Abstract Background Recent studies have indicated that a ketogenic diet can be used as an adjuvant therapy to enhance sensitivity to chemotherapy and radiotherapy in cancer patients. However, there are no sufficient data and no consistent international treatment guidelines supporting a ketogenic diet as an adjuvant therapy for metastatic breast cancer. Therefore, this trial was designed to observe whether irinotecan with a ketogenic diet can promote sensitivity to chemotherapy and remit target lesions in locally recurrent or metastatic Her-2-negative breast cancer patients. Methods/design This trial aims to recruit 518 women with locally recurrent or metastatic breast cancer admitted to the Liaoning Cancer Hospital and Institute (Shenyang, China) in northeast China. All patients will be randomly assigned into the combined intervention group (n = 259) or the control group (n = 259), followed by treatment with irinotecan + ketogenic diet or irinotecan + normal diet, respectively. The primary endpoints are sensitivity to irinotecan and the objective response rate of target lesions; the secondary endpoints include quality of life scores (EORTC QLQ-C30), progression-free survival, overall survival time, incidence of adverse events, and cost-effectiveness. The endpoints will be evaluated at baseline (before drug administration), during treatment, 4 weeks after treatment completion, and every 3months (beginning 2 months after treatment completion). Discussion This trial attempts to investigate whether irinotecan treatment with a ketogenic diet for locally recurrent or metastatic breast cancer among women in northeast China can enhance the disease’s sensitivity to chemotherapy and reduce target lesions. Trial registration Chinese Clinical Trial Registry, ID: ChiCTR1900024597. Registered on 18 July 2019. Protocol Version: 1.1, 24 February 2017.