Lactobacilli and bifdobacteria are generally considered to be beneficial in the gut because:
• They can produce beneficial metabolites (i.e. short chain fatty acids, monosaccharides, vitamins)
• Their growth promotes acidic conditions in the colon, inhibiting harmful bacteria
• Reduced levels of bifdobacteria and/or lactobacilli are associated with certain disease states (e.g. functional gut disorders, allergy, antibiotic-associated diarrhoea)
• Positive health benefits have been observed when their numbers are restored or maintained.
Study: Increasing beneficial bacteria
Increase in lactobacilli and bifidobacteria in the gut (healthy adults) - Tuohy et al. (2007) J Appl Microbiol 102(4):1026-1032.
Method: This double-blind, placebo-controlled study at the University of Reading, involved 20 healthy volunteers who for 21 days consumed either L. casei Shirota (at least 13 x 109 CFU) as a fermented milk drink or placebo. Stool samples were collected at days 0, 7, 14, 21, and 28 to determine survival of L. casei Shirota and to determine changes to the faecal bacteria.
Results: Seven days after subjects started to take the probiotic, L. casei Shirota was recovered at a mean level of 1.1 x 107 CFU/g of faeces, and was maintained at this level over the course of probiotic feeding, but decreased after cessation of the feeding regime. Concurrently, in subjects consuming L. casei Shirota, an increase in total lactobacilli was observed, which persisted even after the regime had stopped. Bifidobacteria were also found to increase during the regime, but this increase was not sustained once consumption of L. casei Shirota had stopped.