Steatohepatosis, usually called fatty liver, is the build-up of fat inside liver cells, defined by convention as visible fat in more than 5 percent of them. It is the fat-only stage, before visible inflammation. When inflammation and injured, swollen liver cells appear alongside the fat, the diagnosis becomes steatohepatitis. Most cases are metabolic rather than alcoholic, and guidelines are replacing the label NAFLD with MASLD, metabolic dysfunction-associated steatotic liver disease.
What it measures
It describes a state of tissue, not a number from a blood tube. The reference standard is a liver biopsy, where a pathologist counts how many liver cells hold fat, but it is invasive and rarely justified for fat alone. Most diagnoses come from imaging, as set out in the fuller reference entry for Steatohepatosis (fatty liver).
Abdominal ultrasound is the usual first look: a fatty liver appears brighter than the kidney beside it. It is cheap and safe but misses mild fat and depends on the operator. The controlled attenuation parameter, read on the same device as liver stiffness, gives a numeric estimate, and MRI proton density fat fraction measures liver fat most accurately without a needle. Blood tests only support the picture: enzymes are often normal even with substantial liver fat, so a normal ALT does not rule the condition out.
Typical values
Thresholds depend on the method, and imaging estimates are not interchangeable with each other or with biopsy. The bands below are grading conventions, not personal cut-offs.
| Method | What it reports | How to read it |
|---|---|---|
| Biopsy grade | Share of liver cells holding fat | Under 5 percent is normal; bands run mild, moderate, severe |
| MRI fat fraction | Percent fat by MRI | About 5 percent and above counts as steatosis; tracks change well |
| Ultrasound | Brightness of the liver | Reported as mild, moderate or marked; qualitative, operator-dependent |
| Attenuation parameter | Ultrasound signal loss through fat | Rises with fat; cut-offs differ by device and probe |
| Liver enzymes | ALT, AST, GGT in blood | Often normal; limits differ by lab, sex and assay |
Why it matters for longevity
Fatty liver is common, with global estimates of roughly a quarter to a third of adults, and it travels with Insulin resistance, central fat and high triglycerides. In observational cohorts it is associated with a higher risk of type 2 diabetes, cardiovascular disease, chronic kidney disease and some cancers. Because it clusters with excess weight and inactivity, those studies cannot separate the fat from the company it keeps.
Two points are consistent. The leading cause of death here is cardiovascular disease, not liver failure, so the finding reads best as a whole-body metabolic signal. And what predicts mortality most strongly is not the amount of fat but the amount of scarring, which is why clinicians move quickly from a fatty liver report to a fibrosis estimate. Fat alone is often reversible; the progression to NASH — non-alcoholic steatohepatitis and then to fibrosis and cirrhosis is what carries the risk.
What changes it
Weight loss is the best-supported lever, and it works in steps: a modest loss reduces liver fat, a larger loss is usually needed before inflammation improves, and only substantial sustained loss has been linked to less scarring. Exercise lowers liver fat even when the scale barely moves, with both aerobic and resistance training. On the plate, cutting sugar-sweetened drinks and refined starch matters more than trimming total fat, because excess calories and fructose drive fat production inside the liver.
Alcohol adds to the same injury and should be cut back or dropped. Coffee intake is associated with less liver fat and less fibrosis in observational data. Drug treatment now exists for the inflammatory stage with fibrosis, and GLP-1 receptor agonists reduce liver fat in trials, but those are prescription decisions. Genetic variants such as PNPLA3 raise susceptibility and cannot be changed, which is why some lean people develop fatty liver and some heavier people do not.
Related reading
- How to Improve Metabolic Health: A Practical Guide
- Which Blood Tests Reflect Aging and How to Read Them
- Glycation and AGEs: How Sugar Ages Your Tissues
- Visceral fat
Disclaimer. This article is for information only and does not replace medical advice. Talk to a qualified clinician before changing anything about your health.