Having a fatty liver means that fat has built up inside your liver cells beyond what’s normal. A healthy liver contains some fat, but when fat makes up more than about 5% of the liver’s weight, it’s classified as hepatic steatosis, or fatty liver disease. It’s extremely common, affecting roughly 30% of the global population, and most people who have it don’t know because it rarely causes symptoms in its early stages.
The condition was long known as nonalcoholic fatty liver disease (NAFLD), but in 2023 the medical community renamed it metabolic dysfunction-associated steatotic liver disease, or MASLD, to better reflect its connection to metabolic health rather than simply defining it by the absence of alcohol use. The more advanced inflammatory form, previously called NASH, is now called MASH.
How Fat Builds Up in the Liver
Your liver normally processes fats from your bloodstream, using some for energy and packaging the rest to send out to other tissues. Fatty liver develops when there’s an imbalance in this system: too much fat flowing in, too much new fat being created within the liver itself, or not enough fat being burned or exported. When the incoming fat overwhelms the liver’s ability to process it, the excess gets stored inside liver cells as fat droplets.
Obesity is the primary driver. Excess body fat leads to higher levels of fatty acids circulating in the blood, and the liver absorbs more of them than it can handle. But you don’t have to be significantly overweight to develop fatty liver. Insulin resistance, high blood sugar, high triglycerides, and high blood pressure all independently increase risk. Under the updated MASLD definition, a diagnosis requires hepatic steatosis plus at least one of these cardiometabolic risk factors.
Why Most People Don’t Notice Symptoms
Fatty liver in its early stages is largely silent. The liver has no pain receptors inside its tissue, so fat accumulation alone doesn’t typically hurt. When symptoms do appear, they tend to be 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 fatty liver is often discovered incidentally during blood work or imaging done for unrelated reasons.
How Fatty Liver Gets Diagnosed
Blood tests measuring liver enzymes are usually the first clue. Two enzymes, ALT and AST, are commonly checked. Normal levels for both fall between 0 and 35 units per liter. In early fatty liver, ALT tends to be higher than AST, producing an AST-to-ALT ratio below 0.8. As the disease progresses and scarring develops, that ratio climbs. A ratio above 1.0 raises concern for advanced scarring or other liver conditions.
However, liver enzymes can be completely normal even when significant fat is present. Imaging provides more direct evidence. Ultrasound is often the first step, and a specialized scan called FibroScan can measure both fat content and liver stiffness (a marker of scarring). A FibroScan fat measurement above 290 dB/m indicates advanced fat accumulation. In some cases, a liver biopsy is needed to determine exactly how much inflammation or scarring is present.
The Stages of Progression
Not all fatty liver is the same, and understanding where you fall on the spectrum matters enormously for your long-term outlook.
Simple steatosis is the earliest stage. Fat is present in the liver cells, but there’s no significant inflammation or damage. Most people with fatty liver stay at this stage, and it’s largely reversible.
MASH (steatohepatitis) develops when fat accumulation triggers inflammation and begins injuring liver cells. This is the turning point where real damage starts. MASH can lead to progressive scarring called fibrosis, graded from F1 (mild) through F4 (cirrhosis).
Cirrhosis represents the most advanced stage, where widespread scarring has replaced healthy liver tissue and the liver’s ability to function is compromised. At this point, liver transplant may eventually become necessary. Cirrhosis also increases the risk of liver cancer.
The Heart Disease Connection
Here’s something that surprises many people: the most dangerous consequence of fatty liver often isn’t liver failure. It’s heart disease. A large study comparing patients with fatty liver to matched controls found that cardiovascular events like heart attacks and strokes were 2.6 times more common in the fatty liver group, with 10.3% experiencing a cardiovascular event compared to 4.2% of controls. The risk of nonfatal events specifically was 3.7 times higher.
This makes sense given that fatty liver shares the same underlying metabolic drivers as heart disease: insulin resistance, chronic inflammation, and abnormal blood lipids. If you’re told you have fatty liver, it’s worth thinking of it as a signal that your cardiovascular risk is elevated too, not just a liver problem in isolation.
Who Is Most Affected
Fatty liver is not a rare condition. A meta-analysis covering 78 million participants across 38 countries estimated the global prevalence at 30.2%. Men are affected more often than women (36.6% versus 25.5%). Among adults with obesity, prevalence jumps to 57.5%. Children aren’t spared either: 14.3% of children overall and 38% of children with obesity show evidence of fatty liver.
Prevalence is remarkably consistent across regions. North America sits at about 29%, Europe at 30.2%, and Asia at 30.9%.
Reversing Fatty Liver With Weight Loss
The most effective treatment for fatty liver is weight loss, and the thresholds are well established. Losing 3 to 5% of your body weight is typically enough for fat to start disappearing from liver cells. For someone who weighs 200 pounds, that’s 6 to 10 pounds. To improve inflammation and scarring, a larger loss of about 10% of body weight is needed.
There’s no specific diet proven superior for fatty liver, but the principles are straightforward: reducing sugar and refined carbohydrate intake, limiting saturated fat, and increasing physical activity all help by addressing the insulin resistance that drives fat accumulation. Regular exercise improves liver fat even when weight on the scale doesn’t change dramatically, likely because it improves how your body handles insulin.
The First Approved Medication
For decades, there were no FDA-approved medications specifically for fatty liver disease. That changed in 2024 with the approval of resmetirom (brand name Rezdiffra), the first drug indicated for adults with MASH who have moderate to advanced liver scarring (stages F2 to F3) but have not yet progressed to cirrhosis. The drug works by activating a thyroid hormone receptor concentrated in the liver, which helps the liver burn off stored fat. It’s prescribed alongside diet and exercise, not as a replacement for them.
Resmetirom represents a significant milestone, but it’s targeted at people who already have substantial scarring. For the majority of people with simple fatty liver or mild disease, lifestyle changes remain the cornerstone of management.