A 70-year-old woman with no history of diabetes was admitted to the hospital for the management of hypoglycemia. Her fasting plasma glucose level was 54 mg/dL with an extremely high serum immunoreactive insulin level (1,210 μU/mL). She had high titers of anti-insulin antibodies and exhibited the DRB1*0406 genotype for HLA-DR4, leading to a diagnosis of insulin autoimmune syndrome. She had been taking several health preparations for approximately 10 years; however, all were thiol group-free. Due to frequent episodes of nocturnal hypoglycemia, the health preparations were discontinued and the patient was treated with cornstarch. This protocol successfully ameliorated the hypoglycemic episodes and normalized the patient's laboratory and serological test results.