BackgroundLow-carbohydrate diet (LCD) is an emerging therapy for type 2 diabetes mellitus (T2DM). Although its effect on glucose control has been confirmed in previous clinical trials, most of those studies have focused on comparing calorie-restricted LCD to iso-caloric low-fat diets. In this study, we aim to compare the effects of LCD and canagliflozin, a sodium-glucose cotransporter 2 inhibitor, in patients with T2DM.MethodsThis is a multicenter, randomized controlled trial. We will recruit 120 patients with poor-controlled T2DM. Participants will be randomly divided into canagliflozin and LCD groups in a 1:1 ratio. The primary outcome is the change in hemoglobin A1C levels after the 3-month intervention. The secondary outcomes are the time in range and cost of antihyperglycemic agents. Exploratory outcomes include physical examination, body composition, glucose variability, appetite, glycolipid metabolism, liver lipid content, and urine glucose threshold.DiscussionNo previous study has compared an LCD with antihyperglycemic agents. In LoCaT, participants’ metabolism will be assessed from multiple perspectives. It is believed that the finding obtained from this trial will optimize the treatments for patients with T2DM.Trial registrationChinese Clinical Trial Registry ChiCTR1900027592. Registered on November 20, 2019.Supplementary InformationThe online version contains supplementary material available at 10.1186/s13063-023-07427-5.