This page was reviewed under our medical and editorial policy by
Maurie Markman, MD, President, Medicine & Science
This page was reviewed on January 5, 2022.
Non-alcoholic fatty liver disease (NAFLD) is a condition that develops when fat builds up inside the liver beyond the normal amount (about 5 percent to 10 percent of its weight). Over time, excess fat may harm the liver, which may be a risk factor for developing liver cancer. NAFLD is not the same as fatty liver disease that's caused by drinking too much alcohol.
About 24 percent of adults in the United States have NAFLD, according to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Both men and women are susceptible.
It mostly occurs in middle-aged or older people. However, because the obesity epidemic affects people of all ages, it’s starting to be seen in children, too. While no ethnic group is immune, it’s more common in people of Hispanic descent.
NAFLD is the umbrella term for two types of this condition.
NAFL, or non-alcoholic fatty liver: With NAFL, the liver is enlarged and could cause discomfort, but it’s less likely to be inflamed or have damage, and the patient is less likely to have complications.
NASH, or non-alcoholic steatohepatitis: This is the more severe form of NAFLD, with inflammation and damage as well as fat in the liver. The damage is seen as liver stiffness or scarring. In the advanced stage, this scarring is called cirrhosis. Cirrhosis can lead to liver failure, which requires a transplant. Up to 6.5 percent of Americans have this form of NAFLD, according to the NIDDK. It’s unclear why some people with NAFL progress to NASH and others don’t.
NASH may cause cirrhosis, and cirrhosis may cause liver cancer. Adults with cirrhosis are most at risk for hepatocellular carcinoma, the most common type of liver cancer. This form of liver cancer may start as small cancer nodules throughout the organ instead of as a single tumor.
The number of middle-aged obese men getting hepatocellular cancer is on the rise, and it has become a leading cause of death in this population.
A doctor may suspect a patient has fatty liver disease if his or her routine blood tests show increased levels of liver enzymes.
Sometimes, fat in the liver is seen on imaging tests—such as an X-ray, an ultrasound, a computed tomography (CT) scan or a magnetic resonance imaging (MRI) scan—of the abdomen. It’s also possible for a patient to have fat in the liver yet have normal enzyme levels.
Depending on the test results, the care team may order a FibroScan®, a type of ultrasound known as elastography. It uses sound waves to create images that measure the stiffness of liver tissue.
The patient may need to undergo a liver biopsy for a definitive diagnosis. During a biopsy, a needle is inserted into the liver through the patient's abdomen, and sample cells are drawn out. The cells are sent to a laboratory where a pathologist examines them under a microscope.
It’s not known what exactly causes some people to develop NAFLD, but it’s seen in patients who are obese, especially those with a large waist.
People are also at increased risk if they have any of the following:
Patients can have NAFLD and not know because it doesn’t always cause symptoms. When they do occur, the patient may experience some fatigue and pain on the right side of the upper abdomen, especially if the liver is enlarged.
As it progresses, the patient may have:
Signs and symptoms of cirrhosis include:
The exact chain of events that leads to NAFLD is unknown, but scientists have identified several factors that may play a role. For example, there may be a link between NAFLD and insulin resistance, which is when the body doesn’t respond well to insulin.
Research has shown that there also may be a link between developing NAFLD and consuming too much iron, cholesterol and refined sugars in processed foods.
Other studies have identified genetic changes that may make some people more likely to develop NAFLD. One is a variation in the gene PNPLA3, which provides instructions for making a protein found in fat and liver cells. The variation may cause an increase in production of PNPLA3, which in turn leads to a decrease in the breakdown of fats in the liver.
NAFLD may run in some families. Environmental and lifestyle factors, such as a lack of exercise and poor diet, may also factor into who develops this condition.
Because there are no Food and Drug Administration-approved medications for the treatment of NAFLD, one of the most helpful steps patients can take is to lose weight. The aim should be to do so at a slow and steady pace of 1 to 2 pounds a week—any more than that and NAFLD could get worse.
Be careful about the types of fats being consumed. Limit saturated fats such as red meat, butter and shortening, and avoid fried foods. Choose fat-free milk and other dairy products and foods with good-for-you fats, such as extra-virgin olive oil, flaxseed oil, and salmon and walnuts (both rich in omega-3 fatty acids). Other healthy foods include whole grains, fresh fruits and vegetables, and other high-fiber foods.
Work to manage chronic health conditions. For example, if the patient has diabetes, high cholesterol and/or high blood pressure, it's important to get them under control with diet and medications as needed.
Incorporate exercise into the patient's daily routine.
Take steps to protect the liver. That means no alcohol for patients who have NASH, abnormal liver enzymes, or hepatitis B or C. The care team may suggest no or limited amounts of alcohol for patients who have NAFL.
Tell the care team about over-the-counter medications. The patient should share details about any medications he or she currently takes (or wants to take), since some may not be healthy for the liver.
Long-term survival following an NAFLD diagnosis depends on a variety of factors, including the patient’s overall health, other conditions and age. One study found that patients with NAFLD lived 2.8 years less than those without the condition on average, with the strongest risk observed in those who were diagnosed between 40 and 60 years of age.
It’s important to speak with the care team to get a more accurate prognosis that’s tailored to the patient’s specific condition type and overall health.