H Yoneda, Toshihiko Tomita, Takayuki Kitano, Daisuke Morishita, Mio Kodani, Norio Nishii, Hiroo Sei, Hirotsugu Eda, Toshiyuki Sato, Mikio Kawai, Y Yokoyama, Masataka Igeta, Takuya Okugawa, Hirokazu Fukui, Shinichiro Shinzaki
INTRODUCTION: Magnesium-rich mineral water influences stool consistency and bowel habits. However, randomized controlled trials directly comparing magnesium-rich mineral water with soft water using standardized bowel outcomes remain limited. METHODS: This single-center, randomized, parallel-group trial enrolled 40 healthy subjects who did not meet Rome IV criteria for chronic constipation or irritable bowel syndrome. After a 7-day observation period, participants consumed either soft water or magnesium-rich mineral water (1 L/day) for 14 days. The primary endpoint was change in weekly mean Bristol Stool Form Scale (BSFS) score from baseline to intervention week 2, analyzed using analysis of covariance. Secondary endpoints included spontaneous bowel movements (SBM; bowel movements without rescue medication), complete spontaneous bowel movements (CSBM; SBM with a sensation of complete evacuation), subjective global improvement, time to first SBM, and daily total fluid intake. KEY RESULTS: All participants completed the trial. Compared with soft water, magnesium-rich mineral water significantly increased BSFS score at week 1 and week 2 (both p < 0.05). Weekly frequencies of SBM and CSBM were higher in the magnesium-rich mineral water group. Subjective improvement at week 2 was more frequent with magnesium-rich mineral water. Compared with the observation period, no difference in water intake was observed between the two groups. CONCLUSIONS AND INFERENCES: In healthy subjects, magnesium-rich mineral water was associated with stool softening and increased bowel movement frequency. No safety concerns were observed during the study period. These findings support further investigation of magnesium-rich mineral water as a strategy for modulating bowel habits.