Metabolic dysfunction-associated steatotic liver disease, or MASLD, happens when too much fat builds up in the liver, and it’s becoming more common worldwide. This condition used to be called nonalcoholic fatty liver disease, but the name was changed to better reflect what actually causes it—problems with how the body handles food, energy, and metabolism.

What is MASLD and How Common is It?

Metabolic dysfunction-associated steatotic liver disease is a group of liver conditions that develop when your body stores large amounts of fat in your liver. When fat makes up more than five to ten percent of your liver’s total weight, you have this condition. The liver normally contains some fat, but when it accumulates in larger amounts, it can lead to inflammation and damage over time.^[1]

MASLD is now one of the most common forms of chronic liver disease (long-lasting liver problems). The condition affects roughly one in three adults globally, with experts estimating that more than 30 percent of people worldwide have MASLD. In Australia alone, about one in three adults has been found to have this condition.^[1][19]

The name change from nonalcoholic fatty liver disease to MASLD reflects a better understanding of what causes this condition. The new name emphasizes that metabolic problems—issues with how your body processes food into energy and manages blood sugar and fats—are at the root of the disease. This is different from liver damage caused by alcohol consumption.^[4]

MASLD can affect people of all ages. While it’s most commonly diagnosed in people between 50 and 60 years old, it’s increasingly appearing in younger people, including adolescents and children. This rise is closely tied to the growing number of people with obesity and diabetes around the world.^[4][7]

What Causes Metabolic Dysfunction-Associated Steatotic Liver Disease?

MASLD develops when you have what doctors call metabolic dysfunction. This refers to a group of conditions that affect how your body turns food into energy and manages important substances like blood sugar and fats in your blood. When these processes don’t work properly, fat begins to accumulate in your liver cells.^[1]

The condition is closely linked to several metabolic problems. Dyslipidemia—having high levels of fatty substances in your blood, including cholesterol—is one key factor. Another is insulin resistance, which happens when cells in your muscles, fat tissue, and liver don’t respond normally to insulin, a hormone that helps control blood sugar levels. When cells become resistant to insulin, your body has trouble managing blood sugar properly.^[1]

Having obesity (when your body mass index is 30 or higher) is a major cause of MASLD. People who carry extra weight around their belly are at particularly high risk. Type 2 diabetes, a condition where blood sugar levels stay too high for extended periods, also commonly leads to fat buildup in the liver.^[1]

The exact way MASLD develops isn’t completely understood, but scientists believe insulin resistance plays a central role. When your body can’t use insulin effectively, it triggers a cascade of problems that lead to fat accumulation in liver cells. Researchers have also identified several genetic variations that can increase a person’s risk of developing MASLD, suggesting that some people may be more prone to the condition because of their genetic makeup.^[1][4]

Who is at Risk?

Certain groups of people are more likely to develop MASLD than others. Understanding these risk factors can help people recognize if they need to take preventive steps or get screened for the condition.

People with overweight or obesity face the highest risk of developing MASLD. The risk becomes even greater for those with type 2 diabetes. Having both obesity and diabetes creates a particularly strong likelihood of developing fatty liver disease.^[17]

Age matters when it comes to MASLD risk. Being 40 years old or older increases your chances of developing the condition. However, this doesn’t mean younger people are safe—children and adolescents with obesity can also develop MASLD.^[17]

Several other health conditions and lifestyle factors raise your risk. High blood pressure and high cholesterol levels are both connected to MASLD. People who don’t move around much—those with sedentary (inactive) lifestyles—are more vulnerable. Smoking cigarettes also increases risk.^[17]

Your diet plays an important role too. Eating a diet high in sugar and saturated fats can contribute to fat buildup in the liver. This is one reason why MASLD rates have increased, as processed foods containing these ingredients have become more common in many people’s diets.^[17]

Interestingly, some people develop MASLD even when they don’t have any of the typical risk factors. This has led scientists to investigate whether genetic factors might make certain people more susceptible to the condition, regardless of their lifestyle or other health conditions.^[17]

Symptoms: What Does MASLD Feel Like?

One of the most challenging aspects of MASLD is that many people don’t feel sick at all, especially in the early stages. The condition can develop silently over several years without causing any noticeable symptoms. This is why MASLD is often discovered accidentally during medical tests performed for completely different reasons.^[1]

When MASLD progresses to a more serious form called MASH (metabolic dysfunction-associated steatohepatitis), symptoms may start to appear. MASH occurs when the fat buildup in your liver causes inflammation and damage to liver cells. At this stage, some people experience an ache or discomfort in the upper right part of their abdomen, where the liver sits.^[1]

Extreme tiredness and weakness are common symptoms for people with more advanced MASLD or MASH. This fatigue isn’t the normal tiredness you feel at the end of a busy day—it’s a profound exhaustion that doesn’t improve much with rest. People may also notice they’ve lost their appetite and are eating less than usual, which can lead to unexpected weight loss.^[1]

As liver damage becomes more severe, other symptoms can develop. A swollen belly may occur as fluid builds up in the abdomen. The skin and the whites of the eyes may turn yellow, a condition called jaundice or scleral icterus. This yellowing happens because the damaged liver can’t properly process certain substances in the blood.^[1]

If MASH advances further, additional symptoms may appear, including itchy skin, swelling in the legs or feet, trouble breathing, and easy bruising or bleeding. Some people notice unusual spider-like blood vessels appearing beneath their skin.^[17]

Can MASLD Be Prevented?

