Chandogya Upanishad 6.23

अन्नमशितं त्रेधा विधीयते तस्य यः स्थविष्ठो धातुस्तत्पुरीषं भवति यो मध्यमस्तन्माँसं योऽणिष्ठस्तन्मनः ॥ १ ॥

6.5.1 — annamashitam tredha vidhiyate tasya yah sthavishtho dhatustatpurisham bhavati yo madhyamastanmansam yo'nishthastanmanah || 1 ||

'The earth (food) when eaten becomes threefold; its grossest portion becomes feces, its middle portion flesh, its subtilest portion mind.

'खाया हुआ अन्न तीन प्रकार का हो जाता है — जो स्थूलतम धातु है वह पुरीष (मल) बनता है, जो मध्यम है वह मांस, और जो सूक्ष्मतम है वह मन।'