## 1 Introduction  
Dietary components and eating patterns can affect important health outcomes. Evidence points to a close link between dietary pattern and decreased mortality [1]. Specific factors that can influence the choices include personal preference, gender, social and cultural aspects, as well as economic considerations. As underscored by several meta-analyses and societies, including the WHO [2], the American Institute for Cancer Research [3], and the US Department of Agriculture [4], a high-quality and healthy diet rely on the limited consumption of saturated and industrial trans fats, red and processed meats, sugar, sodium, and alcohol. By contrast, the consumption of fruits, vegetables, legumes, nuts, and whole grains is greatly encouraged. The Mediterranean diet (MD) mirrors several of the above-mentioned beneficial features, since it is based on the consumption of vegetables,fruits, nuts, olive oil, and many herbs. Besides the richness of MD in essential nutrients, vegetables and herbs contain a high amount of polyphenols [5]. Polyphenols are a diverse group of naturally occurring compounds linked to various health-promoting effects. The gut-polyphenols interaction occurs after the ingestion of food, where polyphenols are modified by digestive enzymes [6]. Small amounts of polyphenols are absorbed in the small intestine, while the greatest amount remains unabsorbed and accumulates in the colon, where it is extensively metabolized by gut microbiota prior to reaching the circulation [7; 8; 9]. Information about polyphenol biotransformation, bioavailability, and in vivo physiological effects is still yet to be delineated. Since the gut microbiota play a pivotal role in host homeostasis and energy balance, changes in their composition can be associated with disease states through the promotion of immune-mediated inflammatory disorders and increasing the intestinal permeability, ultimately leading to the impairment of intestinal barrier function. Evidence from preclinical and clinical studies suggests that polyphenols or polyphenol-rich food can positively influence gut health by promoting the growth of beneficial gut bacteria and suppressing the growth of harmful bacteria. This can contribute to a balanced gut microbiome and gut barrier [7]. Za'atar is one of the most popular plant-based foods in the Eastern Mediterranean region. Za'atar is a mixture of different thym-like plant leaves including _Origanum spiroatum_ and _Thymbra Spicata_, fruits of _Rhus coriaria_ (Sumac), and sesame seeds [10]. The mixture contains hundreds of antioxidant compounds, especially polyphenols. Za'atar compounds have been studied from a gastrointestinal perspective, concerning both gut microbiota and gastrointestinal diseases, suggesting that Za'atar polyphenols may provide beneficial effects in the complex interplay between the diet, GM, and intestinal permeability [11]. In Lebanon, _Thymbra spicata_ is widely diffused. It belongs to the _Lamiaceae_ family and it is rich in polyphenols such as rosmarinic acid, carvacrol (CVL) and different flavonoids [10]. _T. spicata_ leaves and flowers are used as food ingredients in salad and in tea infusions. Different biological and bio-functional effects have been reported for _T. spicata_ including anti-oxidant and antisteatotic [12], antihypercholesterolaemia [13; 14], antitumoral [15], antiviral [16], and antimicrobial [17; 18; 19] activities. CVL is a monoterenoid phenolic compound found in the essential oils of various plants, particularly in the _Lamiaceae_ family. _T. spicata_ contains up to 80% CVL in its essential oil [20]. CVL has gained attention among the scientific community due to its diverse biological activities and its potential health benefits [21; 22; 23]. CVL exerts antimicrobial [24], antioxidant [25], anti-inflammatory [26], and antisteatotic effects [27], and is being explored for various pharmacological and nutraceutical applications. To our knowledge, no studies have reported the effects of _T. spicata_ on the gastrointestinal tract.