Nonalcoholic fatty liver disease happens when there is too much fat in the liver, or steatosis. The condition is also known as fatty liver.

There may be no symptoms in the early stages, but continued damage to the liver can lead to a more severe condition.

Some people with nonalcoholic fatty liver disease (NAFLD) will develop nonalcoholic steatohepatitis (NASH). This can develop into cirrhosis, or scarring and dysfunction of the liver.

Fatty liver is often related to obesity, high blood pressure, diabetes, and high cholesterol. NAFLD or NASH is not due to high alcohol consumption.

Around 10 to 46 percent of people in the United States have fatty liver but no inflammation or damage. Between 3 and 12 percent have NASH. NAFLD is the most common cause of liver disease in western countries.

Fatty liver can also occur during pregnancy, and cirrhosis can result from alcohol-related liver disease, but NAFLD is considered a separate diagnosis and doctors manage it differently.

Fast facts about fatty liver disease

  • Nonalcoholic fatty liver disease (NAFLD) can occur if too much fat builds up in the liver.
  • Many people have a fatty liver with no symptoms, but, in some cases, it can progress to a more serious condition.
  • The exact cause is unknown, but obesity appears to be a risk factor.
  • Following a healthy, balanced diet that is low in sugar and trans fats may help prevent or even reverse the condition.
  • People with any type of liver disease should avoid alcohol or consume only very small amounts.

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Fatty liver disease often occurs with obesity, diabetes, and chronic kidney disease.

The liver is important for removing toxins from the body. If it does not work properly, various symptoms can arise.

If the body produces too much fat, or if the fat is not properly metabolized, it can build up in the liver.

If too much fat builds up in the liver, this can cause fatty liver. If fat continues to accumulate, this can lead, in some cases, to NASH and eventually cirrhosis and liver failure.

Fatty liver

At a threshold level, more than 5 to 10 percent of the liver weight is fat.

If more fat than this builds up in the liver, this is known as NAFLD, or simple fatty liver. It is not healthy, but it not necessarily severe enough to cause any problems, and the person will not usually notice any symptoms.

Most people with simple fatty liver will not know they have it. They may only find out after being tested for some other condition, or because other risk factors suggest that a test is a good idea.

Some 30 to 40 percent of adults in the U.S. have NAFLD. However, it is hard to establish an exact figure, as there is no one set of criteria for defining NAFLD.

For most people, the condition does not progress beyond this stage.

Nonalcoholic steatosis

If fat continues to build up and the liver becomes inflamed, NASH results. In the U.S., this affects between 3 and 12 percent of adults.

Around 75 percent of patients will have swelling in the liver, or hepatomegaly.

Symptoms may include:

  • tiredness and fatigue, including muscle weakness and a lack of energy
  • discomfort and possibly swelling in the upper abdomen
  • weight loss
  • low appetite
  • nausea

The symptoms can be vague, and they can resemble those of a number of other problems. Tests may be carried out to eliminate other conditions.

Scientists are unsure why some people are more likely to develop NASH.

Cirrhosis and liver failure

In time, 10 to 25 percent of people with NASH will develop scarring or fibrosis, also known as cirrhosis, and liver failure.

Symptoms include:

  • tiredness and weakness
  • nausea, vomiting, and diarrhea
  • tarry stools
  • abdominal swelling and pain
  • a yellowing of the skin and eyes, known as jaundice
  • confusion, difficulty focusing, memory loss, and hallucinations
  • itchy skin
  • bleeding and bruising easily

In severe cases, a liver transplant may be necessary.

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A person with diabetes may have a higher risk of developing NAFLD.

Exactly how and why fatty liver develops is not clear. It occurs when the body produces too much fat, or when it cannot process fat properly.

Obesity is a clear risk factor. Around 70 percent of people with obesity have the condition, while 10 to 15 percent of people with a normal weight have it.

Regardless of their weight, a person with “deep” abdominal fat is more likely to have a fatty liver.

