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Background: Ayurveda regards Agni, the digestive and metabolic fire, as the basis of health, and holds that impaired Agni produces Ama, a toxic residue that underlies many diseases. Classical texts also state that grief, fear, anger and worry impair digestion even of wholesome food. Modern research on the microbiota–gut–brain axis has shown two-way communication between the gut, its microbial community and the brain, with links to stress, anxiety and depression. Objective: To compare the Ayurvedic concepts of Agni, Ama and the mind–digestion relationship with current evidence on the gut–brain axis, and to identify research opportunities. Methods: Narrative review of classical texts on Agni, Ama and Grahani, and of selected experimental, clinical and review literature on the microbiota–gut–brain axis, Prakriti-related microbiome differences and Ayurvedic herbs with prebiotic activity. Results: Classical texts describe a bidirectional relationship: mental disturbances impair Agni, and impaired Agni with Ama formation disturbs the mind. Modern studies show that gut microbes influence stress responses, serotonin synthesis and behaviour in animals; that depression-associated microbiota can transfer depressive-like behaviour to rodents; that specific bacterial taxa are associated with depression and quality of life in humans; and that probiotics have small but significant effects on depressive symptoms. Gut microbial signatures differ between Prakriti types, and Triphala shows prebiotic activity in vitro. Conclusion: Agni and the gut–brain axis describe overlapping phenomena. Agni assessment could serve as a clinical entry point for gut-directed approaches to mental health, but requires standardised measurement and testing against microbiome and psychiatric outcomes.

Keywords: Agni; Ama; gut–brain axis; microbiome; depression; anxiety; Triphala; Prakriti