Synbiotic consumption changes the metabolism and composition of the gut microbiota in older people and modifies inflammatory processes: a randomised, double-blind, placebo-controlled crossover study

Background
Ageing can result in major changes in the composition and metabolic activities of bacterial populations in the large gut and an impaired immune system.

Aim
To investigate the effects of synbiotic consumption on the colonic microbiota, immune function and health status in older people.

Methods
A randomised, double-blind placebo-controlled, 4-week crossover study was carried out, involving 43 older volunteers, using a synbiotic comprising the probiotic Bifidobacterium longum and an inulin-based prebiotic Synergy 1 (SudZucker, Mannheim, Germany). Faecal and blood samples were collected, and clinical status scored at the start, and at 2- and 4-week intervals, with a 4-week washout between each feeding period. Faecal bacteria were determined by fluorescent in situ hybridisation. Short-chain fatty acid concentrations, cytokine production, bowel habit and a range of clinical parameters were measured.

Results
The synbiotic increased bifidobacterial numbers by 1.4 log units (P < 0.0001) and also increased members of the phyla Actinobacteria and Firmicutes (P = 0.0004, P < 0.0001). Proteobacteria were reduced by 1.0 log units (P < 0.0001). Synbiotic feeding was associated with increased butyrate production (P = 0.0399). The pro-inflammatory response was modified by the synbiotic, with significantly reduced pro-inflammatory cytokine TNF-a in peripheral blood after 2 and 4 weeks of synbiotic consumption (P = 0.02, P = 0.0406). The synbiotic had no effect on bowel habit or any clinical parameters.

Conclusion
Short-term synbiotic use can be effective in improving the composition and metabolic activities of colonic bacterial communities and immune parameters in older people. This study was registered at clinicaltrials.gov as NCT01226212.