Hepatic steatosis is the medical term for excess fat stored in liver cells. It’s the earliest stage of what’s now called metabolic dysfunction-associated steatotic liver disease (MASLD), and it affects roughly 1.3 billion people worldwide, about 16% of the global population as of 2023. In most cases, it produces no symptoms at all, which is why many people first hear the term after a routine imaging scan or blood test flags something unexpected.
How Fat Builds Up in the Liver
Your liver normally processes fats and carbohydrates from your diet, burning some for energy and packaging the rest into particles that get shipped out to other tissues. Hepatic steatosis develops when more energy flows into the liver than it can burn off or export. The surplus gets stored as fat droplets inside liver cells called hepatocytes.
Several things can tip this balance. The liver can take in too much dietary fat, convert too many carbohydrates into new fat (a process called de novo lipogenesis), or struggle to export fat efficiently. Fructose plays a particularly notable role here: unlike glucose, which gets metabolized throughout the body, fructose is processed almost entirely in the liver. It bypasses the normal regulatory checkpoints that limit how fast carbohydrates get turned into fat. Worse, when the liver is actively converting carbohydrates to fat at a high rate, it simultaneously blocks its own ability to burn existing fatty acids for energy. The result is a double hit: more fat production, less fat burning.
Genetic factors also matter. Some people inherit variations that make their liver less efficient at breaking down stored fat or at assembling the transport particles needed to move fat out of liver cells. These genetic differences help explain why some people develop steatosis even without the typical metabolic risk factors.
The Name Change: From NAFLD to MASLD
If you’ve seen the terms NAFLD or “non-alcoholic fatty liver disease” before, those names are being phased out. In 2023, major liver disease organizations adopted new terminology. “Steatotic liver disease” is now the umbrella term for any condition involving liver fat, regardless of cause. The most common form, previously called NAFLD, is now MASLD.
To qualify as MASLD, a person needs evidence of liver fat plus at least one of five cardiometabolic risk factors: being overweight or having a large waist circumference, elevated blood sugar or type 2 diabetes, high blood pressure, high triglycerides, or low HDL cholesterol. In practice, this captures the vast majority of people with fatty liver, since metabolic factors drive most cases. A separate category called MetALD covers people who have MASLD and also drink moderate-to-heavy amounts of alcohol.
Symptoms and Early Warning Signs
Hepatic steatosis on its own rarely causes noticeable symptoms. Most people feel completely fine. When symptoms do appear, they tend to be vague: persistent 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 stress, poor sleep, or dozens of other causes, which is one reason the condition often goes undetected for years.
More obvious symptoms like yellowing of the skin, abdominal swelling, or easy bruising typically don’t show up until the disease has progressed well beyond simple fat accumulation into advanced scarring or cirrhosis.
How Steatosis Progresses
Not everyone with hepatic steatosis will develop serious liver problems, but the condition does carry real risk. The progression follows a general pattern:
- Simple steatosis: Fat is present in liver cells, but there’s no significant inflammation or damage. Many people stay at this stage indefinitely.
- Steatohepatitis (MASH): The liver becomes inflamed and liver cells start to get damaged. This was previously called NASH. It’s a critical turning point because inflammation drives scarring.
- Fibrosis: Scar tissue begins replacing healthy liver tissue. Fibrosis is graded on a scale from F0 (no scarring) through F4 (cirrhosis). The fibrosis stage is the single most important factor in determining long-term outcomes.
- Cirrhosis (F4): Extensive scarring disrupts the liver’s structure and function. At this point, complications like liver failure and liver cancer become real concerns.
The transition from simple steatosis to steatohepatitis is what doctors most want to prevent, because once inflammation and scarring begin, reversing the damage gets progressively harder.
How It’s Diagnosed
Hepatic steatosis is most commonly spotted on an abdominal ultrasound, often one ordered for an unrelated reason. Standard ultrasound is widely available and inexpensive, and newer quantitative ultrasound techniques can estimate liver fat percentage with reasonable accuracy, showing a sensitivity of about 94% for detecting clinically meaningful fat levels.
For more precise measurement, MRI-based techniques can quantify liver fat down to exact percentages. A liver fat fraction of 5.5% or higher on MRI is the standard threshold for diagnosing steatosis. This is considered the gold standard for fat measurement, though it’s more expensive and not always necessary for an initial diagnosis.
Elastography, either ultrasound-based or MRI-based, measures liver stiffness to estimate how much scarring is present. This is especially important for determining whether simple steatosis has progressed to fibrosis. Liver biopsy remains the most definitive way to assess inflammation and scarring, but it’s invasive and typically reserved for cases where the degree of damage is uncertain from imaging alone.
What Causes It
The core metabolic risk factors overlap heavily with metabolic syndrome. Insulin resistance is the central driver for most people: when cells don’t respond well to insulin, the body compensates by producing more, which promotes fat storage in the liver. Excess body weight, particularly visceral fat around the midsection, strongly correlates with liver fat accumulation. High triglycerides, low HDL cholesterol, elevated blood sugar, and high blood pressure all cluster together as both causes and consequences of the same metabolic dysfunction.
Diet composition matters independently of total calories. Diets high in added sugars (especially fructose from sweetened beverages), refined carbohydrates, and saturated fats promote liver fat even before significant weight gain occurs. Sedentary behavior compounds the problem by reducing the muscles’ ability to burn fat and glucose, leaving more surplus for the liver to handle.
Reversing Liver Fat
The good news is that hepatic steatosis is highly reversible in its earlier stages. Weight loss is the most effective intervention. Losing just 3 to 5 percent of body weight is typically enough for fat to start clearing from liver cells. For someone weighing 200 pounds, that’s 6 to 10 pounds. To improve inflammation and scarring, a larger loss of about 10 percent of body weight is generally needed.
No specific diet has been proven superior, but patterns that reduce sugar intake (particularly sugary drinks), limit refined carbohydrates, and emphasize whole foods consistently show benefits. The Mediterranean dietary pattern has the strongest evidence base. Regular physical activity helps even without weight loss by improving insulin sensitivity and promoting fat burning in the liver.
The First Approved Medication
In March 2024, the FDA approved the first medication specifically for liver scarring caused by fatty liver disease. Called Rezdiffra, it works by partially activating a thyroid hormone receptor in the liver, which helps the liver burn off stored fat. It’s approved for adults with steatohepatitis and moderate to advanced fibrosis (F2 or F3), to be used alongside diet and exercise.
In clinical trials, 24 to 36 percent of people taking the medication achieved resolution of their liver inflammation without worsening of scarring, compared to 9 to 13 percent on placebo. Roughly 24 to 28 percent saw improvement in their scarring, compared to 13 to 15 percent on placebo. The most common side effects were diarrhea and nausea. It’s not appropriate for people who already have advanced cirrhosis. The approval came through the FDA’s accelerated pathway, meaning continued study is required to confirm long-term benefit.
Why It Matters Beyond the Liver
Hepatic steatosis isn’t just a liver problem. The leading cause of death in people with MASLD is actually cardiovascular disease, not liver failure. The same metabolic dysfunction that drives fat into the liver also accelerates plaque buildup in arteries, raises blood pressure, and promotes chronic low-grade inflammation throughout the body. People diagnosed with hepatic steatosis have a meaningfully higher risk of heart attack and stroke compared to the general population, which makes addressing the underlying metabolic issues important for far more than just the liver.
Type 2 diabetes and fatty liver disease also reinforce each other. Insulin resistance promotes liver fat, and liver fat worsens insulin resistance, creating a cycle that can be difficult to break without deliberate lifestyle changes. Addressing one condition almost always improves the other.