Prebiotics are a class of nutrients that support gut microbiome integrity and function. In the gastrointestinal (GI) tract, they are fermented by gut microbes, and they help stimulate the activity of the intestinal microbiome. They also help promote the production of short-chain fatty acids (SCFAs) and the growth of certain beneficial bacteria.  

Fructo-oligosaccharides (FOS) are botanically derived molecules that are classified as prebiotics. They have been shown to help increase levels of beneficial bacteria that produce SCFAs, such as Bifidobacterium.  

Polyphenol-rich foods (such as red raspberries) have also been shown to exhibit prebiotic actions in support of GI health and the gut microbiome. An estimated 90% of dietary polyphenols are not digested in the small intestine and may therefore influence the microbiota in the colon. Polyphenols have been shown to support healthy populations of certain beneficial bacteria, such as Lactobacillus, Bifidobacterium, and other SCFA-producing microbes. Polyphenols have also been shown to support the body’s response to oxidative stress and inflammation.  

A recently published randomized, crossover clinical trial by Zhang and colleagues investigated the role of supplementation with polyphenols and prebiotics in those with prediabetes and insulin resistance (26 participants). A reference group was included in the study consisting of 10 metabolically healthy individuals. The trial consisted of two 4-week treatment periods. One period involved individuals ingesting the equivalent of 125 g of red raspberries (RRBs) per day and the other involved RRBs plus 8 g of FOS day. Data were collected based on outcomes associated with gut microbiome composition, lipid and glucose metabolism, and inflammation.  

Zhang and colleagues reported that RRB influenced the reduction of total cholesterol, low-density lipoprotein (LDL)-cholesterol, and hepatic insulin resistance. Increased levels of Eubacterium eligens and decreases in Ruminococcus gnavus were also reported in the RRB treatment period. During the RRB and FOS combined treatment period, improvements in β-cell function were observed along with increases in levels of Bifidobacterium spp. and decreases in Blautia wexlerae (B. wexlerae). Zhang and colleagues reported that populations of B. wexlerae were overabundant in individuals with insulin resistance as compared to the reference group and that the addition of FOS helped reduce levels of B. wexlerae. Of note, human research on B. wexlerate is relatively scant and contradictory; more data are required before clinical conclusions can be made.   

Prebiotics such as FOS and polyphenols may promote populations of beneficial bacteria and gut microbiome function. Although more research is needed, the article by Zhang and colleagues suggests that prebiotics may also influence metabolic health. 

By Colleen Ambrose, ND, MAT