examined metabolic outcome, Everard et al. (2011) fed ob/ob mice either a control diet or a diet supplemented with oligofructose for 5 weeks. At the end of the 5 weeks, they sequenced the V1-V3 region of 16S rDNA and conducted various glucose metabolism tests. The results of the 16S rDNA analysis showed phylum-level increases in Bacteroidetes, Actinobacteria, and Proteobacteria and a decrease in Firmicutes. At the family level, they detected Bifidobacteriaceae in the prebiotic-fed group, but not in the controls. At the genus level, again they detected Bifidobacterium only in the prebiotic-fed mice. The glucose tolerance testing showed several positive metabolic outcomes associated with prebiotic consumption: lower fasting glycemia level, improved glucose tolerance, decreased fat-to-muscle mass ratio, decreased plasma triglycerides, improved gut barrier function, lower plasma lipopolysaccharide (LPS) concentrations, and reduced expression of oxidative stress and inflammatory markers.
Potential Ways to Advance the Field of Prebiotics
In addition to more research on diseased populations and on microbial metabolites, Fahey suggested several other ways to advance the field of prebiotics. First, conduct more compositional analyses of potential prebiotics. “We do too little of that,” he said. Knowing the monomeric composition, chain length, linkages, branching, side chains, and other features of the structural composition of a prebiotic can help to interpret the biological data. Second, examine prebiotic activities in natural foods, such as soybean products, beet fiber, and whole grains and their co-products. Third, continue to look beyond the bifidobacteria. Fourth, study microbiome–health index relationships, à la Hooda et al. (2012).
How can knowledge about the microbiome influence the design of healthy food, including probiotic foods? Scientists know that probiotics can impact the microbiome, both directly and indirectly, as James Versalovic described during his presentation (O’Toole and Cooney, 2008). They also know that probiotics can impact health. What they don’t know, according to Mary Ellen Sanders, is whether probiotic impacts on the microbiome are directly responsible for the observed human health benefits. Most studies that correlate microbiome changes and human health benefit do not reveal anything about causality. So the question remains, Do probiotics have a beneficial effect on health through their direct or indirect actions on the
13 This section summarizes the presentation of Mary Ellen Sanders.