According to the biomedical clock, one says it as Circadian Cycle or Deenacharya of Ayurved principle, normal time of defecation is before sunrise. So waking up early morning and defecating the bowel, cleanses the Large intestine very easily.

Such a practice of cleaning up bowel before sunrise prevents the toxins to spread or to reverse back to the systemic absorption towards the internal organs of body. 

Subsequently avoids the recurrent illness causing due to toxins.

Thank you.