Nonalcoholic Fatty Liver Disease (NAFLD) & NASH

Definition & Facts

Nonalcoholic fatty liver disease (NAFLD) is a condition in which fat builds up in your liver. Nonalcoholic fatty liver (NAFL) and nonalcoholic steatohepatitis (NASH) are types of NAFLD. If you have NASH, you have inflammation and liver damage, along with fat in your liver.

Symptoms & Causes

Usually, nonalcoholic fatty liver disease (NAFLD) is a silent disease with few or no symptoms. Certain health conditions—including obesity, metabolic syndrome, and type 2 diabetes—make you more likely to develop NAFLD.

Diagnosis

Doctors use your medical history, a physical exam, and tests to diagnose nonalcoholic fatty liver disease (NAFLD). Doctors may use blood tests, imaging tests, and liver biopsy to diagnose NAFLD and tell the difference between nonalcoholic fatty liver (NAFL) or nonalcoholic steatohepatitis (NASH).

Treatment

Doctors recommend weight loss to treat nonalcoholic fatty liver disease (NAFLD), which is either nonalcoholic fatty liver (NAFL) or nonalcoholic steatohepatitis (NASH). Weight loss can reduce fat, inflammation, and fibrosis in the liver. No medicines have been approved to treat NAFLD or NASH.

Eating, Diet, & Nutrition

You may be able to prevent nonalcoholic fatty liver disease (NAFLD)—nonalcoholic fatty liver (NAFL) or nonalcoholic steatohepatitis (NASH)—by eating a healthy diet and maintaining a healthy weight. If you have NAFLD, your doctor may recommend weight loss and diet changes.

Definition & Facts of NAFLD & NASH

In this section:

What is NAFLD?

Nonalcoholic fatty liver disease (NAFLD) is a condition in which excess fat is stored in your liver. This buildup of fat is not caused by heavy alcohol use. When heavy alcohol use causes fat to build up in the liver, this condition is called alcohol-associated liver disease.

Two types of NAFLD are nonalcoholic fatty liver (NAFL) and nonalcoholic steatohepatitis (NASH). People typically develop one type of NAFLD or the other, although sometimes people with one form are later diagnosed with the other form of NAFLD.

NAFL

NAFL is a form of NAFLD in which you have fat in your liver but little or no inflammation or liver damage. NAFL typically does not progress to cause liver damage or complications. However, NAFL can cause pain from enlargement of the liver.

NASH

NASH is the form of NAFLD in which you have inflammation of the liver and liver damage, in addition to fat in your liver. The inflammation and liver damage of NASH can cause fibrosis, or scarring, of the liver. NASH may lead to cirrhosis, in which the liver is scarred and permanently damaged. Cirrhosis can lead to liver cancer NIH external link.

Experts are not sure why some people with NAFLD have NASH while others have NAFL.

How common is NAFLD?

NAFLD is one of the most common causes of liver disease in the United States. The majority of people with NAFLD have NAFL. Only a small number of people with NAFLD have NASH. Experts estimate about 24% of U.S. adults have NAFLD and about 1.5% to 6.5% of U.S. adults have NASH.¹

Who is more likely to develop NAFLD?

NAFLD is more common in people who have certain conditions, including obesity and conditions that may be related to obesity, such as type 2 diabetes. Studies suggest that one-third to two-thirds of people with type 2 diabetes have NAFLD.¹ Research also suggests that NAFLD is present in up to 75% of people who are overweight and in more than 90% of people who have severe obesity, also called extreme obesity.^{2, 3}

NAFLD can affect people of any age, including children. Research suggests that close to 10% of U.S. children ages 2 to 19 have NAFLD.⁴ However, people are more likely to develop NAFLD as they age.

While NAFLD occurs in people of all races and ethnicities, it is most common among Hispanic individuals, followed by non-Hispanic whites and Asian Americans, including those of East Asian and South Asian descent.^5,6 NAFLD is less common among non-Hispanic Blacks.⁵ On average, Asian Americans with NAFLD have a lower BMI than non-Hispanic whites with NAFLD.⁶ Experts think that genes may help explain some of the racial and ethnic differences in NAFLD.

