Nonalcoholic Fatty Liver Disease & NASHReturn to Overview Page
Definition & Facts
In this section:
- What is NAFLD?
- How common are NAFLD and NASH?
- Who is more likely to develop NAFLD?
- What are the complications of NAFLD and NASH?
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 alcoholic liver disease.
Two types of NAFLD are simple fatty liver and nonalcoholic steatohepatitis (NASH). Simple fatty liver and NASH are two separate conditions. 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.
Simple fatty liver
Simple fatty liver, also called nonalcoholic fatty liver (NAFL), is a form of NAFLD in which you have fat in your liver but little or no inflammation or liver cell damage. Simple fatty liver typically does not progress to cause liver damage or complications.
NASH is a form of NAFLD in which you have hepatitis—inflammation of the liver—and liver cell damage, in addition to fat in your liver. Inflammation and liver cell damage can cause fibrosis, or scarring, of the liver. NASH may lead to cirrhosis or liver cancer .
Experts are not sure why some people with NAFLD have NASH while others have simple fatty liver.
How common are NAFLD and NASH?
NAFLD is one of the most common causes of liver disease in the United States. Most people with NAFLD have simple fatty liver. Only a small number of people with NAFLD have NASH. Experts estimate that about 20 percent of people with NAFLD have NASH.1
Between 30 and 40 percent of adults in the United States have NAFLD. About 3 to 12 percent of adults in the United States 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. Researchers have found NAFLD in 40 to 80 percent of people who have type 2 diabetes and in 30 to 90 percent of people who are obese.2 In research that tested for NAFLD in people who were severely obese and undergoing bariatric surgery, more than 90 percent of the people studied had NAFLD.3
NAFLD can affect people of any age, including children. Research suggests that close to 10 percent 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 in Hispanics, followed by non-Hispanic whites.2 NAFLD is less common in African Americans.2 Asian Americans are more likely than people of other racial or ethnic groups to develop NAFLD when their weight is within the normal range.5
What are the complications of NAFLD and NASH?
The majority of people with NAFLD have simple fatty liver, and people with simple fatty liver typically don’t develop complications.1
NASH can lead to complications, such as cirrhosis and liver cancer. People with NASH have an increased chance of dying from liver-related causes.3
Studies also suggest that people with NAFLD have a greater chance of developing cardiovascular disease. Cardiovascular disease is the most common cause of death in people who have either form of NAFLD.6
Symptoms & Causes
What are the symptoms of NAFLD and NASH?
Usually, nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) are silent diseases 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 and NASH?
Experts are still studying the causes of NAFLD and NASH. Research suggests that certain health conditions make you more likely to develop NAFLD or NASH.
Causes of NAFLD
You are more likely to develop NAFLD—either simple fatty liver or NASH—if you
- are overweight or obese
- have insulin resistance
- have abnormal levels of fats in your blood, which may include
- have 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. People with metabolic syndrome are more likely to develop type 2 diabetes and heart disease. Experts think NAFLD may be closely linked to metabolic syndrome. Doctors define metabolic syndrome as the presence of any three of the following:
- have type 2 diabetes
Research also suggests that certain genes may make you more likely to develop NAFLD. Experts are still studying the genes that may play a role in NAFLD.
In NAFLD, people have a buildup of fat in the liver that is not caused by alcohol use. If you have a history of heavy alcohol use and fat in your liver, your doctor may determine that you have alcoholic liver disease instead of NAFLD.
Causes of NASH
Experts are not sure why some people with NAFLD have NASH and others have simple fatty liver. Research suggests that certain genes may play a role.
People with NAFLD are more likely to have NASH if they have one or more of the following conditions:
- obesity, especially with a large waist size
- high blood pressure
- high levels of triglycerides or abnormal levels of cholesterol in their blood
- type 2 diabetes
- metabolic syndrome
Less common causes of NAFLD and NASH
Less common causes of NAFLD and NASH include
- disorders that cause your body to use or store fat improperly
- rapid weight loss
- certain infections, such as hepatitis C
- certain medicines, such as
- exposure to some toxins
A study funded by the National Institute of Diabetes and Digestive and Kidney Diseases found that people who had surgery to remove their gallbladder were more likely to develop NAFLD. More research is needed on the link between gallbladder removal and NAFLD.
How do doctors diagnose NAFLD and NASH?
Doctors use your medical history, a physical exam, and tests to diagnose nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH).
