Background: A high-calorie diet results in the development of prediabetes (PD) or type 2 diabetes mellitus (T2DM). This diet has been reported to cause changes in microbial composition, concentration levels of glycemic parameters, and immune cells or inflammatory cytokines. This systematic review and meta-analysis aimed to evaluate the effects of prebiotics, as well as Mediterranean and plant-based dietary interventions, on gut microbiota composition and glucose homeostasis in individuals with PD or T2D. Methods: This systematic review and meta-analysis was developed according to the 2020 PRISMA guidelines and checklist. PubMed, EBSCOhost and Google Scholar were the three databases that were used to search for electronically published studies. Data extraction was conducted and examined by the reviewers and all the eligible studies were selected. To test for the quality and biases of the included studies, the Downs and Black checklist was used, followed by the use of Review Manager 5.4. A forest plot was used for meta-analysis and sensitivity analysis. The strength of the evidence was assessed using the Grading of Recommendation Assessment, Development and Evaluation approach. Results: Overall, eight studies met the inclusion criteria: seven focused on patients with T2D, and one focused on patients with PD. The prebiotic dietary intervention did not have a statistically significant effect on glycemic control, including fasting blood glucose (FBG) and glycated hemoglobin (HbA1c). However, one study investigating the Mediterranean diet reported a significant effect on glycemic control. Both prebiotic and Mediterranean dietary interventions were found to beneficially influence gut microbial composition in the intervention groups compared to the placebo groups. No studies assessed the impact of a plant-based diet on microbial composition and glucose parameters. Conclusions: This review indicated that dietary intervention with a prebiotic or Mediterranean diet shows to beneficially improve the gut microbiota composition of Firmicutes, Bacteroidetes and Bifidobacteria in patients with PD or T2D. However, their beneficial effects on FBG and HbA1c were less clear and uncertain due to limited reports, particularly regarding the Mediterranean dietary intervention.

Introduction Chronic consumption of a high-calorie diet compromises the gut microbiota and the integrity of the intestinal wall, which causes translocation of bacterial lipopolysaccharides (LPS) into the blood. This elicits the secretion of pro-inflammatory cytokines, resulting in inflammation. However, how a high-fat high carbohydrate diet affects intestinal permeability and its possible role in the development of prediabetes have not been investigated. This study investigated the effects of HFHC diet-induced prediabetes on gut microbiota and intestinal permeability in male Sprague Dawley rats. Methods The animals were randomly assigned into the non-prediabetic (NPD) and diet-induced prediabetic (PD) groups (n=6) for 20 weeks. Then, the fecal samples were analyzed to measure the gut microbiota level of Firmicutes, Bacteroidetes, and Proteobacteria in both animal groups. Blood glucose, plasma insulin, serum zonulin, plasma LPS, soluble CD14, tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), C-reactive protein (CRP), and intestinal fatty-acid binding protein (IFABP) concentrations were measured. Results The PD group had a reduction in the Firmicutes and an increase in Bacteroidetes and Proteobacteria levels compared to those in the NPD group. Blood glucose, insulin concentration, serum zonulin, and plasma sCD14 concentrations in the PD group increased significantly, while plasma LPS concentrations were similar to the NPD group. Concentrations of plasma TNF-α, IL-6, CRP, and IFABP, an intracellular protein expressed in the intestine, increased in PD compared to the NPD group. Conclusions the study results cumulatively suggest that chronic consumption of the HFHC diet may be associated with the dysregulation of gut microbiota, leading to increased intestinal permeability.

