Science Update

Recent Randomized Controlled Trial Investigates Efficacy of Synbiotics (Prebiotics + Probiotics) on Immune Health

Our understanding of the interplay between human health and the gut microbiome continues to evolve. Newer research suggests that the combination of probiotics and the molecules that “feed” the gut microbiome (prebiotics) may play a synergistic role in support of optimal health and a normal immune response. 

A recently published randomized, controlled clinical trial (RCT) by Li and colleagues explored the potential efficacy of synbiotics on parameters related to immune health and the inflammatory response. The term synbiotics refers to the combination of probiotics and prebiotics. Prebiotics are substances that stimulate the activity of certain intestinal microbes. They are not absorbed in the gastrointestinal tract and are fermented in the gut microbiome. Examples of prebiotics include fructans such as inulin and fructooligosaccharides (FOS). FOS are botanically derived molecules that may help increase levels of beneficial bacteria in the gut microbiome, including Bifidobacterium and other microbes that produce short-chain fatty acids (SCFAs). 

This eight-week RCT involved 106 healthy adults who either received placebo or a daily combination of 500 mg FOS alongside 150 million CFU Bifidobacterium lactis HN019 and 75 million CFU Lactobacillus rhamnosus HN001. Lactobacillus rhamnosus and Bifidobacterium lactis help support gastrointestinal function, immune health, a healthy inflammatory response, cognitive health, and many other body systems

When compared to placebo, the treatment group was reported to experience greater reductions in C-reactive protein (CRP), a marker generally associated with inflammation. The authors note that CRP in the treatment group continued to decline as the study proceeded. At the study terminus, plasma interferon-ɣ declined by 19% in the treatment group, which was statistically significant when compared with placebo. The treatment group also experienced greater statistically significant increases in interleukin (IL)-10, an anti-inflammatory cytokine commonly associated with helping to promote immune system homeostasis. Increases in microbes commonly associated with a healthy gut microbiome were also observed, including those from the Lactobacillus and Bifidobacterium genera. Clostridium sensu stricto 1 and certain Collinsella species have been observed to produce SCFAs; these populations were also increased in the treatment group. Reductions in certain microbes typically associated with pro-inflammatory states such as Parabacteroides were reduced when compared with baseline. 

The study also measured the Prevotella-to-Bacteroides (P/B) ratio. A higher P/B ratio has been associated with altered insulin homeostasis and changes in IL-6 concentrations. Statistical analysis suggests that the individuals with a higher P/B ratio experienced greater effects from the synbiotic supplement; however, more research is needed before clinical conclusions can be made. In addition, the P/B ratio is itself not currently a comprehensive measure of health. Within the complex microenvironment related to the gut microbiome, the signaling pathways, microbial metabolites, and population sequencing may provide a more comprehensive snapshot of biochemical activity. 

The study’s strengths include a clearly defined primary outcome, an appropriate choice of biometrics, and a well-developed hypothesis. Study drawbacks include demographic homogeneity and a relatively short study duration. Despite the drawbacks, this study indicates that further research into the efficacy of synbiotics is merited. Future research should include an additional treatment arm that only administers probiotics to further elucidate the potential efficacy of synbiotics.

Evidence suggests that synbiotics may help support the function of the gut microbiome. Dietary sources of prebiotics include onions, garlic, leeks, soybeans, chicory root, dandelion greens, green bananas, and Jerusalem artichokes. 

By Dr. C. Ambrose, ND, MAT