Why to Cleanse the Colon before the HCG Diet? Detoxifying the Colon helps maximize the release of toxins stored in hardened fecal matter. A person could lose 10 to 15 lbs of hardened fecal matter by Cleansing the COlon. Learn Why it is important to complete a Maintenance Colon cleanse before starting Phase 2 of the HCG Diet. Buy a Colon cleanse from the link above.