Effects of heat-killed Lactobacillus kunkeei YB38 on human intestinal environment and bowel movement: a pilot study

It is well known that lactic acid bacteria supplementation is beneficial for intestinal conditions such as microbiota; however, the effects of killed-lactic acid bacteria on intestinal conditions are largely unclear. This study aimed to evaluate the effect of heat-killed Lactobacillus kunkeei YB38 (YB38) at a dose of approximately 10 mg/day on human intestinal environment and bowel movement. This single-blind study enrolled 29 female subjects with a low defecation frequency who consumed heat-killed YB38 at four increasing dosage levels: 0 (placebo), 2, 10, and 50 mg. Each dose was consumed daily for two weeks, with a two-week baseline period preceding the dosing-period and a two-week washout period ending the study. Observed levels of Bacteroides fragilis group significantly decreased with intake of heat-killed YB38 at ≥10 mg/day compared with levels during placebo intake (P<0.01). Faecal pH significantly decreased with 10 and 50 mg/day intake (P<0.01 and 0.05, respectively). Acetic acid levels tended to increase in faeces at the 50 mg/day dose (P<0.1). Bowel movement tended to increase in all heat-killed YB38 intake periods (P<0.1). In conclusion, heat-killed YB38 altered human intestinal microbiota at doses of ≥10 mg/day and tended to increase bowel movement at ≥2 mg/day. This is the first study to show the intestinal microbiota-altering effect of L. kunkeei and to report the bowel movement-improving effect of heat-killed lactic acid bacteria.