Background: Breast Cancer (BC) patients often ask for a healthy diet. Here, we compared three different diets which could support BC patients during the rehabilitation process: a healthy standard diet (SD), a low carb diet (LCD) and a ketogenic diet (KD).Patients and Methods:KOLIBRI was a one-site nutritional intervention trial, combining inpatient and outhouse phases for 20 weeks. Female BC patients (n=152; mean age 51.7 years) could select their diet. Data collected were: quality of life (QoL), spiroergometry, body composition, blood biochemistry. 30, 92 and 30 patients started the KD, LCD and SD, respectively. Of those, 20, 72 and 25 completed the final examination.Results:Patients rated all diets as feasible in daily life. No adverse effects occurred in any diet group. KD offered the highest amount of energy and protein. All groups improved in QoL, body composition and physical performance. KD was superior in improving fatigue, insomnia and physical functioning. KD participants finished with the best physical performance and the highest muscle/fat ratio. Despite their increased cholesterol, KD patients had the best triglyceride/HDL ratio and HOMA-IR. Most metabolic parameters significantly improved in the LCD group. SD participants ended with remarkably low cholesterol levels, but did not improve triglyceride/HDL or HOMA-IR.Conclusions:A well-defined KD and LCD are safe and beneficial for BC. Both diets could thus be recommended for patients wanting to self-support their rehabilitation process.Trial registration IDNCT02092753 Protocol Registration date:02/26/2014Ketogenic Or LOGI Diet In a Breast Cancer Rehabilitation Intervention (KOLIBRI)URL: https://clinicaltrials.gov/ct2/show/NCT02092753?cond=KOLIBRI&draw=2&rank=1