Dietary patterns greatly affect periodontitis, a chronic inflammatory disease that compromises both dental and systemic health. According to the emerging evidence, periodontal risk is more strongly associated with the overall dietary quality, especially fiber density intake, than any one micronutrient. While the average intake in industrialized countries is only half of the recommended 30 g day⁻¹, high-fiber diets such as the Mediterranean diet, the Dietary Approaches to Stop Hypertension (DASH), and whole-food plant-based diets are consistently associated with a 20–40% lower periodontitis prevalence. Dietary fiber plays a central role in regulating immune responses, strengthening tissue barriers, improving metabolic homeostasis, and shaping a healthy microbiome through its microbial fermentation products: short-chain fatty acids (SCFAs). This makes it a biologically rational and clinical evidence-supported strategy for the prevention and management of periodontitis. Integrating high-fiber diet recommendations into routine periodontal care and public health policies could be a crucial step towards more comprehensive oral and systemic health management. This narrative review elaborates on the mechanistic, observational, and intervention data highlighting the role of dietary fiber, especially SCFAs, in periodontal health.