And again in 15th chapter, He explains as how to eat it. The energy called ‘Vaiswa:nara’ seated in the hearts of everybody digests everything that is sent into the stomach. He converts the food into energy being in the form of a variety of ‘pra:na’ and distributes it to the whole body so that every limb becomes strong, mind becomes strong and enables the intellect to guide properly.
It is because the food we eat is segregated into three categories – gross, middle and subtle. Gross form of food will be excreted in the form of waste, middle form of food forms the muscles and subtle form of food adds inspiration to the mind. The below manthra from Cha:ndogya Upanishad explains this
annam asitham thre:dha vidhi:yathe:
thasya yas stthavistto dha:thuhu that pu:risham bhavathi
yo:madhyamas than ma:msam yo: anisttaha than mahaha
Our body segregates all the food so that it gives us constant energy by which we can think, speak and act properly. When you adopt the process prescribed in Bhagavad Githa, you get sound sleep and your behavior will be perfect with the people around. Look how simple and easily understandable the message from Githa is. There is perfect scientific reasoning behind, yet the message is presented in a simple and straight forward manner for us to understand it easily.