then order a liver biopsy to confirm the diagnosis. This involves removing a small sample of liver tissue for microscopic examination.

Because biopsies are invasive and costly, and many doctors only recommend them if other tests show significant scarring and the doctors suspect cirrhosis.

There are no specific medical treatments for NASH. Taking the following steps can help prevent further damage:

  • maintaining a moderate weight, and if this involves losing weight, doing so gradually
  • having a balanced, healthy diet with low amounts of processed foods and fats, and little, if any, fructose
  • getting regular exercise
  • limiting or avoiding alcohol
  • controlling blood cholesterol levels
  • managing diabetes, for anyone who has it

If a person with NASH also has cirrhosis, the treatment may include medications and possibly surgery.

People with NASH who develop liver cancer or liver failure may require a transplant.

A person with NASH has a high percentage of fat in their liver. The liver is also swollen and has sustained damage. This damage can cause fibrosis, or scarring.

In some people, the scarring and damage become permanent, and doctors diagnose cirrhosis. At this stage, the liver may not be able to function properly. Some people may go on to develop liver cancer. In either case, a liver transplant may be necessary.

NASH involves swelling, damage, and a high percentage of fat in the liver. It can become severe and lead to permanent damage. It also increases the risk of a common type of liver cancer.

There are currently no medical treatments for NASH, but self-care strategies and lifestyle changes can help manage it. If cirrhosis develops, the treatment may involve medications and surgery. If liver failure or cancer develops, a person may need a transplant.