Low Glycemic Index Scarlet Runner Bean-Based Multi-Grain Meal Replacement Powder Improves Metabolic Disorders and Gut Dysbiosis in T2DM Rats

Low glycemic index (GI) diets play a pivotal role in the prevention and management of type 2 diabetes mellitus (T2DM). This study investigated the effects of a low GI multigrain meal replacement powder, primarily composed of scarlet runner beans (Phaseolus coccineus L.), on glycolipid metabolic disorders and gut dysbiosis in T2DM rats. A T2DM rat model was induced by a high-fat diet combined with streptozotocin, and rats were randomized into model control (MC), positive control (PC), low-, medium-, and high-dose intervention (LD/MD/HD) and normal control (NC) groups based on fasting blood glucose and body weight. After 8 weeks of intervention, the powder significantly ameliorated glycolipid dysmetabolism, attenuated inflammatory responses, and reduced histopathological damage in T2DM rats. Compared with MC, all intervention groups showed reduced fasting blood glucose (FBG), glycated hemoglobin (HbA1c), and glucagon, along with increased insulin (INS) and glucagon-like peptide-1 (GLP-1) (P < 0.05). The HD group further reduced the serum total cholesterol (TC), triglycerides (TG), low-density lipoprotein cholesterol (LDL-C), and non-esterified fatty acids (NEFA), while increasing high-density lipoprotein cholesterol (HDL-C) (P < 0.05). The MD group also decreased serum TG and LDL-C and increased HDL-C (P < 0.05). Pro-inflammatory cytokines (IL-6, IL-1β) were suppressed, whereas transforming growth factor-β (TGF-β) was upregulated in all intervention groups (P < 0.05). The intervention also restored gut microbial homeostasis, characterized by increased abundances of short-chain fatty acids (SCFA)-producing genera (Intestinimonas, Lachnospiraceae_NK4A136_group, Ruminococcus) and reduced levels of potentially pathogenic genera (Allobaculum, Faecalibaculum) (P < 0.05). Fecal SCFA concentrations increased in all intervention groups, with acetic acid significantly elevated in LD (P < 0.05). These findings suggest that this low GI meal replacement powder improves metabolic dysregulation, alleviates inflammation and tissue injury, and restores gut microbiota balance in T2DM, supporting its potential utility in T2DM management.