Varietal Differences in Kidney Beans Modulate Gut Microbiota and Inflammation During High-Fat Diet-Induced Obesity in Male Mice

Background: Obesity-associated inflammation arises from adipose dysfunction and intestinal disturbances, including altered microbiota and short-chain fatty acid (SCFA) metabolism. Beans (Phaseolus vulgaris) are rich in non-digestible carbohydrates and polyphenols, but whether kidney bean varieties differing in seed coat colour exert distinct effects on inflammation in obesity remains unclear. Objective: To determine whether supplementation of an obesogenic high-fat (HF) diet with white or dark red kidney beans modulates gut microbiota, SCFAs, and intestinal, systemic, and neuroinflammatory outcomes. Methods: Male C57Bl/6N mice (n = 12/group) were fed a basal diet (BD; modified AIN-93G), an HF diet (60% kcal from fat), or an HF diet supplemented with 15% cooked white (HF + WK) or dark red kidney beans (HF + DK) for nine weeks. Outcomes included cecal microbiota composition, predicted KEGG pathways with taxon contributors mapped with BURRITO (a tool for linking predicted microbial functions to contributing taxa), and SCFA-related pathways; cecal and fecal SCFA concentrations; colon histomorphometry and expression of gut barrier junction and inflammatory genes; serum cytokines and adipose hormones; and hippocampal inflammatory and barrier genes. Results: Mice consuming bean-supplemented HF diets had higher microbial diversity, enrichment of SCFA-producing taxa (Prevotella, Lactobacillus, Muribaculaceae), and lower obesity-associated genera versus HF alone (Mucispirillum, rc4-4). Bean diets elevated cecal acetate and butyrate concentrations, which aligned with increases in predicted acetate kinase in both bean groups versus HF and BD, and butyrate kinase in HF + DK versus BD. Bean supplementation attenuated HF-induced reduction of goblet cells and systemic interleukin (IL)-10. The HF + DK group had lower colonic tumour necrosis factor (TNF)-α and partially attenuated hippocampal IL-6. SCFAs were inversely associated with systemic and neuroinflammatory markers in HF + DK mice. Conclusions: Kidney bean supplementation mitigated HF diet-induced intestinal, systemic, and neuroinflammatory disturbances in male mice, with microbiota and SCFA modulation. Further, dark red beans exerted stronger anti-inflammatory effects, highlighting the role of seed coat colour in bean-mediated obesity outcomes.