Intermittent Fasting in Breast Cancer: A Systematic Review and Critical Update of Available Studies.

Breast cancer (BC) is the most-frequent malignancy amongst women, whereas obesity and excess caloric consumption increase the risk for developing the disease. The objective of this systematic review was to examine the impact of intermittent fasting (IF) on previously diagnosed BC patients, regarding quality of life (QoL) scores during chemotherapy, chemotherapy-induced toxicity, radiological response and BC recurrence, endocrine-related outcomes, as well as IF-induced adverse effects in these populations. A comprehensive search was conducted between 31 December 2010 and 31 October 2022, using the PubMed, CINAHL, Cochrane, Web of Science, and Scopus databases. Two investigators independently performed abstract screenings, full-text screenings, and data extraction, and the Mixed Method Appraisal Tool (MMAT) was used to evaluate the quality of the selected studies. We screened 468 papers, 10 of which were selected for data synthesis. All patients were female adults whose age ranged between 27 and 78 years. Participants in all studies were women diagnosed with BC of one of the following stages: I, II (HER2-/+), III (HER2-/+), IV, LUMINAL-A, LUMINAL-B (HER2-/+). Notably, IF during chemotherapy was found to be feasible, safe and able to relieve chemotherapy-induced adverse effects and cytotoxicity. IF seemed to improve QoL during chemotherapy, through the reduction of fatigue, nausea and headaches, however data were characterized as low quality. IF was found to reduce chemotherapy-induced DNA damage and augmented optimal glycemic regulation, improving serum glucose, insulin, and IGF-1 concentrations. A remarkable heterogeneity of duration of dietary patterns was observed among available studies. In conclusion, we failed to identify any IF-related beneficial effects on the QoL, response after chemotherapy or related symptoms, as well as measures of tumor recurrence in BC patients. We identified a potential beneficial effect of IF on chemotherapy-induced toxicity, based on markers of DNA and leukocyte damage; however, these results were derived from three studies and require further validation. Further studies with appropriate design and larger sample sizes are warranted to elucidate its potential standard incorporation in daily clinical practice.