Long-term intermittent caloric restriction remodels the gut microbiota in mice genetically prone to breast cancer

•Caloric restriction can remodel gut microbiota that is predisposed to breast cancer.•Intermittent caloric restriction modifies age-related microbial changes.•Regardless of diet, genetic predisposition contributes gut microbiota dysbiosis. Compared with ad libitum control and chronic caloric-restricted groups, the long-term application of intermittent caloric restriction to a mouse mammary tumor-transforming growth factor-alpha transgenic breast cancer mouse model increases microbial diversity and modifies the age-related compositional changes, which are potential contributors to mammary tumor development. [Display omitted] Gut microbiota dysbiosis is among the risk factors for breast cancer development, together with genetic background and dietary habits. However, caloric restriction has been shown to remodel the gut microbiota and slow tumor growth. Here, we investigated whether the gut microbiota mediates the preventive effects of long-term chronic or intermittent caloric restriction on breast cancer predisposition. 10-week-old transgenic breast cancer-prone mice were randomly assigned to dietary groups (ad libitum, chronic caloric restriction, and intermittent caloric restriction groups) and fed up to week 81. Stool samples were collected at weeks 10 (baseline), 17 (young), 49 (adult), and 81 (old). 16S rRNA gene sequencing was performed to identify the gut microbiota profile of the different groups. In order to investigate the breast cancer gut microbiota profile within genetically predisposed individuals regardless of diet, mammary tumor-bearing mice and mammary tumor-free but genetically prone mice were selected from the ad libitum group (n = 6). Intermittent caloric restriction increased the microbial diversity of adult mice and modified age-related compositional changes. A total of 13 genera were differentially abundant over time. Pathogenic Mycoplasma was enriched in the re-feeding period of the old intermittent caloric restriction group compared with baseline. Furthermore, mammary tumor-free mice showed shared gut microbiota characteristics with mammary tumor-bearing mice, suggesting an early link between genetic predisposition, gut microbiota, and breast cancer development. Our study revealed the role of gut microbes in the preventive effects of caloric restriction against breast cancer development, implying the significance of diet and microbiome interplay.