From nutrient-based to food-based assessment: the evolution of inflammatory indices and their significance for metabolic syndrome and type 3 diabetes mellitus

Chronic low-grade inflammation has emerged as the pivotal driver connecting metabolic syndrome (MetS) and type 2 diabetes mellitus (T2DM) to neurodegenerative disorders, a pathological continuum increasingly recognized as "Type 3 Diabetes Mellitus" (T3DM). Diet, as a primary modifiable lifestyle factor, plays a dual role as both an inflammatory trigger and a potential therapeutic target. This review systematically delineates the methodological evolution of dietary inflammatory indices, shifting from the reductionist, nutrient-centric logic of the Dietary Inflammatory Index (DII) to the systemic, "food-matrix-based" logic of the recently proposed Food Inflammation Index (FII). We provide an in-depth mechanistic synthesis of the gut-metabolism-brain axis, illustrating how high-inflammatory diets initiate a malignant cascade: beginning with gut dysbiosis and barrier leakage, followed by immunometabolic reprogramming of adipose tissue, and culminating in the "Trojan Horse" effect at the blood-brain barrier. This process facilitates amyloid-beta accumulation and bioenergetic crises, forming the molecular basis of T3DM. While the DII remains an irreplaceable tool for large-scale historical and cross-cultural epidemiological research, we argue that the FII represents an important methodological advancement toward precision nutrition. By quantifying intra-group heterogeneity and capturing whole-food effects, the FII is designed to address the clinical "translation bottleneck" of nutrient-based assessments. Furthermore, we explore the clinical integration of the Food Inflammation Scores of Individuals (FISI) with digital health platforms and artificial intelligence, proposing novel, pre-emptive tools such as Children's FISI (C-FISI) and Pregnancy FISI (P-FISI) for life-cycle management. This review bridges the gap between nutrition science and neuro-metabolic pathology, providing a novel theoretical framework and practical tools for the integrated management of MetS and the early prevention of T3DM.