What are the complications of NAFLD?

People with NAFLD may develop liver complications or other health problems.

Liver complications

People with NAFL typically don’t develop liver complications, although they have a higher risk for other health problems.¹

People with NASH can develop liver complications, such as cirrhosis and liver cancer. If cirrhosis leads to liver failure, you may need a liver transplant. People with NASH have an increased chance of dying from liver-related causes.⁵

Symptoms & Causes of NAFLD & NASH

What are the symptoms of NAFLD?

Usually, nonalcoholic fatty liver disease (NAFLD)—including nonalcoholic fatty liver (NAFL) and nonalcoholic steatohepatitis (NASH)—is a silent disease with few or no symptoms. You may not have symptoms even if you develop cirrhosis due to NASH.

If you do have symptoms, you may feel tired or have discomfort in the upper right side of your abdomen.

What causes NAFLD?

Experts are still studying the causes of NAFLD. Research suggests that certain health conditions, your genes, and diet and the digestive system may make you more likely to develop NAFLD.

Health conditions

You are more likely to develop NAFLD if you have the following health conditions

overweight or obesity
insulin resistance or type 2 diabetes
abnormal levels of fats in your blood, which may include
- high levels of triglycerides
- abnormal levels of cholesterol—high total cholesterol, high LDL cholesterol, or low HDL cholesterol
metabolic syndrome or one or more traits of metabolic syndrome. Metabolic syndrome is a group of traits and medical conditions linked to overweight and obesity. Doctors define metabolic syndrome as the presence of any three of the following
- large waist size
- high levels of triglycerides in your blood
- low levels of HDL cholesterol in your blood
- high blood pressure
- higher than normal blood glucose levels or a diagnosis of type 2 diabetes

Having more of these health conditions increases your chances of developing NASH. Losing weight may cause NASH to switch to NAFL, and regaining weight may cause NAFL to switch to NASH.

Genes

Researchers have found that certain genes may make you more likely to develop NAFLD. These genes may help explain why NAFLD is more common in certain racial and ethnic groups. Experts are still studying the genes that may play a role in NAFLD.

Diet and the digestive system

Researchers are studying whether diets high in fructose—a sugar that is part of table sugar and is also commonly added to sweeten drinks and foods—may increase the risk of NAFLD.

Scientists have also examined the relationship between NAFLD and the microbiome—the bacteria in your digestive tract that help with digestion. Studies have found differences between the microbiomes of people who have NAFLD and those who don’t. Experts are still studying how the microbiome may affect NAFLD.

Is NAFLD the only cause of fatty liver?

Fatty liver may have causes other than NAFLD. If medical tests suggest you have a buildup of fat in your liver, your doctor may ask questions or order tests for other causes.

Alcohol-associated liver disease

Fat may build up in the liver due to alcohol-associated liver disease—damage to the liver and its function due to excessive alcohol consumption NIH external link. If you have a history of heavy alcohol use and fat in your liver, your doctor may determine you have alcohol-associated liver disease instead of NAFLD.

If you have risks for NAFLD and also drink excessively, you could have both NAFLD and alcohol-associated liver disease at the same time. No tests can easily tell how much each plays a role.

Other causes

Other causes of excess fat in the liver include

disorders, called lipodystrophies, that cause your body to use or store fat improperly
rapid weight loss or malnutrition
some medicines, including corticosteroids NIH external link, HIV treatment External link, estrogens NIH external link, certain medicines used to treat cancer, and others
exposure to some toxins
rare genetic diseases, such as Wilson disease and hypobetalipoproteinemia

Diagnosis of NAFLD & NASH

How do doctors diagnose NAFLD?

Doctors use your medical history, a physical exam, and tests to diagnose nonalcoholic fatty liver disease (NAFLD)—including nonalcoholic fatty liver (NAFL) and nonalcoholic steatohepatitis (NASH).

