Complex sentence: Oral intake of "L. reuteri" has been shown to effectively colonize the intestines of healthy people; colonization begins within days of ingestion, although levels drop months later if intake is stopped.
Split into simpler sentences: Oral intake of "L. reuteri" has been shown to effectively colonize the intestines of healthy individuals. Colonization begins within days of ingestion, although levels drop months later if intake is stopped.