An article published in Food Chemistry elaborated on the health benefits of culinary herbs and spices. It stated that these plant extracts harbor the potential for prebiotic effect, owing to their polyphenol content. The bioactive constituents likely harbor anti-inflammatory properties and modulate the gut microbe. Using herbs and spices could prevent certain diseases associated with impaired gut barrier function and obesity.
Many branches of alternative medicine, like Ayurveda, Siddha, and Unani, originated in India. The use of spices and herbs for medicinal purposes is an age-old practice, used even today – owing to the anti-inflammatory and antioxidant properties of these plant extracts and their high polyphenol content.
The fresh aerial parts (leaf and flowers) of certain plants are used as culinary herbs, whereas the dried remainder parts are used as a culinary spice. In Ayurveda, herbs and spices are not only used for promoting health but also for disease prevention.
Many herbs are used for treating mild gastrointestinal disorders, for instance, ginger for indigestion, turmeric during jaundice, licorice to attenuate gastrointestinal discomfort, and mint supplements during irritable bowel syndrome (IBS). Herbs and spices are also used to ward off complications related to obesity, cardiovascular diseases, stroke, and certain cancers.
The Mediterranean diet includes many herbs and spices, which renders its anti-inflammatory and oxidative stress reduction potential. Although there are indications for using herbs and spices for medicinal purposes, thorough scientific investigation is warranted before their prescription for health benefits.
The gut microbiome comprises bacteria, viruses, and eukaryotes. The colon and the large intestine harbor approximately 3.8 x 1013 microbes; the majority are bacteria. The gut microbiota can be categorized in many ways and differs according to the host’s age, dietary pattern, health status, environment, and medication use.
Identifying and characterizing the gut microbiota can be culture-independent (for example, fluorescent in situ hybridization or FIAH) or culture-dependent (traditional method of bacterial plating). The advanced culture-dependent method also exists, like meta-genomics sequencing, polymerase chain reaction (PCR), DNA sequencing, and immunoglobulin A sequencing.
Functions of the gut microbiome have been studied using human fecal specimens and multiple-stage complex gut models to determine the effects of dietary components on the gut microbial community and the effects of the gut microbiome on the overall well-being of the host. However, the entire functionality remains incompletely understood.
This literature review explored current research findings on the effects of herbs and spices on gut microbes and the resulting health benefits.
Dietary modulation of the gut microbiota can improve overall health. Probiotics are dietary non-digestible carbohydrates that are not destroyed by the enzymes and digestive acids secreted by the upper digestive tract and enter the colon as fructans and galactans.
These metabolic byproducts are selectively utilized by beneficial bacteria which confer health benefits and improve the dysbiosis caused by illness, poor nutrition, aging, antibiotic use, and lifestyle alterations. Habitual consumption of probiotics can alter gut microbes by promoting specific bacterial populations.
Anaerobic gut bacteria ferment indigestible carbohydrates, which produce SCFAs (short-chain fatty acids). SCFAs impart numerous health benefits, such as – fat reduction, impeding type 2 diabetes mellitus (T2DM) progression, along with anticarcinogenic effects.
Another substance beneficial for health is prebiotics. Prebiotics are substrates selectively used by the host microbiome to confer health benefits. Prebiotics use several pathways leading to positive impacts on health. They promote polyphenol production; these modulate the gut microbiome.
Polyphenols are also found in herbs and spices; hence, these plant extracts may impose prebiotic effects. Polyphenols are phytochemicals; dietary polyphenols aid in maintaining gut homeostasis by selectively acting as prebiotics. They also show antipathogenic and antioxidant effects and play crucial roles in cell signaling, insulin sensitivity, and synthesizing inflammatory mediators.
About 90-95% of the dietary polyphenols reach the colon, are metabolized by gut microbes, and are transformed into metabolites that affect the bioavailability of polyphenols (and hence the health benefits).
Polyphenols can be structurally classified into flavonoids and non-flavonoids. Coumarin and tannins can also be included under dietary polyphenols. Flavonoids modulate the gut microbiome by transforming into absorbable metabolites from an unabsorbable parent. The metabolites, quantity of the consumed polyphenol, and action of gut microbes determine the health benefits. Tannins found in nuts and berries also confer health benefits by converting ellagitannins into urolithin metabolites. These two pathways cause homeostasis of the gut microbiome, prevent oxidative damage and inflammation, and confer an antimicrobial effect against invading pathogens.
However, there remain inconsistencies in herb and spice inventions. Such results can be attributed to the low bioavailability and the variable content of polyphenols in different plant derivatives. The polyphenol content also varies according to the harvesting techniques, shelf life, processing, and cooking methods.
Many studies have found that spices and herbs positively alter gut microbiota. Certain herbs also reduce the risk of cancer by acting as anti-inflammatory compounds. The anti-inflammatory effects are also pronounced in cardiovascular diseases and inflammatory bowel disease (IBD). Spices promote SCFA production, which has an anti-obesity effect. Researchers have the anti-obesity properties of ginger root. Moreover, ginger and turmeric benefit by increasing the number of beneficial gut microbes.
More studies are warranted to study the impacts of spices and herbs on the gut microbiome and their health benefits on the host before their inclusion into dietary guidelines.
Declaration of Competing Interest
The authors declared a conflict of interest, as one author works Pukka Herbs Ltd and another is in receipt of a PhD studentship funded by PUKKA Herbs Ltd.