Medical history

Your doctor will ask if you have a history of health conditions that make you more likely to develop NAFLD, such as

overweight or obesity
insulin resistance or type 2 diabetes
high levels of triglycerides or abnormal levels of cholesterol in your blood
metabolic syndrome

Your doctor will ask about diet and lifestyle factors that may make you more likely to develop NAFLD, such as a lack of physical activity, eating a diet high in sugar, or drinking sugary beverages.

Your doctor will also ask about other causes of liver disease or fat in your liver. Your doctor will ask about your alcohol intake to find out whether fat in your liver is a sign of alcohol-associated liver disease or NAFLD.

Physical exam

During a physical exam, a doctor usually examines your body and checks your weight and height to calculate your body mass index. Your doctor will look for signs of NAFL or NASH, such as

an enlarged liver
signs of insulin resistance, such as darkened skin patches over your knuckles, elbows, and knees
signs of cirrhosis, such as an enlarged spleen, ascites, and muscle loss

What tests do doctors use to diagnose NAFLD?

Doctors use blood tests, imaging tests, and sometimes liver biopsy to diagnose NAFLD and to tell the difference between NAFL and NASH.

Blood tests

A health care professional may take a blood sample from you and send the sample to a lab. Your doctor may suspect you have NAFLD if your blood test shows increased levels of the liver enzymes alanine aminotransferase (ALT) and aspartate aminotransferase (AST).

Your doctor may use the results of routine blood tests to calculate special scores, such as the FIB-4 or APRI. These scores can help doctors identify or rule out advanced liver fibrosis, or scarring.

Your doctor may perform additional blood tests to find out if you have other health conditions that may increase your liver enzyme levels.

Imaging tests

Routine imaging tests can show fat in your liver. These tests can’t show inflammation or fibrosis, so your doctor can’t use these tests to find out whether you have NAFL or NASH. If you have cirrhosis, routine imaging tests may show nodules, or lumps, in your liver.

Your doctor may use the following imaging tests to help diagnose NAFLD

ultrasound NIH external link, which uses a device called a transducer that bounces safe, painless sound waves off your organs to create an image of their structure
computed tomography (CT) scan NIH external link, which uses a combination of x-rays and computer technology to create images of your liver
magnetic resonance imaging (MRI) NIH external link, which uses radio waves and magnets to produce detailed images of organs and soft tissues without using x-rays

Elastography NIH external link is a newer type of imaging test that can help determine if you have advanced liver fibrosis. In some cases, doctors may order elastography tests to measure the stiffness of your liver. Increased liver stiffness may be a sign of fibrosis. Commonly used types of elastography are

vibration-controlled transient elastography, a special type of ultrasound
sheer wave elastography, another type of ultrasound to detect increased liver stiffness
magnetic resonance elastography, a special type of MRI to measure liver stiffness

Liver biopsy

Liver biopsy is the only test that can prove a diagnosis of NASH and show clearly how severe the disease is. Liver biopsy can show fibrosis at earlier stages than elastography can. However, doctors don’t recommend liver biopsy for everyone with suspected NAFLD. Your doctor may recommend a liver biopsy if you are more likely to have NASH with advanced fibrosis or if your other tests show signs of advanced liver disease or cirrhosis. In some cases, doctors may recommend a liver biopsy to rule out other liver diseases.

During a liver biopsy, a doctor will take small pieces of tissue from your liver. A pathologist will examine the tissue under a microscope to look for signs of damage or disease.

Treatment for NAFLD & NASH

How do doctors treat NAFLD?

Doctors recommend weight loss to treat nonalcoholic fatty liver disease (NAFLD), either nonalcoholic fatty liver (NAFL) or nonalcoholic steatohepatitis (NASH). Weight loss can reduce fat, inflammation, and fibrosis—or scarring—in the liver.

If you are overweight or have obesity, losing weight by making healthy food choices, limiting portion sizes, and being physically active can improve NAFLD—either NAFL or NASH. Losing at least 3% to 5% of your body weight can reduce fat in the liver.⁵ You may need to lose up to 7% to 10% of your body weight to reduce liver inflammation and fibrosis.⁵ Physical activity alone, even without weight loss, is also beneficial.

