This randomized pilot trial (n = 34) investigated whether adding high-dose omega-3 polyunsaturated fatty acids to a behavioral weight-loss program would modulate the gut microbiome and related metabolites in peri- and postmenopausal women with elevated adiposity and increased breast cancer risk. Participants had body mass index (BMI) ≥28 kg/m2 and were randomized to receive either 3.25 g/day of omega-3 fatty acids (eicosapentaenoic acid/docosahexaenoic acid) or placebo during the weight-loss intervention. The primary focus reported in the abstract was proportional change in fecal microbial populations and associations with circulating metabolites and breast cancer–related biomarkers.
The study enrolled peri- and postmenopausal women with BMI ≥28 kg/m2. Randomization allocated participants to receive either 3.25 g/day omega-3 or placebo while undergoing a behavioral weight-loss program. Body composition was assessed using dual X-ray absorptiometry (DXA). Fecal and blood samples were collected at baseline and follow-up for microbiome and biomarker analyses. The median weight change reported for the cohort was −10%.
Key assessments described in the abstract included:
Body composition by DXA, fecal microbial composition, circulating SCFAs, and breast cancer risk biomarkers formed the principal outcome measures reported in the abstract.
Among participants who achieved ≥10% weight loss, those randomized to omega-3 supplementation exhibited the greatest decrease in the Firmicutes:Bacteroidetes ratio. The omega-3 group also showed notable increases in the proportional abundance of specific short-chain fatty acid (SCFA)-producing microbes, particularly Phocaeicola vulgatus and Alistipes putredinis, compared with placebo. These taxa-level shifts are presented in the abstract as being linked to the intervention effect when combined with clinically meaningful weight loss (≥10%).
Plasma SCFA profiling in the trial revealed that women receiving omega-3 displayed an increased percent change in circulating propionate and a decreased percent change in butyrate. The abstract reports these changes as suggesting that the intervention differentially modulated circulating bacteria-derived SCFA metabolites. The observed increase in propionate alongside enrichment of propionate-associated taxa supports a connection between the microbiome shifts and systemic SCFA levels.
Changes in the microbiome and SCFAs among women receiving omega-3 correlated with favorable trends in biomarkers linked to breast cancer risk. Specifically, increases in SCFA-producing microbes were associated with improvements in bioavailable estradiol, a higher adiponectin:leptin ratio, and lower C-reactive protein (CRP) levels. The abstract frames these biomarker changes as relevant to the mechanistic pathway by which weight loss and omega-3 may reduce obesity-associated breast cancer risk through modulation of inflammation, adipokines, and metabolite production by the gut microbiome.
The authors conclude that adding high-dose omega-3 fatty acids to a behavioral weight-loss intervention promoted beneficial shifts in the gut microbiome and was associated with improved systemic biomarkers of breast cancer risk. The trial emphasizes prevention relevance: since obesity is a modifiable risk factor for breast cancer characterized by chronic inflammation and altered adipokines, interventions that both reduce adiposity and target underlying metabolic and inflammatory drivers may enhance risk reduction. In this study, omega-3 supplementation shifted SCFA-producing microbiota, increased circulating propionate, and correlated with favorable changes in bioavailable estradiol, adiponectin:leptin ratio, and CRP.
The PubMed abstract reports key findings but does not include several methodological and quantitative details that would be required to fully evaluate the trial, including exact randomization procedures, allocation concealment, blinding, full statistical methods, magnitude and statistical significance values for reported changes, safety or adverse events, and longer-term follow-up. These specifics are available in the full-text article but were not reported in the abstract. Readers should consult the full publication for comprehensive methods, complete numerical results, and detailed discussion of limitations.
All observations summarized here are taken from the PubMed abstract. The trial is described as a randomized controlled pilot study; sample size and subgroup analyses (for participants with ≥10% weight loss) are reported in the abstract. Associations between microbiome composition, circulating SCFAs, and breast cancer risk biomarkers are correlational within the context of the intervention. The abstract frames the results in the context of obesity-related mechanisms relevant to breast cancer prevention and suggests that targeting the gut microbiome with omega-3 in the setting of weight loss may be a promising strategy.
The trial is published in Cancer Prevention Research (Phila) with DOI 10.1158/1940-6207.CAPR-26-0021 and PubMed ID 41999613. For full methodological detail, statistical analyses, and complete results, consult the full text at the journal or the PubMed full-text links.