Fatty liver disease is extraordinarily common. An estimated 1.3 billion people worldwide were living with it in 2023, roughly 16% of the global population. In the United States, it ranks as the most common chronic liver condition, and its prevalence has been climbing steadily alongside rising rates of obesity and type 2 diabetes.
Who Gets Fatty Liver Disease
The overall numbers are striking, but the risk isn’t spread evenly. Your likelihood of having fatty liver depends heavily on a few key factors, especially your weight and metabolic health. Up to 50% of people with obesity have fatty liver, and that figure climbs to 90% among those with severe (class III) obesity. Among people with type 2 diabetes, prevalence reaches roughly 70%, with about half of those having a more aggressive form that involves active liver inflammation.
Age and sex also matter. Men tend to develop fatty liver earlier in life, while women see their risk increase after menopause. Among adolescents, the global prevalence is about 4.7%, with boys affected at nearly twice the rate of girls (5.8% vs. 3.5%). These numbers in young people are especially concerning because they suggest decades of potential liver damage ahead.
Ethnicity plays a role as well, though more in how the disease behaves than in whether you get it. Hispanic individuals tend to have higher rates and more severe liver inflammation. Black individuals, when they do develop fatty liver, generally show milder liver scarring and less inflammation compared to both white and Hispanic patients.
Fatty Liver in People at a Healthy Weight
One of the most important things to understand about fatty liver is that you don’t need to be overweight to have it. About 5 to 13% of the global population has what’s called “lean” fatty liver, meaning their BMI falls in the normal range but they still have excess fat in the liver along with at least one metabolic risk factor like high blood sugar, elevated triglycerides, or high blood pressure. Among everyone diagnosed with fatty liver, nearly one in five is lean.
This form is especially common in Asian countries, where prevalence runs around 12 to 15% compared to about 9% in Western countries. The reasons likely involve differences in body composition: some people store a disproportionate amount of fat around their internal organs rather than under the skin, so their weight looks normal on a scale while their liver tells a different story.
What “Fatty Liver” Actually Means Now
If you’ve seen both the terms NAFLD and MASLD floating around, here’s the short version: they describe essentially the same condition, but the medical world officially renamed it in 2023. The old name, nonalcoholic fatty liver disease (NAFLD), was defined by what it wasn’t (not caused by alcohol). The new name, metabolic dysfunction-associated steatotic liver disease (MASLD), defines it by what it is: liver fat driven by metabolic problems.
To qualify for a MASLD diagnosis, you need fat in the liver plus at least one of the following: a BMI of 25 or higher (23 in Asian populations), fasting blood sugar of 100 mg/dL or above, blood pressure at or above 130/85, triglycerides at or above 150 mg/dL, or low HDL cholesterol. Since these metabolic markers are so common in industrialized populations, the vast majority of people who had NAFLD under the old definition also meet MASLD criteria under the new one.
Why the Numbers Keep Climbing
Fatty liver prevalence has been rising for decades, and the trajectory isn’t flattening. The 2023 estimate of 1.3 billion affected people globally is projected to keep growing as obesity rates increase in low- and middle-income countries that are adopting more processed, calorie-dense diets. In the U.S., where roughly 42% of adults have obesity, fatty liver has become so widespread that many people have it without knowing. Most cases produce no symptoms until the disease has advanced significantly.
The financial toll reflects the scale of the problem. Annual healthcare costs for fatty liver in the U.S. total approximately $15.7 billion. For an individual without complications, average yearly costs run about $28,000. But if the disease progresses to cirrhosis, those costs jump to over $110,000 per year, and patients who need a liver transplant can face bills exceeding $300,000 annually.
The Spectrum From Mild to Serious
Not everyone with fatty liver will develop serious problems, and that’s a crucial distinction. The disease exists on a spectrum. At one end, simple fat accumulation in the liver is relatively benign. Many people live with this for years without progressing. At the other end, about 35% of people with type 2 diabetes and fatty liver have the inflammatory form (previously called NASH, now called MASH), where the immune system actively damages liver cells. This inflammation can lead to scarring, and roughly one in five people with diabetes and fatty liver already has significant scarring.
About 7% of people with diabetes and fatty liver progress all the way to cirrhosis, where the scarring is severe enough to impair liver function. Cirrhosis also raises the risk of liver cancer. Doctors can estimate your risk of advanced scarring using a simple blood-based calculation called the FIB-4 score, which combines your age, platelet count, and two liver enzymes. A score below 1.45 reliably rules out significant scarring in about 90% of cases, while a score above 2.67 identifies high-risk patients with about 80% accuracy.
What Drives the Disease
Fatty liver develops when the liver takes in more fat than it can process and export. Insulin resistance is the central driver for most people. When your cells respond poorly to insulin, your body compensates by producing more of it, which promotes fat storage in the liver. This is why the condition clusters so tightly with type 2 diabetes, obesity, and metabolic syndrome.
But the metabolic picture is only part of the story. Genetics influence how your liver handles fat, which helps explain why some lean people develop the disease while some people with obesity never do. Diet quality matters independently of weight: diets high in added sugars, particularly fructose, and refined carbohydrates promote liver fat accumulation even when total calorie intake isn’t excessive. Physical inactivity compounds the problem by reducing the muscles’ ability to burn fat and respond to insulin.
The good news embedded in these numbers is that fatty liver, especially in its earlier stages, responds well to lifestyle changes. Losing 5 to 10% of your body weight can significantly reduce liver fat and inflammation. Regular exercise improves insulin sensitivity and helps clear liver fat even before the scale moves much. Given how common this condition is, those straightforward interventions have the potential to help hundreds of millions of people worldwide.