Doctors recommend gradually losing weight to improve NAFLD. Rapid weight loss and malnutrition can make liver disease worse.

Medicines

No medicines have been approved to treat NAFLD—either NAFL or NASH. However, researchers are studying medicines that may improve these conditions.

For safety reasons, talk with your doctor before using dietary supplements NIH external link, such as vitamins, or any complementary or alternative NIH external link medicines or medical practices. Some herbal remedies NIH external link can actually damage your liver.

How do doctors treat the complications of NASH?

If NASH leads to cirrhosis, doctors can treat many complications of cirrhosis with medicines, minor medical procedures, and surgery. People with liver failure or liver cancer may need a liver transplant to restore health.

How can I prevent NAFLD?

You may be able to prevent NAFLD by being physically active regularly, eating a healthy diet, limiting your portion sizes, and maintaining a healthy weight.

Eating, Diet, & Nutrition for NAFLD & NASH

How can my diet help prevent or treat NAFLD?

If you don’t have nonalcoholic fatty liver disease (NAFLD)—nonalcoholic fatty liver (NAFL) or nonalcoholic steatohepatitis (NASH)—you may be able to prevent these conditions by eating a healthy diet, limiting your portion sizes, and maintaining a healthy weight.

If you have NAFLD, your doctor may recommend gradually losing weight if you are overweight or have obesity.

Your doctor may suggest changes to your diet such as

limiting your intake of fats, which are high in calories and increase your chance of developing obesity.
replacing saturated fats and trans fats in your diet with unsaturated fats, especially omega-3 fatty acids, which may reduce your chance of heart disease if you have NAFLD.
eating more low-glycemic index foods—such as most fruits, vegetables, and whole grains. These foods affect your blood glucose less than high-glycemic index foods, such as white bread, white rice, and potatoes.
avoiding foods and drinks that contain large amounts of simple sugars, especially fructose. Fructose is found in sweetened soft drinks, sports drinks, sweetened tea, and juices. Table sugar, called sucrose, is rapidly changed to glucose and fructose during digestion and is therefore a major source of fructose.

If you have NAFLD, you should minimize alcohol use, which can further damage your liver.

References

[1] Younossi ZM, Koenig AB, Abdelatif D, Fazel Y, Henry L, Wymer M. Global epidemiology of nonalcoholic fatty liver disease—meta-analytic assessment of prevalence, incidence, and outcomes. Hepatology. 2016;64(1):73–84. doi:10.1002/hep.28431

[2] Cotter TG, Rinella M. Nonalcoholic fatty liver disease 2020: the state of the disease. Gastroenterology. 2020;158(7):1851–1864. doi:10.1053/j.gastro.2020.01.052

[3] Machado M, Marques-Vidal P, Cortez-Pinto H. Hepatic histology in obese patients undergoing bariatric surgery. Journal of Hepatology. 2006;45(4):600–606. doi: 10.1016/j.jhep.2006.06.013.

[4] Schwimmer JB, Deutsch R, Kahen T, Lavine JE, Stanley C, Behling C. Prevalence of fatty liver in children and adolescents. Pediatrics. 2006;118(4):1388–1393. doi: 10.1542/peds.2006-1212

[5] Chalasani N, Younossi Z, Lavine JE, et al. The diagnosis and management of nonalcoholic fatty liver disease: practice guidance from the American Association for the Study of Liver Diseases. Hepatology. 2018;67(1):328–357. doi:10.1002/hep.29367

[6] Golabi P, Paik J, Hwang JP, Wang S, Lee HM, Younossi ZM. Prevalence and outcomes of non-alcoholic fatty liver disease (NAFLD) among Asian American adults in the United States. Liver International. 2019;39(4):748–757. doi:10.1111/liv.14038

Last Reviewed April 2021

Source of the above information: NIH/NIDDK

For more information, please visit https://www.niddk.nih.gov/health-information/liver -disease/nafld-nash

Disclaimer: The information provided on this website is for informational purposes only and is not intended to take the place of consultation with your physician.

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