In recent years, research has focused on the use of dietary fibers and prebiotics, since many of these polysaccharides can be metabolized by intestinal microbiota, leading to the production of short-chain fatty acids. The metabolites of prebiotic fermentation also show anti-inflammatory and immunomodulatory capabilities, suggesting an interesting role in the treatment of several pathological conditions. Galacto-oligosaccharide and short- and long-chain fructans (Fructo-oligosaccharides and inulin) are the most studied prebiotics, even if other dietary compounds seem to show the same features. There is an increasing interest in dietary strategies to modulate microbiota. The aim of this review is to explore the mechanisms of action of prebiotics and their effects on the principal gastro-intestinal disorders in adults, with a special focus on Galacto-oligosaccharides, Fructo-oligosaccharides, lactulose and new emerging substances which currently have evidence of prebiotics effects, such as xilooligosaccharides, soybean oligosaccharides, isomaltooligosaccharides, lactobionic acid, resistant starch and polyphenols.

Irritable Bowel Syndrome (IBS) is a chronic functional gastrointestinal disorder characterized by abdominal pain associated with defecation or a change in bowel habits. Gut microbiota, which acts as a real organ with well-defined functions, is in a mutualistic relationship with the host, harvesting additional energy and nutrients from the diet and protecting the host from pathogens; specific alterations in its composition seem to play a crucial role in IBS pathophysiology. It is well known that diet can significantly modulate the intestinal microbiota profile but it is less known how different nutritional approach effective in IBS patients, such as the low-FODMAP diet, could be responsible of intestinal microbiota changes, thus influencing the presence of gastrointestinal (GI) symptoms. The aim of this review was to explore the effects of different nutritional protocols (e.g., traditional nutritional advice, low-FODMAP diet, gluten-free diet, etc.) on IBS-D symptoms and on intestinal microbiota variations in both IBS-D patients and healthy subjects. To date, an ideal nutritional protocol does not exist for IBS-D patients but it seems crucial to consider the effect of the different nutritional approaches on the intestinal microbiota composition to better define an efficient strategy to manage this functional disorder.

Irritable bowel syndrome (IBS) is a chronic functional gastrointestinal disorder characterized by abdominal pain associated with defecation or a change in bowel habits. The pathogenesis of IBS is not completely clear, but it is known to be multifactorial and complex. Endogenous and exogenous factors such as abnormal GI motility, low-grade inflammation, increased epithelial permeability and visceral hypersensitivity, but diet and psychosocial aspects are also recognized as important actors. Furthermore, the interaction between diet and gut microbiota has gained interest as a potential contributor to the pathophysiology of IBS. To date, there is no specific diet for IBS with constipation (IBS-C); however, many studies show that fiber intake, especially soluble fiber such as inulin, could have a positive effect on symptoms. This review aims to evaluate the effects of some nutritional components such as fibers but also functional foods, prebiotics, probiotics and symbiotics on symptoms and microbiota in IBS-C subjects.

The best nutritional strategy to fight the rise in obesity remains a debated issue. The Mediterranean diet (MD) and the Very Low-Calorie Ketogenic diet (VLCKD) are effective at helping people lose body weight (BW) and fat mass (FM) while preserving fat-free mass (FFM). This study aimed to evaluate the time these two diets took to reach a loss of 5% of the initial BW and how body composition was affected. We randomized 268 subjects with obesity or overweight in two arms, MD and VLCKD, for a maximum of 3 months or until they reached 5% BW loss. This result was achieved after one month of VLCKD and 3 months of MD. Both diets were effective in terms of BW (p < 0.0001) and FM loss (p < 0.0001), but the MD reached a higher reduction in both waist circumference (p = 0.0010) and FM (p = 0.0006) and a greater increase in total body water (p = 0.0017) and FFM (p = 0.0373) than VLCKD. The population was also stratified according to gender, age, and BMI. These two nutritional protocols are both effective in improving anthropometrical parameters and body composition, but they take different time spans to reach the goal. Therefore, professionals should evaluate which is the most suitable according to each patient’s health status.

The gut microbiota plays a pivotal role in the balance between host health and obesity. The composition of the gut microbiota can be influenced by external factors, among which diet plays a key role. As the source of dietary protein is important to achieve weight loss and gut microbiota modulation, in the literature there is increasing evidence to suggest consuming more plant proteins than animal proteins. In this review, a literature search of clinical trials published until February 2023 was conducted to examine the effect of different macronutrients and dietary patterns on the gut microbiota in subjects with overweight and obesity. Several studies have shown that a higher intake of animal protein, as well as the Western diet, can lead to a decrease in beneficial gut bacteria and an increase in harmful ones typical of obesity. On the other hand, diets rich in plant proteins, such as the Mediterranean diet, lead to a significant increase in anti-inflammatory butyrate-producing bacteria, bacterial diversity and a reduction in pro-inflammatory bacteria. Therefore, since diets rich in fiber, plant protein, and an adequate amount of unsaturated fat may help to beneficially modulate the gut microbiota involved in weight loss, further studies are needed.

Inflammatory bowel diseases (IBDs) are chronic, progressive, immune-mediated diseases of the intestinal tract. The main subtypes of IBDs are Chron’s disease (CD) and ulcerative colitis (UC). The etiology is still unclear, but there are genetic, environmental and host-related factors that contribute to the development of these diseases. Recent literature has shown that dietary therapy is the cornerstone of IBD treatment in terms of management of symptoms, relapse and care of the pathology. IBD patients show that microbiota dysbiosis and diet, especially dietary fiber, can modulate its composition. These patients are more at risk of energy protein malnutrition than the general population and are deficient in micronutrients. So far, no dietary component is considered responsible for IBD and there is not a specific therapeutic diet for it. The aim of this review is to evaluate the role of dietary fibers in CD and UC and help health professionals in the nutritional management of these pathologies. Further studies are necessary to determine the appropriate amount and type of fiber to suggest in the case of IBD to ameliorate psychosocial conditions and patients’ quality of life.