Saliva, as a complex and easily accessible biological fluid, contains a wide range of biochemical, hormonal, and immune components similar to those found in blood plasma. Therefore, it can serve as a non-invasive alternative to blood samples for disease diagnosis. In this narrative review, a search was conducted in databases such as PubMed, Google Scholar, Scopus, and ScienceDirect, and 79 articles published between 2015 and 2025 were examined; based on the keywords, 66 articles were selected for analysis. Recent studies have shown that salivary components—including proteins, enzymes, antibodies, hormones, metabolites, and small RNAs—can reflect physiological and pathological changes in the body. In the field of metabolic diseases, saliva has emerged as a valuable source for identifying biomarkers associated with obesity, diabetes, dyslipidemia, and non-alcoholic fatty liver disease (NAFLD). Measurement of salivary biomarkers such as insulin, leptin, adiponectin, ghrelin, and TNF-α has shown a strong correlation with their serum levels and can facilitate the early detection of insulin resistance and chronic inflammation. Moreover, salivary miRNAs, due to their regulatory role in metabolic pathways, have gained importance in distinguishing different obesity phenotypes. In diabetic patients, the concentrations of salivary glucose, fructosamine, and 1,5-anhydroglucitol are considered reliable indicators for monitoring blood glucose control. Overall, salivary diagnostics, through the use of modern molecular technologies, offers new horizons in the diagnosis, monitoring, and prediction of metabolic diseases and may serve as a foundation for developing non-invasive, accurate, and cost-effective diagnostic methods in the future of medicine.
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