Do synbiotics really enhance beneficial synbiotics effect on defecation symptoms in healthy adults?: Randomized, double-blind, placebo-controlled trial

GOALS: We examined whether synbiotics enhance improvement by probiotics. BACKGROUND: Probiotics, which are beneficial microbacteria, are a nutritional intervention for treatment of functional constipation or its tendency. Prebiotics, meanwhile, can promote the proliferation of probiotics in the gastrointestinal tract and enhance their beneficial effects. Synbiotics, a combination of probiotics and prebiotics, may be superior to probiotics in the treatment of defecation-related symptoms, but this requires elucidation. STUDY: This randomized, double-blind, placebo-controlled study enrolled 69 healthy adults with constipation tendency. Participants were allocated to either control, probiotics, or synbiotics groups and they recorded details of their defecations and their condition. The first 2 weeks were the observation period and the latter 2 weeks were the intervention period, in which participants took test foods. Probiotic foods included Bifidobacterium longum NT strain (10(10) CFU/day), synbiotic foods included the NT strain (10(10) CFU/day) and galactooligosaccharide (1 g/day). Placebo foods contained the vehicle only. Participants answered questionnaires (Patient Assessment on Constipation Symptoms [PAC-SYM], and one on dietary history) on the last day of each period. RESULTS: Nine participants withdrew consent, and 2 of the remaining 60 had missing data. Age, body mass index, and sex were not significantly different between the 3 groups. Frequency of bowel movements in the fourth week, the primary endpoint, was not increased in the probiotics or synbiotics groups compared with the control group, and the frequency of bowel movements and days with defecation were not changed by probiotics or synbiotics during the intervention period. Probiotics and synbiotics did not improve stool conditions, although incomplete defecation was improved by probiotics but not by synbiotics compared with placebo. PAC-SYM indicated that stool condition and total scores were improved by probiotics but not by synbiotics during the intervention compared with placebo. CONCLUSION: The probiotic strain Bifidobacterium longum NT can improve constipation symptoms, especially stool condition, but it does not increase bowel movement frequency in healthy adults with constipation tendency. Synbiotics treatment seemed to diminish this improvement of constipation induced by probiotics. This study indicates the possibility of attenuation of beneficial effects from probiotics by the use of synbiotics, contrary to synbiotics theory.