यः स्थविष्ठो धातुस्तन्मूत्रं भवति यो मध्यमस्तल्लोहितं योऽणिष्ठः स प्राणः ॥
In plain words
The grossest part of the food becomes urine, the middle part becomes blood, and the subtlest part becomes the vital breath.
Close to the Sanskrit
That which is the grossest constituent, that becomes urine; that which is the middle, that is blood; that which is the subtlest, that is prana.