Collagen is a central structural component of the extracellular matrix and, beyond its mechanicalrole, is increasingly studied as a diet-responsive modulator of tissue repair, inflammation, andmetabolic homeostasis. Concurrently, collagen supplements have become widely consumed forcosmetic outcomes (skin, hair, nails), musculoskeletal health, and, more recently, as adjuncts inlifestyle-related disorders such as obesity, diabetes, and cardiovascular disease. This reviewsynthesizes contemporary evidence on (i) collagen biology relevant to lifestyle disorders, (ii)dietary strategies that support endogenous collagen maintenance, and (iii) clinical and preclinicalfindings on collagen supplementation for metabolic, cardiovascular, dermal, joint, and gutoutcomes. A structured literature mapping approach prioritized randomized controlled trials,systematic reviews/meta-analyses, and mechanistic studies published through 2025. Overall,collagen peptides show consistent, modest benefits for skin hydration and elasticity and variablebenefits for body composition and cardiometabolic risk markers; effects on glycemic endpointsremain less consistent. Biological plausibility is supported by evidence that bioactive collagenderived peptides are absorbed and may influence extracellular matrix remodeling, immunesignaling, and gut microbiota. However, heterogeneity in collagen source (marine vsbovine/porcine), molecular weight, dosing, outcome definitions, and trial duration limitsgeneralizability. Future work should emphasize product standardization, long-term safety,comparative effectiveness versus dietary optimization, and mechanistic human studiesintegrating biomarkers and microbiome profiling.