"बलमारोग्यमायुश्च प्राणाश्चाग्नौ प्रतिष्ठिताः|
अन्नपानेन्धनैश्चाग्निर्ज्वलति व्येति चान्यथा ||३४२||
Strength, health, longevity and vital breath are dependent upon the power of digestion including metabolism. When supplied with fuel in the form of food and drinks, this power of digestion is sustained; it dwindles when deprived of it."
Charaka Sutra Sthana, Chapter 28, Verse 342