g, abdominal pain, or diarrhea. However, it is worth noting that individuals with IBS can experience positive effects by incorporating into their diet products, including vegetables and fruits, that contain water-soluble dietary fiber. Consuming dietary fiber can be challenging for individuals with IBS. According to NICE guidelines, these individuals should avoid consuming insoluble fiber (found, among others, in wheat bran). However, incorporating soluble fiber (found in plants like psyllium or oats) into their daily diet, even in the form of supplementation, may be beneficial [ 19 , 39 ]. It is worth noting that recommendations regarding dietary fiber intake are influenced by the type of IBS, as well as the type, amount, and source of fiber [ 13 ]. Insoluble dietary fiber has the ability to bind water and increase stool volume, thus stimulating intestinal peristalsis. However, existing studies indicate that this type of fiber does not contribute to the improvement of IBS symptoms and may even exacerbate symptoms in individuals with diarrhea-predominant IBS, leading to abdominal pain, diarrhea, gas, and bloating [ 39 , 40 ]. On the other hand, soluble fiber forms gels in the gastrointestinal tract, increasing stool bulk and improving its transit through the intestines [ 39 ]. It can also directly or indirectly positively influence the gut microbiota, improving its structure and function, as well as stimulating the growth of beneficial bacteria (such as Lactobacillus sp. and Bifidobacteria sp.) [ 37 , 41 ]. This type of fiber alleviates symptoms in individuals with IBS, reducing abdominal pain, bloating, and regulating bowel movements [ 13 ]. The positive effects of soluble dietary fiber can be observed in both diarrhea-predominant and constipation-predominant forms of IBS [ 13 ]. However, existing studies are insufficient to determine the recommended amount of fiber in the diet [ 42 , 43 ]. It is crucial to gradually introduce and increase the consumption of dietar Individuals suffering from IBS often associate the severity of their symptoms with the food they consume, leading them to limit the variety of foods they eat and seek information that could help them determine the appropriate selection of dietary items. Clear nutritional recommendations have not been established thus far. NICE recommends a According to the National Institute for Health and Care Excellence (NICE), basic dietary recommendations for patients with IBS should include regular meal consumption, avoiding meal skipping and large meals, drinking about 2 L (8 cups) of fluids per day (mainly water and herbal teas), limiting consumption of carbonated and alcoholic beverages, as well as reducing intake of caffeine, fats, insoluble dietary fiber (found in whole grains, cereal flakes, bran), resistant starch (present in processed and reheated foods), and gas-producing foods (including certain fruits) [ 19 , 20 ]. Additionally, the evidence for its effectiveness is of very low quality, and further research on dietary treatment for individuals with IBS is necessary [ 17 , 22 ]. Few studies are also examining the feasibility of other diets in the course of IBS. To date, gluten-free, lactose-free and high-fiber diets are of most interest, in addition to the NICE indications and the low FODMAP diet. Clinical studies conducted to date show inconclusive results regarding the effectiveness of the aforementioned diets. It is worth noting that the improvement of symptoms accompanying IBS depends on the group of people studied and additional factors that may affect nutrient tolerance. In a gluten-free diet, grain products that contain gluten are eliminated, but also other ingredients that affect the fermentation processes in the intestines and thus gastrointestinal symptoms [ 17 , 23 , 31 ]. Lactose, a milk sugar eliminated during a lactose-free diet, can also affect gastrointestinal processes [ 17 , 32 ]. On the other hand, the intake of dietary fiber, particularly water-soluble fiber, which influences the density, volume, consistency of stools and the composition and functioning of the intestinal microbiota, is increased in a high-fiber diet [ 17 ]. It may also provide benefits in terms of symptom severity and frequency. The most commonly recommended forms of physical activity among individuals with IBS include walking, cycling, swimming, yoga, or aerobics. Figure 1 The conditions for inclusion and exclusion of articles. Figure 2 General dietary recommendations for patients with IBS. nutrients-15-03662-t001_Table 1 Table 1 Products rich in specific types of FODMAP [ 21 ]. patients with IBS and lactose tolerance ( n = 53) Low lactose diet and assessment of symptoms before, during, 6 weeks after and 5 years after starting the diet Before lactose hydrogen breath tests: no significant differences in symptoms 6 weeks after starting diet: significant improvement in people with lactose malabsorption 5 years after starting the diet: significant improvement in people with lactose malabsorption Among people with IBS, it is very important to perform a lactose tolerance test and to include a lactose-free diet among those with a positive test result Netherlands, Bijkerk et al., 2009 [ 27 ] Randomized Controlled Trial, patients with IBS ( n = 275) Observation of an increase in dietary fiber of the soluble (psyllium) or insoluble (bran) fraction in the diet 12 weeks diet containing 10 g psyllium ( n = 85) vs. Low FODMAP diet During dietary intervention: relief of discomfort in both groups, with no significant difference between groups After 4 weeks of dietary intervention: 50% of those following the low FODMAP diet reported symptom relief vs. 46% of those following NICE recommendations reported symptom relief Australia, Halmos et al., 2014 [ 29 ] Single-centre, Randomized Controlled Trial, cross-over, patients with IBS ( n = 30) vs. healthy control ( n = 8) Evaluation before, during and after intervention 21 days low FODMAP diet vs.

The gut microbiota's role is crucial, affecting homeostasis and linked to FGDs through dysbiosis. Treatments include antibiotics, dietary changes, and fecal transplants. Prebiotics, including medicinal plant extracts like wild thyme (Thymus serpyllum L.), show promise. Wild thyme has traditionally treated respiratory and gastrointestinal issues and contains phenolic compounds with potential spasmolytic and antioxidant effects. Preclinical studies show wild thyme extract benefits in inflammation, IBS, and metabolic syndrome models. Recent human trials indicate improvements in gut regularity and microbiota. This study proposes wild thyme extract as a dietary supplement to benefit digestive health in FGDs, hypothesizing its immunomodulatory and prebiotic properties can reduce inflammation and restore microbiota balance. Specific objectives include analyzing microbiome impact, barrier function, inflammation, and identifying prognostic biomarkers to predict treatment response.