Your doctor will ask if you have a history of health conditions that make you more likely to develop NAFLD and NASH, such as
- overweight or obesity
- insulin resistance
- high levels of triglycerides or abnormal levels of cholesterol in your blood
- metabolic syndrome
- type 2 diabetes
Your doctor will ask about diet and lifestyle factors that may make you more likely to develop NAFLD and NASH, such as a lack of physical activity, eating a diet high in sugar and starch, or drinking sugary beverages.
Medical tests can’t show whether alcohol is the cause of fat in your liver. Your doctor will ask about your alcohol intake to find out whether fat in your liver is a sign of alcoholic liver disease or NAFLD.
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 NAFLD 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 jaundice, a condition that causes your skin and whites of your eyes to turn yellow
What tests do doctors use to diagnose NAFLD and NASH?
Doctors use blood tests, imaging tests, and sometimes liver biopsy to diagnose NAFLD and NASH.
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 or NASH if your blood test shows increased levels of the liver enzymes alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Your doctor may perform additional blood tests to find out if you have other health conditions that may increase your liver enzyme levels.
Your doctor may use the following imaging tests to help diagnose NAFLD:
- Ultrasound. Ultrasound uses a device called a transducer, which bounces safe, painless sound waves off your organs to create an image of their structure.
- Computerized tomography (CT) scans. CT scans use a combination of x-rays and computer technology to create images of your liver. For a CT scan, a health care professional may give you a solution to drink and an injection of a special dye, called contrast medium. Contrast medium makes the structures inside your body easier to see during the procedure. You’ll lie on a table that slides into a tunnel-shaped device that takes the x-rays.
- Magnetic resonance imaging (MRI). MRI machines use radio waves and magnets to produce detailed images of your organs and soft tissues without using x-rays. A health care professional may give you an injection of contrast medium. With most MRI machines, you’ll lie on a table that slides into a tunnel-shaped device. Some machines allow you to lie in a more open space; examining the liver can be more difficult with these machines.
A technician performs these tests in an outpatient center or a hospital. A technician can perform an ultrasound in a doctor’s office as well. A radiologist reads and reports on the images. You don’t need anesthesia, although you may receive light sedation during an MRI if you have a fear of confined spaces.
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 simple fatty liver or NASH. If you have cirrhosis, imaging tests may show nodules, or lumps, on your liver.
A doctor performs a liver biopsy at a hospital or an outpatient center. A health care professional will tell you how to prepare for a liver biopsy. You may need to stop taking certain medicines to prepare. You may be asked not to eat or drink anything for 8 hours before the procedure. During the procedure, you may receive a local anesthetic, sedatives, and pain medicine.
During the biopsy, you’ll lie on a table with your right hand resting above your head. The doctor will numb the area where he or she will insert the biopsy needle with a local anesthetic and then use the needle to take a small piece of liver tissue.
A liver biopsy is the only way to detect liver inflammation and damage to diagnose NASH. Doctors don’t recommend this test for everyone with NAFLD. Your doctor may recommend a liver biopsy if you are more likely to have NASH or if your other tests show signs of advanced liver disease or cirrhosis.
How do doctors treat NAFLD and NASH?
Doctors recommend weight loss to treat nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH). Weight loss can reduce fat in the liver; inflammation; and fibrosis, or scarring.
If you are overweight or obese, losing weight by making healthy food choices, limiting portion sizes, and being physically active can improve NAFLD and NASH. Losing at least 3 to 5 percent of your body weight can reduce fat in the liver. You may need to lose up to 10 percent of your body weight to reduce liver inflammation.7
Doctors recommend gradually losing 7 percent of your body weight or more over the course of 1 year.8 Rapid weight loss through fasting—eating and drinking nothing except water—can make NAFLD worse.
No medicines have been approved to treat NAFLD and NASH. However, researchers are studying medicines that may improve these conditions.
Some studies suggest that pioglitazone (Actos), a medicine for type 2 diabetes, improves NASH in people who don’t have diabetes. Researchers need more information to find out whether this medicine is safe and effective for long-term use in people with NASH.7
A study by the National Institute of Diabetes and Digestive and Kidney Diseases’ NASH Clinical Research Network found that treatment with vitamin E or pioglitazone improved NASH in about half of the people treated.9 Doctors may recommend vitamin E for people who have NASH and don’t have diabetes or cirrhosis.7 Talk with your doctor before taking vitamin E or pioglitazone.
For safety reasons, talk with your doctor before using dietary supplements, such as vitamins, or any complementary or alternative medicines or medical practices. Some herbal remedies can actually damage your liver.
How do doctors treat the complications of NASH?