Other risk factors include:

  • diabetes
  • high cholesterol or high levels of fat in the blood
  • high blood pressure
  • high blood fats, or triglycerides

People with metabolic syndrome, a condition that involves a clustering of the risk factors mentioned above, are at higher risk.

Between 40 and 80 percent of people with type 2 diabetes have NAFLD.

Researchers have found “growing evidence” that NAFLD is linked to cardiovascular disease (CVD) and chronic kidney disease (CKD).

This means that those with NAFLD are also more likely to have diabetes and heart disease.

While there are clear links between obesity and fatty liver, some people develop NAFLD without obesity. This suggests that there are other factors.

These include:

  • genetic influences
  • smoking
  • older age
  • certain medications, such as steroids, and tamoxifen for cancer treatment
  • rapid weight loss
  • infections, such as hepatitis
  • exposure to some toxins

However, research suggests that “excess fat mass remains the most common background condition.”

NAFLD is also the most common form of long-term liver disease in children. A review published in 2016 states that it affects between 10 and 20 percent of pediatric patients and 50 to 80 percent of children with obesity.

The scientists predict:

Within the next 10 years, it is expected to become the leading cause of liver pathology, liver failure, and indication for liver transplantation in childhood and adolescence in the Western world.”

Around 25 percent of pediatric patients with NASH will go on to develop cirrhosis within 10 years. Among those with obesity, the risk is higher.

Early stage NAFLD does not usually produce symptoms, so diagnosis usually happens because of a routine blood test or because the person has the relevant risk factors.

If the doctor suspects NAFLD, they will feel the abdominal area, to find out if there is any swelling. They will ask about diet and lifestyle and any use of medications, supplements, and alcohol.

If tests suggest that there is damage to the liver or that the liver is swollen, the doctor must rule out other possible conditions, including alcoholic liver disease.

Imaging scans, such as ultrasound, CT, and MRI can show up fat in the liver.

A biopsy can confirm NAFLD, reveal the extent of the damage, and distinguish it from other types of liver problem. The doctor will use a needle to take a small tissue sample from the liver.

There is no medical treatment for fatty liver, but lifestyle choices, such as achieving or maintaining a healthy weight, can reduce the risk and possibly reverse the damage, in the early stages.

Dietary tips

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A diet that contains plenty of fresh food can help prevent liver damage.

To reduce the risk of NAFLD, it is best to:

  • follow a balanced diet with moderate portions
  • eat plenty of fruits and vegetables
  • consume both proteins and carbohydrates, but limit fats and sugars
  • reduce salt intake
  • replace saturated and trans fats with monounsaturated and polyunsaturated fats

The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) recommend the following dietary tips:

  • replace trans fats and animal fats with olive oil, flaxseed oil, corn, soybean, and safflower oils
  • eat oily fish instead of meat
  • avoid foods that are high in simple sugars, such as fructose, found in sweetened drinks, sports drinks, and juices
  • eat more foods that are low on the glycemic index (GI), such as fruits, vegetables, and whole grains
  • eat fewer high-GI foods, such as white bread and white rice
  • avoid alcohol or drink in moderation

Scientists are looking at whether vitamin E may help, but more research is needed. Those who ae considering taking supplements or herbal remedies should always speak to a doctor first.

A healthy diet and regular exercise will reduce the risk of a wide range of conditions, including diabetes and cardiovascular disease.

For most people, a fatty liver does not usually cause serious problems. To some extent, the liver can repair itself, so switching to a healthy lifestyle will help.

Researchers warn that NAFLD is on the increase, and if obesity continues to rise, it could become “an epidemic.”

Although simple fatty liver is not dangerous, without preventive action, some people will go on to develop NASH, and between 10 and 25 percent of adults with NASH will go on to develop cirrhosis within 10 years.

In the U.S., fatty liver disease is the third cause of liver transplant, and it is on the rise.

In addition, NAFLD is linked to CVD, CKD, and other conditions. Whether or not these can be reversed, even if the liver recovers, is not clear.

The best way to treat and prevent it is through healthful lifestyle choices, with a varied and balanced diet and regular exercise.