Metabolic dysfunction-associated steatohepatitis (MASH) is a serious liver condition that develops when excess fat in the liver triggers inflammation and cell damage, potentially leading to severe complications like cirrhosis and liver cancer if left untreated.

Understanding this condition is crucial because it often progresses silently over many years without obvious symptoms. Previously known as nonalcoholic steatohepatitis or NASH, MASH represents a more severe stage of fatty liver disease that requires attention and intervention. The condition affects millions of people worldwide, yet many remain unaware they have it until significant liver damage has occurred.

How Common Is MASH Around the World

MASH is part of a broader spectrum of liver diseases called MASLD, which stands for metabolic dysfunction-associated steatotic liver disease. This larger group affects an enormous number of people globally. Experts estimate that more than 30% of people worldwide have some form of MASLD, which translates to roughly one in every three adults^[2]. In the United States alone, approximately 100 million people have been diagnosed with fatty liver disease conditions^[16].

Within this large population of people with fatty liver disease, about 20% to 25% will develop the more serious form called MASH^[1][16]. This means that roughly 13% of people with MASLD progress to having inflammation and liver damage, not just fat accumulation^[16]. The condition is becoming increasingly common, especially in Western and Middle Eastern countries, largely due to rising rates of obesity and type 2 diabetes^[5].

MASH has become the leading reason for liver transplants among women and people over 65 years old in the United States. Medical experts predict it will soon become the number one reason for liver transplantation overall^[19]. The disease affects people of all ages, races, and ethnicities, including children. However, certain groups face higher risks based on their metabolic health conditions.

What Causes This Liver Disease

MASH develops when too much fat builds up in the liver and triggers an inflammatory response. The liver is one of your body’s most important organs, weighing about three pounds and sitting in the upper-right side of your abdomen below your ribs. It performs vital functions like converting food into energy, helping your body process medications, removing toxins from your blood, and producing bile to aid digestion^[23].

When excess fat accumulates in liver cells, it creates stress on the organ. In some people, this fat buildup causes the liver to become inflamed and damaged. The condition is closely linked to problems with how your body processes sugar and fat^[1]. This happens through a complex process involving insulin resistance, which occurs when cells in your muscles, fat, and liver don’t respond properly to insulin, a hormone that manages blood sugar levels^[2].

Unlike liver disease caused by heavy alcohol consumption, MASH occurs in people who drink little or no alcohol. The name emphasizes that metabolic dysfunction—not alcohol—is the primary driver of the disease^[4][8]. Researchers continue to study why some people with fatty liver develop simple fat accumulation while others progress to the more severe inflammatory form. Genetic variations appear to play a role in increasing risk for some individuals^[2].

Risk Factors That Increase Your Chances

Several health conditions and characteristics significantly increase the likelihood of developing MASH. Understanding these risk factors helps identify who should be screened and monitored more carefully.

Obesity or being overweight represents one of the strongest risk factors. People with a body mass index (BMI) of 30 or higher have significantly increased risk. Those who carry extra weight around their belly face even greater danger^[2]. Type 2 diabetes is another major risk factor closely tied to MASH development^[1][7].

High cholesterol levels and elevated triglycerides, which are types of fat in your blood, increase the likelihood of developing MASH. High blood pressure also contributes to risk^[1]. These conditions often cluster together in what doctors call metabolic syndrome. Having insulin resistance, even without full diabetes, creates vulnerability to liver fat accumulation and inflammation^[2].

Age plays a role, with people over 40 facing higher risk. Smoking increases the chances of developing MASH. A diet high in sugar and saturated fat, combined with physical inactivity, creates an environment where the disease can develop^[16]. Interestingly, some people develop MASH despite not having obesity or being overweight, particularly if they have metabolic issues like high cholesterol or high blood pressure^[1].

Recognizing the Symptoms

MASH is often called a “silent disease” because it typically produces few or no symptoms during its early stages^[19]. The condition develops slowly over many years, and you may not notice any changes in how you feel until significant liver damage has occurred^[1]. This silent nature makes the disease particularly dangerous, as people can live with progressive liver damage without realizing anything is wrong.

When symptoms do appear, they tend to be non-specific, meaning they could be attributed to many different health issues. This makes MASH easy to overlook or misdiagnose. The most common early symptom is fatigue—feeling unusually tired or lacking energy for daily activities^[1][19]. Many people also experience discomfort or pain in the upper right side of the belly, where the liver is located^[1].

