The Compendium of Caraka 6.3.276

6.3.276

ato 'agnibalarakṣārthaṃ laṅghanādikramo hitaḥ/
saptāhena hi pacyante saptadhātugatā malāḥ//

Therefore, to protect the strength of the digestive fire, the sequence beginning with fasting is beneficial,
for the wastes residing in the seven bodily tissues are digested within seven days.