Health-related quality of life is associated with fecal microbial composition in breast cancer survivors

Purpose To investigate relationships between body size, gut microbiome, and health-related quality of life (QOL) in breast cancer survivors (BCS) in a clinical trial. Methods A cross-sectional substudy was conducted using baseline data from 70 BCS participating in a randomized controlled trial of a lifestyle intervention. Measures included anthropometrics, QOL (Short Form Health-related QOL Survey-36 [SF-36]), and 16S rRNA gene sequencing of fecal microbes. Participants were categorized by body mass index (BMI) into without obesity (≤ 29.9 kg/m 2 ; n = 38) and with obesity (≥ 30.0 kg/m 2 ; n = 32) groups. Differences in bacterial taxa between groups were assessed using Kruskal–Wallis one-way analysis of variance. Spearman and partial correlations explored associations between taxa and SF-36 subscales. Mediation analysis explored the relationship between BMI and SF-36 mental health summary score with alpha diversity as a mediator. Results Most BCS (72.9%) were non-Hispanic White with average age of 61.6 (± 8.7) years. No differences were observed for SF-36 subscales between groups. Physical functioning, vitality, and mental health subscales were negatively associated with Ruminococcus (ρ = − 0.304, p = 0.036; ρ = − 0.361, p = 0.012; ρ = − 0.495, p