Traditional herbalism proposes numerous beneficial actions supporting digestive health, and modern research has identified many of the active constituents responsible. Mucilage acts as a demulcent, volatile oils have a carminative effect, bitters stimulate digestive secretion, even plant fiber can act as a bulk laxative, as in the case of psyllium husk. But only recently have active constituents been identified that act by favorably influencing the microbiome. Inulin, a soluble fiber found in traditional digestive herbs like chicory, is probably the most well-known and acts as a prebiotic favoring the growth of Bifidobacter and Lactobacillus, important strains with diverse beneficial effects on gut and immune health.
Recent research suggests that some botanical constituents may even have dual roles, acting both to support the human body directly and to provide fermentable substrate for the growth of beneficial probiotic strains, thus providing a synergistic action with probiotic supplements. One such class of active constituents is tannins, found in many of the barks and leaves used by ancient herbalists to support the gut, long before there was any notion of the microbiome. The value of tannins has been eclipsed and largely forgotten by modern approaches to herbalism, which tend to focus more the antimicrobial and trophorestorative properties of plants when it comes to the digestive tract, but a better understanding of the microbiome and its immunoregulatory function is beginning to redeem the wisdom of using tannin-rich herbs for intestinal health.
Classical herbalism assigned a fairly simple mechanism of action to tannins: drying or lessening secretions and tightening or tonifying loose tissues. Organoleptically, this drying and contracting action was ascribed to the astringent property of certain herbs, in which tannins play a primary role. Astringency, referring to this peculiar drying and tightening sensation, can be readily appreciated on the tongue and is characteristic of many popular beverages, including red wine, black tea, and cranberry juice.
In classical models of herbalism deriving from Galen, disease symptoms are ascribed to imbalanced tissue states and the therapeutic properties of herbs often explained by their counter effects upon tissue states, for instance warming or cooling, drying or moistening, relaxing or tonifying. In these models, excess mucus secretion was supposed to result from an excess of moisture and laxity, as if the tissues involved become so loosened that their normal secretions become excessive. Certain herbs were believed to check these secretions by drying or tightening the tissues involved, effectively relieving the symptoms, whether they involve the sinuses and nasal mucosa or the gastrointestinal mucosa. The astringent property of goldenseal, for instance, is believed to explain why that herb can support both the stomach and sinuses in this model of herbalism, while more modern approaches to herbalism would tend to explain this through its antimicrobial properties, focusing on its active constituent berberine.
Although it seems outdated, there is some physiological basis to the idea that tightening tissues can reduce excess secretion. One organ where this is definitely the case is the uterus, which relies on its own smooth muscle contractions to staunch the menstrual flow. By a mechanism similar to applying a tourniquet, blood loss from shedding the endometrium is held in check by the uterine muscle constricting blood vessels. If this tissue becomes lax for whatever reason, say reduced innervation due to a spinal restriction in the T10-L1 area, the result can be an excessive menstrual flow. Most of the herbs that were traditionally used to support menstruation, like shepherd’s purse and the unicorn roots (both Aletris and Helonias) are remarkably astringent, with an affinity for the pelvic organs. Hence, their organoleptic properties lend credence to the notion that astringents work by this effect.
Before the germ theory of disease took hold, diarrhea was likewise treated as an excessive secretion of the intestinal mucosa due to some presumed combination of dampness and laxity in the tissues. Most of the herbs traditionally recommended to treat diarrhea from any cause were astringents, and typically rich in a specific class of polyphenols called tannins. This name derives from the Latin word for oak bark, this being a rich source of tannins used historically for a different form of curing: turning animal hides into leather. Hence “tanning a hide” involved soaking it with oak bark, and it becomes easy to draw an analogy between a tough, dry piece of leather and an excessive mucus secretion being checked by the drying, tonifying action of tannins. The analogy can be stretched even further, however, by considering the crucial role of tannins in preserving the hides from microbial decomposition. Tannins make animal hides resistant to decay by saturating the cellular structure of the skin and altering hydrogen bonding between collagen fibers, essentially forming a protective barrier that proves resistant to normal microbial decomposition. While it is unlikely that this mechanism applies similarly to living intestinal epithelium, it remains true that tannin-rich herbs have been used traditionally to support the intestinal immune system. The true mechanism may involve immune modulation by triggering beneficial changes to the gut microbiome.
There is recent research to support the idea that tannin-rich herbal blends can be used synergistically with probiotics to support the gut microbiome in ways that may benefit immunity. It has been suggested that tannins can serve as prebiotics, promoting the growth of specific bacterial strains associated with short-chain fatty acid production and immune regulation. We know that a significant portion of the body’s immune system resides in the gut, and that influencing the microbiome is a powerful way to stimulate and improve immune function. This is where the old analogies involving tissue states start to break down, however useful they may be to conceptualize the healing mechanism of herbs, and start to align with a more modern understanding of human physiology. It is less likely that tannins are truly “tanning” the intestines, drying up watery diarrhea and armoring the tissue against bacterial infection, and more likely that they are signaling the immune system either directly or through their fermentation by specific probiotic strains.
The problem with the tissue-state theory is that by reducing the healing action of herbs to some property like their astringency, it implies that anything astringent should be equally effective. Astringent herbs with known effects on the intestines like cranesbill, white oak bark, silverweed, and blackberry leaf could, in theory, be replaced with tea and red wine, whereas it is obvious that not everything that may be classified as astringent has equivalent healing properties. While an astringent taste can indeed provide a clue to a given herb’s therapeutic potential, it is far more useful and scientific to consider its specific profile of active constituents.
Tannins are not the only polyphenolic compounds that provide an astringent taste, but they are considered the most important for immunity and gut health. Two specific tannins of special relevance are gallic acid and ellagic acid, which have both been studied and demonstrated to support the gut through specific mechanisms more elaborate than simply “tonifying” lax tissues. Ellagic acid can enhance intestinal barrier function and gallic acid can protect intestinal cells by increasing their antioxidant defenses, thus these two compounds act synergistically to support the intestinal lining. Both compounds also exert beneficial effects on the intestinal microbiome, making them useful to combine with probiotics as part of a holistic protocol.
Many herbs can provide relevant doses of gallic and ellagic acid; for instance cranesbill (Geranium maculatum) is an excellent source of gallic acid and was celebrated by the Eclectic herbalists for its action on the intestines. Blackberry leaf (Rubus fruticosus), another herb with similar traditional uses, is richer in ellagic acid and many intestinal astringents contain some of both within an individual profile of beneficial constituents, such as white oak bark (Quercus alba). Each of these herbs was once understood to tonify a damp, lax intestinal mucosa through its astringent properties, and while it may be a simplification, this traditional mechanism remains shockingly relevant in light of the proven effects of their active constituents. Each of these herbs is also featured in Energique® Intesticom™*, our most concentrated herbal product to date. Paired with a probiotic like our High Delivery Acidophilus, it can provide synergistic support for the intestines, immune system, and gut microbiome.
*These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease.
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