The Duodenum-Centered Neurohormonal Hypothesis of Type 2 Diabetes: A Mechanistic Review and Therapeutic Perspective

Type 2 diabetes mellitus (T2DM) is a multifactorial disorder defined by insulin resistance, β-cell dysfunction, and chronic hyperglycemia. Although peripheral mechanisms have been extensively studied, increasing evidence implicates the gastrointestinal tract in disease onset. Insights from bariatric surgery, gut hormone signaling, and incretin-based therapies suggest that the gut contributes actively beyond nutrient absorption. Yet, a cohesive framework integrating these observations remains absent, leaving a critical gap in our understanding of T2DM's upstream pathophysiology. This work builds upon the anti-incretin theory, which posits that nutrient-stimulated neurohormonal signals-termed "anti-incretins"-arise from the proximal intestine to counteract incretin effects and regulate glycemic homeostasis. The excess of anti-incretin signals, perhaps stimulated by macronutrient composition or chemical additives of modern diets, disrupts this balance and may cause insulin resistance and β-cell depletion, leading to T2D. We hypothesize that the neuroendocrine signals produced by cholecystokinin (CCK)-I and secretin-S cells, both located in the proximal intestine, function as endogenous anti-incretins. In this context, we hypothesize a novel model centered on the chronic overstimulation of I and S cells by high-fat, high glycemic index modern diets. This drives what we term "amplified digestion"-a state marked by heightened vagal and hormonal stimulation of biliary and pancreatic secretions, increased enzymatic and bile acid activity, and alterations in bile acid composition. This condition leads to an extended breakdown of carbohydrates, lipids, and proteins into absorbable units, thereby promoting excessive nutrient absorption and ultimately contributing to insulin resistance and progressive β-cell failure. Multiple lines of clinical, surgical, and experimental evidence converge to support our model, rooted in the physiology of digestion and absorption. Western dietary patterns appear to induce an over-digestive adaptation-marked by excessive vagal and hormonal stimulation of biliary and pancreatic secretion-which amplifies digestive signaling. This heightened state correlates with increased nutrient absorption, insulin resistance, and β-cell dysfunction. Interventions that disrupt this maladaptive signaling-such as truncal vagotomy combined with duodenal bypass-may offer novel, physiology-based strategies for T2DM treatment. This hypothesis outlines a potential upstream contributor to insulin resistance and T2DM, grounded in digestive tract-derived neurohormonal dysregulation. This gut-centered model may provide insight into early, potentially reversible stages of the disease and identify a conceptual therapeutic target. Nonetheless, both the hypothesis and the accompanying surgical strategy-truncal vagotomy combined with proximal intestinal bypass-remain highly exploratory and require systematic validation through mechanistic and clinical studies. Further investigation is warranted to clarify the molecular regulation of I and S enteroendocrine cells, including the genetic and epigenetic factors that may drive hypersecretion. While speculative, interventions-surgical or pharmacologic-designed to modulate these digestive signals could represent a future avenue for research into T2DM prevention or remission, pending rigorous evidence.