Metabolic Dysfunction-Associated SteatohepatitisMASH, formerly called nonalcoholic steatohepatitis (NASH)

MASH is the form of fatty liver disease in which fat buildup also causes inflammation and liver cell damage. In simple fatty liver, called MASL, the liver holds extra fat but has little or no inflammation or damage. MASH is more serious because the inflammation can lead to scarring (fibrosis), and scarring can progress to cirrhosis. MASH was formerly called nonalcoholic steatohepatitis (NASH), and fatty liver disease was formerly called NAFLD. It is not caused by heavy alcohol use. Experts are not sure why some people with fatty liver develop MASH and others do not.

Yes, in many cases, if it is caught before permanent scarring. With the right lifestyle and diet changes, a person can stop or slow the progression of MASH. Gradual weight loss, regular exercise, a liver-healthy diet, less alcohol, and lower cholesterol are the building blocks. Once scarring reaches cirrhosis, the damage may be irreversible, and treatment then focuses on protecting the liver and managing complications. This is why early testing matters, even when you feel fine.

Many people with MASH have no symptoms for years, so it is often called a silent disease. When symptoms appear, the most common first signs are tiredness and an ache or pain in the upper right side of the belly. Other symptoms include loss of appetite, weakness, itchy skin, weight loss, and swelling in the belly or legs. Signs of more advanced disease include yellow skin and eyes (jaundice), web-like clusters of blood vessels under the skin, nosebleeds, breast enlargement in men, and confusion. Talk with your doctor promptly if you notice any of these.

Doctors use several steps because MASH rarely causes symptoms. They start with your medical history, including medical conditions, medications, alcohol use, and diet, followed by a physical exam and blood tests. Imaging such as an ultrasound, CT scan, or MRI can show fat in the liver. A FibroScan is a painless test that measures liver stiffness and fat in about 10 to 15 minutes, and results are grouped into fibrosis stages F0 to F4, where F4 is cirrhosis. A liver biopsy, which examines a small tissue sample under a microscope, is the most precise way to confirm MASH and the exact stage of scarring.

Lifestyle change is the first step. Losing 3 to 5% of body weight can reduce liver fat, and losing more than 10% is often needed to improve inflammation and scarring. Doctors also recommend at least 150 minutes of aerobic exercise a week, strength training two or three days a week, and a liver-healthy diet. Rezdiffra (resmetirom) is an oral medicine approved in March 2024 for adults with MASH and moderate to advanced scarring (F2 to F3) but not cirrhosis, used together with diet and exercise. In selected people, doctors may also consider vitamin E or bariatric surgery. Your care team decides which options fit you.

Fatty liver disease is one of the most common causes of liver disease in the United States. Experts estimate that about 24% of U.S. adults have it, but only a small share of them have MASH. Current estimates suggest about 1.5% to 6.5% of U.S. adults have MASH. Because it often causes no symptoms, many people do not know they have it. If you have obesity, type 2 diabetes, high cholesterol, or high blood pressure, ask your doctor about liver testing.

Yes. Without treatment, the inflammation in MASH can cause fibrosis, and fibrosis can progress to cirrhosis, where the liver is scarred and permanently damaged. Cirrhosis can lead to liver failure and liver cancer, and some people need a liver transplant evaluation. The metabolic conditions behind fatty liver disease can also raise the risk of heart disease and diabetes. Treating MASH early and managing weight, blood sugar, cholesterol, and blood pressure lowers the chance of these complications.