1958, Marion E. Faegre et al., Child Care and Training, 8th ed. Minnesota Press Archival Editions, ISBN 9780816601578, p. 99 (Google preview):
Too great emphasis on privacy in connection with the eliminative functions may, in some instances, result in a child's inability to urinate or move his bowels in an unfamiliar setting.
Three days before the fight he was eating fruit. . . . "Keeps my system regular," he said. ". . . Keeps you from getting old, moving your bowels regular."