Expanding Our View of Herbal Medicine

This issue of JACM contains an interesting article that suggests we may need to expand the way that we think herbal medicine works. Peterson et al. show the prebiotic potential of three Ayurvedic herbs, Glycyrrhiza glabra, Ulmus rubra, and triphala (a dried fruit formulation), and suggest that the gastrointestinal benefits of these herbs may be mediated through glycan catabolic activities of the microbiome. ¹

Historically, biomedicine has taken a pharmaceutical lens to herbal medicine. Herbal medicine research and product development have been aligned with the pharmaceutical medicine model. Researchers are encouraged to identify “active compounds” and “therapeutic targets,” and to develop herbal preparations that are standardized to the known active compounds at the expense of removing the presumed “inactive” compounds.

Herbalists do not always subscribe to the pharmaceutical paradigm and emphasize that, in many cases, the whole herb is preferred to the individual constituents. However, this is a principled assertion that is supported by limited scientific evidence. Peterson et al. introduce a potential new mechanism of action for three Ayurvedic herbs. ¹

Using a clever in vitro model system, Peterson et al. demonstrate that G. glabra, U. rubra, and triphala alter the gut microbiome and may have prebiotic properties in vegetarians. ¹ They further demonstrate that each herb may influence the growth of particular species of microflora in the gut.

The scientific understanding of prebiotics continues to evolve. In 2017, a new consensus definition of prebiotics was reached by the International Scientific Association for Probiotics and Prebiotics (ISAPP). ISAPP currently proposes that prebiotics are defined as a “substrate that is selectively utilized by host microorganisms conferring a health benefit.” ² This updated definition expands the scope of foods and food constituents that can be considered as prebiotics to potentially include noncarbohydrate compounds such as plant polyphenols, sea vegetables, polyunsaturated fatty acids, and conjugated linoleic acid. Although this definition of prebiotics may continue to evolve, the current ISAPP consensus article estimates that 90%–95% of plant polyphenols, previously not considered as prebiotic because they are noncarbohydrate compounds, may be biotransformed in the small intestine by the microbiota and may, therefore, meet this definition; however, in vivo studies are required. Metabolic compounds from polyphenol biotransformation provide the host benefits in areas such as inflammation, immune function, and genomic expression.

Overall, research on polyphenolic compounds acting as prebiotics is minimal. However, researchers are starting to accumulate evidence on gut bacteria modifying effects of compounds such as polyphenols. For example, researchers have explored gut bacteria changes from polyphenols found in chestnuts, almonds and almond skins, and pistachios. ³ Similar research studies in humans have reported increased Bifidobacterium and Lactobacilli spp. with red wine polyphenols, ⁴ pomegranate extracts, ⁵ and cocoa flavonoids. ⁶ It will be interesting to see what specific foods, herbs, and spices can do to modulate microbiome communities as research expands in this area.

The human microbiome is a complex system that can be significantly and rapidly modified by changes to diet and lifestyle. Rigorous research has already established the influence of nondigestible carbohydrates on the microbiome. This study by Peterson et al. ¹ adds to a growing body of evidence that suggests that noncarbohydrate bioactive compounds found in herbal medicines may also profoundly and specifically influence gut bacteria. We can expect our understanding of how herbal medicine works continue to grow as we find new and novel research methods that move beyond the drug paradigm and allow researchers to explore complex, multitarget, and multisystem responses to traditional herbal medicine.