Steatosis of the liver is the medical term for fatty liver, a condition where fat builds up inside liver cells. It affects roughly 30% of adults worldwide, making it one of the most common liver conditions on the planet. Most people with steatosis have no symptoms and discover it incidentally during imaging for something else.
How Fat Builds Up in the Liver
Your liver normally contains small amounts of fat. Steatosis develops when the balance between fat coming in and fat going out tips in the wrong direction. The liver acquires fat two ways: by pulling fatty acids from your bloodstream and by manufacturing new fat from sugars you eat (a process called de novo lipogenesis). It removes fat by burning fatty acids for energy or packaging them into particles that get shipped out into the blood.
When more fat arrives or gets made than the liver can burn or export, the excess accumulates as triglyceride droplets inside liver cells. About 60% of the fat that builds up comes from fatty acids already circulating in the blood, often released from body fat stores. Another 26% is newly manufactured from dietary sugars. The remainder comes directly from dietary fat. This means steatosis isn’t just about eating fatty foods. Excess sugar and carbohydrate intake, insulin resistance, and the overall size of your body’s fat stores all play major roles.
Updated Terminology
If you’ve seen terms like NAFLD, MASLD, NASH, and MASH used interchangeably, here’s the short version: in 2023, an international consensus renamed nonalcoholic fatty liver disease (NAFLD) to metabolic dysfunction-associated steatotic liver disease (MASLD). The old term defined the condition by what it wasn’t (not caused by alcohol), while the new name connects it to its actual driver: metabolic dysfunction. Similarly, the more advanced inflammatory form, previously called NASH (nonalcoholic steatohepatitis), is now called MASH (metabolic dysfunction-associated steatohepatitis).
Under the updated criteria, a diagnosis of MASLD requires both fat in the liver and at least one cardiometabolic risk factor, such as obesity, type 2 diabetes, high blood pressure, or elevated blood sugar. You may still see “NAFLD” in older lab reports or articles, but it refers to the same condition.
Who Gets It and Why
The strongest risk factors are carrying excess weight (particularly around the midsection), having type 2 diabetes, and meeting criteria for metabolic syndrome. Specific markers that raise risk include a waist circumference above 102 cm (40 inches) in men or 88 cm (35 inches) in women, blood pressure at or above 130/85, and fasting blood sugar in the prediabetic range. About 36% of people diagnosed with fatty liver disease also have high blood pressure.
That said, steatosis isn’t exclusive to people with obesity. Lean individuals can develop it too if they have metabolic irregularities like insulin resistance or elevated triglycerides. Genetics, certain medications, rapid weight loss, and a diet high in refined carbohydrates and sugary drinks also contribute. Latin America has the highest regional prevalence globally.
Symptoms and How It’s Found
Most people with simple steatosis feel nothing. When symptoms do appear, they’re vague: fatigue, a general sense of not feeling well, or mild discomfort in the upper right side of the abdomen. These are easy to attribute to other causes, which is why steatosis often goes undetected for years.
The most common way steatosis is identified is through an abdominal ultrasound, where the liver appears brighter than normal. A more precise tool is a FibroScan, which measures liver fat using a score called the controlled attenuation parameter (CAP). Scores below about 263 dB/m suggest little to no excess fat, while scores above 288 dB/m indicate moderate steatosis and scores above 330 dB/m point to severe fat accumulation. MRI can measure liver fat content even more accurately but is used less often due to cost.
When Steatosis Gets Worse
Simple steatosis on its own is considered the earliest and most reversible stage. The liver has excess fat but no significant inflammation or scarring. For many people, it stays that way indefinitely. But 20% to 30% of people with fatty liver disease progress to MASH, where inflammation begins damaging liver cells.
Once inflammation sets in, the liver can develop fibrosis (scarring). This progression is typically slow. In people with simple steatosis, fibrosis advances roughly one stage every 14 years on average. In those with MASH, that timeline compresses to about every 7 years. Over years to decades, severe fibrosis can lead to cirrhosis or, in some cases, liver cancer. The key point is that simple steatosis and MASH are not the same condition, and the majority of people with fatty liver never reach advanced scarring.
Reversing Liver Fat Through Weight Loss
Weight loss is the most effective treatment for steatosis, and the thresholds are well established. Losing just 5% of your body weight reduces liver fat by about 25%, as measured by MRI. That’s 10 pounds for someone who weighs 200. Losing 7% to 10% of body weight can improve not only fat content but also inflammation and early-stage fibrosis. These benefits have been demonstrated consistently across multiple studies, and they hold regardless of which specific diet a person follows, as long as the weight comes off and stays off.
Exercise helps independently of weight loss, though its effects are strongest when combined with dietary changes. Both aerobic exercise and resistance training have shown benefits for reducing liver fat.
Dietary Patterns That Help
The Mediterranean dietary pattern has the strongest evidence for reducing liver fat. It emphasizes olive oil, fish, vegetables, legumes, whole grains, and nuts while limiting red meat, processed foods, and added sugars. In clinical trials, this pattern reduced liver fat by 38% over six weeks in one study, independent of weight loss or changes in waist size. Other trials found that it lowered liver enzyme levels (a marker of liver stress) more effectively than standard low-fat diets, even when total calorie intake was the same.
The specific components that seem to matter most are replacing saturated fats with monounsaturated fats (like olive oil), maintaining a healthy ratio of omega-3 to omega-6 fats, eating plenty of fiber, and cutting back on fructose and refined carbohydrates. Sugary beverages are a particularly significant source of the fructose that fuels new fat production in the liver.
Medication Options
For decades, no medication was approved specifically for fatty liver disease. That changed in March 2024 when the FDA approved resmetirom (brand name Rezdiffra), the first drug indicated for adults with MASH and moderate to advanced liver scarring. It works by activating a thyroid hormone receptor in the liver that helps reduce fat accumulation. It’s approved for use alongside diet and exercise, not as a replacement for lifestyle changes, and it’s intended for people who already have significant fibrosis rather than simple steatosis.
Resmetirom was approved under the FDA’s accelerated pathway, meaning long-term outcomes are still being confirmed. For the vast majority of people with early-stage steatosis and no significant scarring, lifestyle changes remain the primary approach.