Overlooked contributions of Ayurveda literature to the history of physiology of digestion and metabolism.

Ayurveda is a traditional system of healthcare that is native to India and has a rich documented literature of its own. Most of the historians agree that the documentation of core Ayurveda literature took place approximately in between 400 BCE and 200 CE, while acknowledging that the roots of its theoretical framework can be traced back to a much earlier period. For multiple reasons many significant contributions of Ayurveda literature to various streams of biological and medical sciences have remained under-recognized while recounting the historical milestones of development. This is true in the context of the physiology of digestion and metabolism too. In this communication we try to reconstruct a picture of the processes of digestion and metabolism as had been understood by ancient Ayurveda scholars. Though this understanding was primitive and insufficient in many ways, we argue that this deserves to be documented and acknowledged. To help with grasping the importance of these contributions, we juxtapose them with the corresponding insights pertaining to this subject reported by prominent western scientists. The major contributions of Ayurveda that have been recounted in this paper are those related to the description of three distinct phases of digestion (Avasthapaka), multiple sets of transformative entities acting at different levels of metabolism (Agni), and the roles ascribed to various internal and external factors in executing these physiological functions.