Ahara (diet) is regarded in Ayurveda as one of the three sub-pillars (Trayopastambha) that sustain life, and its correct use is considered a foremost determinant of health. Viruddha Ahara, or incompatible diet, denotes foods, combinations, processing methods, quantities, or contexts of eating that are mutually antagonistic or antagonistic to the body's tissues. According to the Charaka Samhita, such incompatibility impairs Agni (digestive and metabolic fire), generates Ama (incompletely metabolised, toxic material), vitiates the Doshas, and thereby seeds a wide range of acute and chronic disorders — from skin diseases, digestive disturbance and anaemia to infertility, metabolic disease and psychological illness. This article reviews the classical framework of Viruddha Ahara: its definition, the eighteen categories described by Charaka, its proposed pathophysiology, and the disease spectrum attributed to it. It then examines these ideas against contemporary nutritional and biochemical science — including heat-induced food toxicants such as hydroxymethylfurfural (HMF), enzymatic and digestive interference, oxidative stress, advanced glycation end-products, and gut-microbiome disruption. While several classical observations align plausibly with modern mechanisms, rigorous clinical validation remains limited. The concept is best viewed as a testable, mechanistically suggestive dietary framework whose long-term health implications warrant systematic research.