Low vs. High Glycemic Diets: Comparative Effects on Gut-Brain Axis Modulation and Psychological Well-Being

The relationship between dietary patterns, gut microbiota, and psychological health has emerged as a critical area of research, particularly in understanding how carbohydrate quality, measured by the glycemic index (GI), influences the gut-brain axis (GBA) and mental well-being. This review explores the comparative effects of low- versus high-GI diets on key metabolic parameters, gut integrity, systemic inflammation, cognitive performance, and psychological health outcomes. Low-GI diets are consistently associated with improved blood glucose regulation, enhanced insulin sensitivity, reduced systemic inflammation, and better gut barrier function, collectively contributing to improved physical and mental health. They promote a more favorable gut microbiota composition, stimulate beneficial neurotransmitter production, and strengthen blood-brain barrier integrity, thereby supporting cognitive function and emotional stability. Conversely, high-GI diets are linked to gut dysbiosis, elevated inflammatory markers, glycemic volatility, and an increased risk of mood disorders such as depression and anxiety. These diets exacerbate metabolic disturbances, contribute to obesity, type 2 diabetes, and cardiovascular diseases, and may impair neurocognitive functions via inflammatory and oxidative stress pathways. Animal and human studies alike underscore that high-GI diets can cause greater fat accumulation, disrupt glucose-insulin homeostasis, and impair gut and brain health, whereas low-GI diets offer protective effects. Nevertheless, methodological inconsistencies such as variations in meal composition, duration of interventions, participant demographics, and cognitive assessment tools limit the ability to draw definitive conclusions. Future research should prioritize standardized study designs, long-term follow-ups, and integrative omics approaches to better elucidate the mechanisms underlying these relationships. Clinically, promoting low-GI, minimally processed, nutrient-rich foods may serve as an effective strategy for mitigating both metabolic and psychological disorders.