Using mouse genetics, histology, liver damage assays and transcriptomics we discovered that iron deficiency arising from KCNE2-dependent achlorhydria is a major factor in early-onset NAFLD in Kcne2─/─ mice, while two other KCNE2-dependent defects did not initiate NAFLD. This evidence concerns the gene KCNE2 and metabolic dysfunction-associated steatotic liver disease.