Evolution of dietary preferences and the innate urge to heal: Drug discovery lessons from Ayurveda.

Highly specialized and functionally integrated cognitive systems facilitate hedonistic and healthy food preferences. Guided by survival needs, flavor preferences not only select safe, nutritious dietary components, but also those with negligible calorific value but significant health benefits, for example, spices. Feeding behavior, both innate and acquired, is guided not only by taste receptors on the tongue but also visceral organs. The gustatory cortex receives information from all senses, not just taste, suggesting multiple checkpoints in predicting and evaluating healthy foods. Ayurvedic interpretation of 'rasa' as chemistry is compatible with medicinal value of diets because, taste and odor are chemosensory perceptions. As flavor and taste are linked to the chemical structure of compounds, taste might offer clues about pharmacological activity. Ayurvedic idea of vipaka, or post digestive perception of taste, recognizes the extended role of taste receptors beyond the tongue and stretching into the viscera. Ayurvedic wisdom is consistent with evolutionary guideposts that suggest three successive stages of nutritional appraisal: before, during, and after ingesting food. While olfaction induces affinity or revulsion even before ingestion, gustatory receptors on the tongue evaluates nutritional value upon contact, and the chemoreceptors in the deeper metabolic systems probably pronounce the final verdict on the nutritive and health benefits of ingested substances. Alliesthesia, neophobia, and the extreme variation in human T2R genes (coding for bitterness receptors) illustrate the importance of adaptive learning of dietary preferences. These evolutionary clues are compatible with the Ayurvedic principle of 'rasa', in facilitating the process of drug discovery.