For most of the past half-century, the chronic liver disease weighing on Chinese hospitals was viral. Hepatitis B was the prototype and the main burden.

Then vaccination arrived at scale. Mother-to-child transmission was blocked. Antiviral treatment became routine. On the Chinese account of the shift, the country's viral hepatitis burden has improved markedly.

Something else has been growing into the space that left behind.

The disease that replaced hepatitis B

Lifestyles changed first. Excess weight and metabolic disease stopped being exceptional. The condition long nicknamed the "disease of affluence" — fatty liver — has now overtaken viral hepatitis as China's most common chronic liver disease.

Two figures mark the ground it now covers. The National Health Commission puts the combined overweight and obesity rate among Chinese adults at 50.7%.

In 2025, the primary-care guideline for metabolic dysfunction-associated steatotic liver disease (MASLD) estimated prevalence in the general population at about 29.7%. That is roughly three people in every ten.

Three in ten is not a rounding error, and it is not a sub-group. It is the population average.

What three in ten looks like on a slide

The name is literal. Fat accumulates inside liver cells, and the cells fill with clear droplets that push the rest of their contents aside. On a stained section the change is visible at low power, which is why the condition is so often found by accident rather than by intent.

September 2026: 43.7% of 25,736 community adults

In September 2026, The Lancet Gastroenterology & Hepatology published a Chinese study that looked for liver fat in 25,736 community-dwelling adults. Steatotic liver disease was detected in 43.7% of them. Within that group, MASLD accounted for 39.5%.

The two figures are not describing the same thing. 29.7% is a prevalence estimate for the general population; 43.7% is what active screening found in a large community sample. Read together, they bracket how widely the condition is distributed.

It is not only a disease of the middle-aged and elderly

The 2025 guideline was written for adults. The paediatric data is sharper. A 2025 study of more than 16,000 Chinese children and adolescents who were overweight or obese found fatty liver in 43% of them — a prevalence that sits in the same range as the adult screening result, in a group far younger than the one the guideline was designed around.

The burden has changed places

Viral hepatitis receded because prevention and treatment were pushed out at scale. Fatty liver rose from the other direction, through the same shifts in body weight and metabolic health that the 50.7% headline describes. The order of the two has now flipped: fatty liver is the first chronic liver disease in China, and the numbers that displaced hepatitis B are the ones above — 29.7% of the general population, 43.7% of a screened community cohort, 43% of children and adolescents with obesity.

Fat is not abstract once you can see it. WWAI pairs a virtual microscope with an AI biology tutor, so you can ask questions about cells and tissues and then open a slide: including a human adipose tissue specimen stained with Sudan III, where the lipid droplets inside each fat cell stain orange-red and the nuclei sit squeezed against the cell wall. Search WWAI in your app store to begin.

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References

National Health Commission of the People's Republic of China. Report on Nutrition and Chronic Disease Status of Chinese Residents (2020).

Guideline for the diagnosis and management of metabolic dysfunction-associated steatotic liver disease in primary care (2025).

The Lancet Gastroenterology & Hepatology, September 2026 — community screening study of steatotic liver disease in 25,736 Chinese adults.