Abstract Obesity is associated with gut dysbiosis, chronic inflammation, and insulin resistance. We assessed proportional change in fecal microbial populations in a pilot study (n=34) of peri/postmenopausal women with BMI ≥28 kg/m2 who were randomized to receive either 3.25 g/day of omega-3 fatty acids or a placebo during a weight loss intervention. Body composition was assessed using DXA, and fecal and blood samples were collected. Median weight change was -10%. Among participants who lost ≥10% of their weight, those assigned to omega-3 fatty acids showed the greatest decrease in the Firmicutes/Bacteroidetes phyla ratio and displayed favorable changes in systemic biomarkers. Notable increases in the proportional abundance of short-chain fatty acid (SCFA)-producing microbes including Phocaeicola vulgatus and Alistipes putredinis were observed in women receiving omega-3, which correlated with improvements in breast cancer biomarkers such as bioavailable estradiol, adiponectin-to-leptin ratio, and C-reactive protein levels. Women administered omega-3 fatty acids displayed increased % change in plasma SCFA propionate and decreased butyrate, suggesting intervention differentially modulated circulating bacterial-derived SCFA metabolites. High dose omega-3 fatty acids, when added to a behavioral weight loss intervention, promoted beneficial shifts to the gut microbiome and associated with improved breast cancer risk factors biomarkers.
Cook et al. (2026) studied this question.