The good news about MASLD is that it can often be prevented through healthy lifestyle choices. Because the condition is so closely tied to obesity, diabetes, high cholesterol, and other metabolic problems, preventing these conditions also helps prevent MASLD.^[1]

Maintaining a healthy body weight is one of the most important preventive steps. For people who already have excess weight, even modest weight loss can make a significant difference. Losing seven to ten percent of your total body weight has been shown to reduce liver fat and improve symptoms. This might sound like a lot, but for someone who weighs 200 pounds, it means losing just 14 to 20 pounds.^[13]

Regular physical activity helps prevent MASLD in multiple ways. Exercise helps control body weight, improves how your body uses insulin, and can directly reduce fat in the liver. Experts recommend getting at least 150 to 240 minutes of moderate to vigorous aerobic exercise each week. This could include activities like brisk walking, swimming, cycling, or dancing—anything that gets your heart rate up.^[18]

Eating a healthy, balanced diet is crucial for preventing MASLD. The Mediterranean diet has strong evidence supporting its benefits for liver health. This way of eating emphasizes lots of vegetables, fruits, whole grains, legumes (beans and lentils), olive oil, and nuts. It includes moderate amounts of fish, seafood, eggs, cheese, and yogurt, while limiting red meat, processed meats like sausages and ham, and sweets.^[19]

Reducing your intake of processed foods and added sugars is particularly important. This includes limiting foods high in fructose, a type of sugar found not only in table sugar but also in many processed foods and sweetened drinks. While fruit contains fructose, it also provides important vitamins and fiber, so eating moderate amounts (up to two pieces per day) is considered healthy.^[19]

Managing other health conditions also helps prevent MASLD. Keeping blood pressure, blood sugar, and cholesterol levels in healthy ranges reduces the risk of developing fatty liver disease. If you have diabetes or pre-diabetes, working with your healthcare provider to manage these conditions is essential.^[17]

Avoiding smoking and limiting alcohol consumption are also important. While MASLD isn’t caused by alcohol, drinking can still contribute to liver problems and should be limited or avoided, especially if you already have risk factors for liver disease.^[17]

How MASLD Changes Normal Liver Function

To understand how MASLD affects your body, it helps to know what a healthy liver normally does. Your liver is one of your body’s largest and most important organs, performing hundreds of essential tasks. It processes nutrients from the food you eat, filters toxins and waste products from your blood, produces proteins needed for blood clotting, and stores vitamins and energy in the form of glycogen.^[3]

When MASLD develops, fat droplets begin accumulating inside liver cells. At first, this may not interfere much with liver function. However, as more fat builds up, it can trigger inflammation. The liver becomes stressed trying to deal with the excess fat, and this stress can damage liver cells.^[4]

When inflammation occurs along with fat accumulation, the condition progresses from simple MASLD to MASH. In MASH, damaged liver cells release signals that activate the liver’s repair system. Unfortunately, this repair process doesn’t always work perfectly. Instead of fully restoring healthy liver tissue, the liver may form scar tissue—a process called fibrosis.^[1]

Fibrosis creates bands of tough, inflexible tissue within the liver. Initially, small amounts of scar tissue may not cause serious problems. However, if the damage continues and more scar tissue forms, it can progress to cirrhosis—extensive scarring that seriously disrupts liver function. In cirrhosis, the normal liver structure is replaced by hard, scarred tissue that can’t perform the liver’s normal jobs effectively.^[5]

Cirrhosis can lead to multiple serious complications. Scar tissue can block blood flow through the liver, causing blood to back up and potentially rupture blood vessels. The damaged liver may struggle to filter toxins from the blood, leading to buildup of harmful substances. It may also fail to produce enough important proteins, resulting in problems with blood clotting and fluid balance.^[10]

In some cases, MASH and cirrhosis can lead to hepatocellular carcinoma, a type of liver cancer. The chronic inflammation and cell damage increase the risk that liver cells will begin growing abnormally and form tumors. In severe cases, the liver may fail completely, meaning it can no longer perform its essential functions—a life-threatening situation that may require a liver transplant.^[1]

MASLD doesn’t just affect the liver. Research shows the condition increases the risk of cardiovascular disease—problems with the heart and blood vessels. In fact, cardiovascular disease is the leading cause of death in people with fatty liver disease. MASLD may also raise the risk of kidney disease and certain types of cancer, including breast cancer and colorectal cancer.^[1][19]

Understanding Stages of MASLD

MASLD exists on a spectrum, ranging from mild fat accumulation to severe liver damage. Understanding these stages helps patients and doctors know how serious the condition is and what treatment approaches might work best.

The earliest and mildest form is simple hepatic steatosis, which just means fat in the liver. At this stage, there’s fat buildup but minimal inflammation or cell damage. Many people stay at this stage for years without the condition getting worse, especially if they maintain healthy habits.^[5]

MASH represents a more serious stage where inflammation and liver cell damage occur along with fat accumulation. Not everyone with MASLD develops MASH, but those who do face higher risks of progression to more severe disease. Experts estimate that about 13 percent of people with MASLD also have MASH.^[17]

The presence of fibrosis (scarring) indicates that liver damage has been occurring over time. Fibrosis is staged from mild (stage 1 or 2) to severe (stage 3 or 4). Advanced fibrosis means extensive scarring has developed, increasing the risk of progression to cirrhosis. Doctors use various scoring systems to measure how much fibrosis is present.^[4]

Cirrhosis represents the most advanced stage of liver scarring. At this point, widespread scar tissue has replaced normal liver tissue, significantly impairing liver function. Cirrhosis can lead to liver failure and the need for liver transplantation in severe cases.^[5]

One encouraging aspect of MASLD is that the early stages can be reversible. Research shows that adopting a healthy diet, increasing physical activity, and losing weight can reduce liver fat and even reverse MASLD in some cases. However, once significant scarring develops, it becomes much more difficult to reverse the damage, though further progression may be slowed or stopped.^[3]