As the disease progresses and causes more severe liver damage, additional symptoms may develop. These include unexplained weight loss, muscle weakness or loss of muscle mass, and swelling in the belly or legs^[1]. More advanced cases may cause a yellowish tint to the skin and eyes, a condition called jaundice, which occurs when the liver can no longer process waste products properly^[1][2].

Because early MASH rarely causes obvious symptoms, regular checkups become critically important, especially if you have risk factors like obesity, diabetes, or high cholesterol^[1]. Healthcare providers can detect the disease through blood tests and imaging studies before you feel sick, allowing for earlier intervention when treatment is most effective.

Prevention Strategies

Preventing MASH centers on managing the metabolic conditions that contribute to its development. Since the disease is closely linked to obesity, diabetes, and other metabolic issues, addressing these factors can significantly reduce your risk or prevent existing fatty liver disease from progressing to the inflammatory stage.

Maintaining a healthy weight is one of the most effective prevention strategies. For people who are overweight or have obesity, losing even a modest amount of weight can make a substantial difference. Research shows that losing 7% to 10% of total body weight can reduce liver inflammation and scarring^[14]. Weight loss helps decrease the amount of fat in the liver and reduces the stress that leads to inflammation.

Adopting a well-balanced, nutritious diet plays a crucial role in prevention. While specific dietary approaches will vary, focusing on whole foods, vegetables, fruits, lean proteins, and healthy fats supports liver health. Reducing consumption of foods high in sugar and saturated fat helps prevent fat accumulation in the liver^[16][17]. The Mediterranean diet pattern has shown particular promise for liver health in research studies^[17].

Regular physical activity serves as another powerful prevention tool. Staying active helps your body process sugar and fat more effectively, reducing the likelihood of developing insulin resistance. Exercise benefits liver health even without significant weight loss^[17]. Current evidence supports engaging in moderate-to-vigorous aerobic exercise for 150 to 240 minutes per week for optimal liver protection^[17].

Managing existing health conditions like diabetes, high blood pressure, and high cholesterol helps prevent MASH development. Working with healthcare providers to control these conditions through lifestyle changes and, when necessary, medications reduces metabolic stress on the liver. Avoiding or quitting smoking also lowers risk^[16].

For people with metabolic risk factors or a family history of liver disease, regular screening becomes an important preventive measure. Early detection allows for intervention before significant damage occurs^[16][19].

How the Disease Changes Normal Body Functions

Understanding what happens inside the body when MASH develops helps explain why the condition can become so serious. The disease process involves multiple changes to normal liver structure and function.

The liver normally contains very little fat. When more than 5% of the liver’s weight consists of fat, a person has developed steatotic liver disease^[16]. This fat accumulation doesn’t happen overnight but builds up gradually as the body struggles with metabolic dysfunction. Insulin resistance plays a central role in this process. When cells don’t respond properly to insulin, the body compensates by producing more insulin. This excess insulin triggers increased fat production and storage in liver cells^[6].

In simple fatty liver, this fat buildup causes minimal inflammation or cell damage. However, in MASH, the accumulated fat creates significant stress on liver cells. This stress triggers an inflammatory response as the body’s immune system attempts to address the problem. The inflammation causes liver cells to swell, a process called ballooning^[19]. These swollen, damaged cells cannot perform their normal functions effectively.

As inflammation continues over time, the liver attempts to repair itself by forming scar tissue, a process called fibrosis^[1]. Initially, small bands of scar tissue develop. If the inflammatory process continues, more extensive scarring occurs. This progressive scarring can eventually lead to cirrhosis, where severe scarring throughout the liver significantly impairs its ability to function^[1].

The scarring disrupts normal blood flow through the liver, making it harder for the organ to filter toxins from the blood, produce essential proteins, and perform its hundreds of other vital functions^[19]. In advanced stages, the damaged liver may not be able to regenerate healthy tissue, and the scarring becomes permanent. This can progress to liver failure, where the liver can no longer sustain life without a transplant^[1].

MASH also increases the risk of developing hepatocellular carcinoma, the most common type of liver cancer^[1][19]. The chronic inflammation and cellular damage create an environment where abnormal cells can multiply uncontrollably. Beyond liver-specific effects, MASH significantly increases the risk of cardiovascular disease, including heart attacks and strokes, making it a systemic health concern^[1][19].

The relationship between MASH and other metabolic diseases creates a complex web of health challenges. MASLD is now considered the liver manifestation of metabolic syndrome, meaning fatty liver disease is intrinsically connected to conditions like diabetes, obesity, and cardiovascular disease^[19]. This interconnection explains why people with MASH often have multiple health concerns requiring comprehensive management.