Bhagavad Gita 15.14अहं वैश्वानरो भूत्वा प्राणिनां देहमाश्रितः।प्राणापानसमायुक्तः पचाम्यन्नं चतुर्विधम् ॥

The immanence of the Lord as the gastric fire in all living beings is described in this verse.Vaisvanara The fire that abides in the stomach. This fire is fanned by the bellows of the incoming and the outgoing breaths continuously and large antities of food are digested. Inside the wonderful laboratory of the stomach I digest the food by taking the form of this gastric fire.Four kinds of food (1) Food which has to be eaten by mastication (Bhakshyam). (2) That which has to be sucked in (Bhojyam). (3) That which has to be licked (Lehyam). (4) That which has to be devoured or swallowed (Choshyam). Another classification is as follows (1) Rice is PrithiviAnnam (solid food) for human beings. (2) Water is Apyannam (watery food) for birds like the Chataka. (3) Fire is Tejasannam (hot food) for certain creatures. (4) Air is Vayvannam (air as food) for serpents.अयमग्निर्वैश्वानरो योऽयमन्तः पुरुषः येनेदमन्नं पच्यते।।