Overview

• Kyushu University randomized 47 healthy adults into control, yogurt, and yogurt-plus-onsen groups for a four-week intervention.
• Participants consumed 180 g of low-sugar yogurt containing Lactobacillus bulgaricus and Streptococcus thermophilus after dinner, with the onsen group also bathing in Beppu’s chloride spring for at least 15 minutes every two days.
• Only the yogurt group showed a significant increase in gut microbiota diversity and shifts in bacterial composition relative to control.
• Both active arms reported improved defecation scores, with a larger effect in the yogurt-plus-onsen group.
• Outcomes were assessed via stool-sample microbiome surveys and a 14-item bowel questionnaire, and the authors describe the findings as preliminary due to the small sample and self-reported measures.