If NASH leads to cirrhosis, doctors can treat the health problems caused by cirrhosis with medicines, operations, and other medical procedures. If cirrhosis leads to liver failure, you may need a liver transplant.
How can I prevent NAFLD and NASH?
Eating, Diet, & Nutrition
How can my diet help prevent or treat NAFLD and NASH?
If you don’t have nonalcoholic fatty liver disease (NAFLD) 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.
- saturated fats, found in meat, poultry skin, butter, lard, shortening, and all milk and dairy products except fat-free versions.
- trans fats, found in foods that list hydrogenated or partially hydrogenated oil on the label, such as crackers and snack foods, commercially baked goods such as cookies and cakes, and fried foods such as doughnuts and french fries.
- monounsaturated fats, found in olive, peanut, and canola oils.
- polyunsaturated fats, found in greatest amounts in corn, soybean, and safflower oils, and many types of nuts. Omega-3 fatty acids are a type of polyunsaturated fat. Sources include oily fish such as salmon, walnuts, and flaxseed oil.
Replacing saturated fats and trans fats in your diet with monounsaturated fats and polyunsaturated fats, especially omega-3 fatty acids, may reduce your chance of heart disease if you have NAFLD.
Your doctor may suggest other dietary changes to help treat NAFLD and NASH:
- Eat 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.
- Avoid 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.
- Avoid heavy alcohol use, which can damage your liver. For men, experts define heavy alcohol use as more than 4 drinks per day or more than 14 drinks per week. For women, heavy alcohol use is more than 3 drinks per day or more than 7 drinks per week.10
The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) and other components of the National Institutes of Health (NIH) conduct and support research into many diseases and conditions, including liver diseases.
What are clinical trials for NAFLD and NASH?
Clinical trials—and other types of clinical studies—are part of medical research and involve people like you. When you volunteer to take part in a clinical study, you help doctors and researchers learn more about disease and improve health care for people in the future.
Researchers are studying many aspects of nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH). For example, researchers are
- building databases of adults and children who have NAFLD
- comparing how people with and without NAFLD process and metabolize food
- studying how weight-loss surgery affects NAFLD in adolescents
Watch a video of NIDDK Director Dr. Griffin P. Rodgers explaining the importance of participating in clinical trials.
What clinical studies for NAFLD and NASH are looking for participants?
You can view a filtered list of clinical studies on NAFLD and NASH that are federally funded, open, and recruiting at www.ClinicalTrials.gov. You can expand or narrow the list to include clinical studies from industry, universities, and individuals; however, the NIH does not review these studies and cannot ensure they are safe. Always talk with your health care provider before you participate in a clinical study.
What have we learned about NAFLD and NASH from NIDDK-funded research?
The NIDDK has supported many research projects to learn more about NAFLD and NASH. For example, the NIDDK’s NASH Clinical Research Network (NASH CRN) has conducted studies to advance understanding of the causes, development, complications, and treatment of NASH in children and adults. NASH CRN studies include
- Pioglitazone or Vitamin E for NASH Study (PIVENS). Researchers found that a daily dose of the natural form of vitamin E—the type of vitamin E that comes from food sources and is not synthetic (laboratory-made)—improved NASH in study participants overall. Pioglitazone also improved some features of NASH, although researchers couldn’t prove that the improvements did not occur randomly. Many study participants taking pioglitazone gained weight, and many participants did not improve from either treatment. More research is needed to determine whether treatment with vitamin E or pioglitizone causes long-term risks.
- Treatment of Nonalcoholic Fatty Liver Disease in Children (TONIC) trial. The TONIC trial found that the natural form of vitamin E—the type of vitamin E that comes from food sources and is not synthetic (laboratory-made)—improved the most severe form of fatty liver disease in some children. More research is needed to determine whether treatment with vitamin E causes long-term risks.
- The Farnesoid X Receptor Ligand Obeticholic Acid in NASH Treatment Trial (FLINT). FLINT found that obeticholic acid (OCA) treatment was associated with improved liver function in people with NASH. OCA was also associated with increases in itching and total cholesterol. More research is needed to determine whether OCA is a safe and effective treatment for NASH and to fully understand how OCA affects cholesterol.
This content is provided as a service of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), part of the National Institutes of Health. The NIDDK translates and disseminates research findings to increase knowledge and understanding about health and disease among patients, health professionals, and the public. Content produced by the NIDDK is carefully reviewed by NIDDK scientists and other experts.
The NIDDK would like to thank:
Anna Mae Diehl, M.D., Duke University Medical Center, and Brent A. Tetri, M.D., Saint Louis University