Healthy older volunteers will be recruited to a study where they will be given four different treatments over a 28 week period. These treatments include: a prebiotic, a probiotic, a synbiotic (prebiotic + probiotic) and a placebo. Faecal samples, blood and saliva will be collected and analysed for changes in faecal microbial populations and selected immune responses.

The primary objective of this study is to determine the effect of GOS (administered at 8g/day), B. lactis BI07 (administered at 109 CFU/day) and the synbiotic (8g/day of GOS and 109 CFU/day of B. lactis BI07) on the human gut microbiota.

A double-blind, placebo-controlled, randomized crossover study will be conducted in 40 healthy older (≥60 years of age) volunteers. The placebo will consist of maltodextrin (a food grade ingredient, administered at 8g/day).

Changes in the gut microbiota will be determined by measuring bacterial population levels in human faeces using 16S rRNA targeted oligonucleotide probes and fluorescence in situ hybridisation. Faecal pH will be measured and the production of short chain fatty acids (SCFA) will be analysed and quantified using high performance liquid chromatography (HPLC).

The secondary objective of this study is to examine the effect on cellular immune function. This will be achieved by investigating phagocytosis activity, natural killer cells which are CD4+, CD8+, CD25+ and CD2+ and CD3+ subsets, the marker of T-cell maturation period., salivary IgA levels, inflammatory markers (plasma - tumour necrosis factor (TNF), IL6, IL1, chemokines and soluble adhesion molecules).

Inclusion Criteria:

• a signed consent form,
• age >60 years
• good general health
• not in the residential care.

Exclusion Criteria:

• evidence of physical or mental disease
• planned major surgery
• use of antibiotics within the previous six months