A 58‐year‐old women who was diagnosed with type 2 diabetes 20 years earlier had been treated with antidiabetic medicines since she was aged 40 years. After sodium–glucose cotransporter 2 inhibitors administration, her bodyweight rapidly decreased from 40 to 30 kg over a period of 3 weeks. She had abdominal symptoms, including nausea, especially after a meal. On admission, physical examinations and laboratory data showed euglycemic ketoacidosis, dehydration and low insulin secretion levels. Additionally, abdominal contrast computed tomography showed the finding of superior mesenteric artery syndrome. This case urges caution, including rapid excessive bodyweight loss and euglycemic ketoacidosis, on the use of sodium–glucose cotransporter 2 for lean diabetes patients.