脂肪肝は生活習慣病の一つであり，その有病率は成人の約30％を占めている．近年，世界的に脂肪性肝疾患からの肝がんは増加しており，大きな健康問題となっている．これらの肝がんは，ウイルス性肝がんのように炎症から線維化，発がんという病態進展様式に該当せず，発がんに多くの要因が関与している．これまで非アルコール性脂肪肝炎（NASH）という病名が用いられて来たが，2023年欧米の肝臓病学会主導で新たな病名（MASLD/MASH）が提唱された．この中で，中等量の飲酒をする患者集団はMetALDとして規定され，心血管代謝リスクと中等量飲酒の影響を併せて検討することが可能となった．本シンポジウムでは，MASLD/MASHを脂肪肝と栄養代謝異常を病態形成の根幹とする進行性肝疾患として捉え直し，特にMetALDをテーマとして，病名変更によるインパクトを疫学，病態，診断，治療開発の観点から日米の立場から議論を深めたい．

Fatty liver is a lifestyle-related disease with a prevalence of approximately 30% of adults. In recent years, liver cancer from fatty liver disease has increased worldwide and has become a major health problem. Many factors are involved in the carcinogenesis of fatty liver disease, which is distinct from that of virus hepatitis-related liver cancer. In 2023, the nomenclature of NAFLD/NASH was changed to MASLD/MASH, which was led by the initiative of the AASLD, EASL, and ALEH. Within this, the group of patients with steatotic liver disease who drink moderate amounts of alcohol was defined as MetALD, which allowed us to study the combined effects of cardio-metabolic risk factors and moderate alcohol consumption on liver disease progression. In this symposium, MASLD/MASH is redefined as a progressive liver disease with steatosis and metabolic dysfunction, and the impact of the nomenclature change will be discussed on MetALD from the perspective of epidemiology, pathogenesis, diagnosis, and treatment development in Japan and the US.