Given the growing global threat and rising prevalence of type 2 diabetes mellitus (T2DM), addressing this metabolic disease is imperative. T2DM is preceded by prediabetes (PD), an intermediate hyperglycaemia that goes unnoticed for years in patients. Several studies have shown that gut microbial diversity and glucose homeostasis in PD or T2DM patients are affected. Therefore, this review aims to synthesize the existing literature to elucidate the association between high-calorie diets, intestinal permeability and their correlation with PD or T2DM. Moreover, it discusses the beneficial effects of different dietary interventions on improving gut health and glucose metabolism. The primary factor contributing to complications seen in PD or T2DM patients is the chronic consumption of high-calorie diets, which alters the gut microbial composition and increases the translocation of toxic substances from the intestinal lumen into the bloodstream. This causes an increase in inflammatory response that further impairs glucose regulation. Several dietary approaches or interventions have been implemented. However, only a few are currently in use and have shown promising results in improving beneficial microbiomes and glucose metabolism. Therefore, additional well-designed studies are still necessary to thoroughly investigate whether improving gut health using other types of dietary interventions can potentially manage or reverse PD, thereby preventing the onset of T2DM.

Background A high-fat high carbohydrate (HFHC) contributes to the development of prediabetes. This condition precedes the onset of type 2 diabetes (T2D). Hence it has become a therapeutic target to prevent metabolic disorders. Several approaches such as lifestyle modifications that include moderate exercise and dietary intervention have been reported to effectively reverse prediabetes. This study investigated the effect of a low carbohydrate, high saturated fat (LCHSF) diet on glucose homeostasis and concentration levels of markers associated with a leaky gut in male Sprague Dawley rats.Methods The animals (n = 12) ingested a HFHC diet for a period of 20 weeks. After 20 weeks, the prediabetic animals were subdivided into two groups to further investigate the effects of diets for additional 12 weeks. Group 1 was the prediabetic control group (PD) that remained on a HFHC diet and group 2 was the prediabetic group that switched to a LCHSF diet (PD + DI). At the end of 32 weeks, the fecal samples were analyzed to measure the gut microbiota composition of Firmicutes, Bacteroidetes, and Proteobacteria in both animal groups. Furthermore, blood glucose, glycated haemoglobin, serum zonulin, plasma LPS, soluble CD14, tumor necrosis factor-alpha, interleukin-6, C- reactive protein, and intestinal fatty-acid binding protein concentrations were measured.Results In the PD + DI group, there was a significant increase in the Firmicutes levels and a decrease in Bacteroidetes and Proteobacteria compared to PD. Blood glucose and HbA1c concentration were significantly decreased in the PD + DI group in comparison to PD. Zonulin and sCD14 concentrations in the PD + DI group decreased compared to the PD group, while LPS concentrations were similar. A decrease in TNF-α, IL-6, CRP, and IFABP concentrations in the PD + DI group was observed compared to PD.Conclusion Taken together, these results suggest that a LCHSF diet effectively improved glucose homeostasis, gut microbiota composition and beneficially reduced the risk of insulin resistance observed in a prediabetic state.

BACKGROUND Background: The prevalence of type-2 diabetes (T2D) has increased consistently and this type of diabetes is often preceded by a condition known as prediabetes (PD). The major contributor to the progression of PD to T2D is the chronic consumption of diets high in fat and carbohydrates. However, recent reports indicate that PD can be reversed through the use of different dietary interventions composed of low carbohydrate and low fat. This systematic review aims to evaluate the beneficial effects of three diets: prebiotics, Mediterranean, and plant-based diets on gut microbiota and glucose homeostasis in patients with PD/T2D. OBJECTIVE Objectives: This review aims to provide a thorough synthesis of existing literature concerning the impact of prebiotics, Mediterranean, and plant-based dietary interventions on gut microbiota composition and glucose regulation in individuals diagnosed with prediabetes or type-2 diabetes. METHODS Methods: This review will be developed according to the 2020 PRISMA guidelines and checklist. The databases that will be used include PubMed, EBSCOhost, and Google Scholar. We will search for studies that assessed the effect of prebiotics, Mediterranean, and plant-based dietary intervention on gut composition and glycaemic indexes in prediabetic or type 2 diabetic patients. Studies will be screened by titles, abstracts, and keywords, followed by identifying the full-text articles. All studies that will pass the quality assessment will be included. Data extraction will be performed individually by three independent reviewers and discrepancies between them will be resolved by the fourth reviewer. To evaluate the risk of bias, the Downs and Black checklist will be used. If homogenous data is obtained then a meta-analysis will be conducted using a forest plot from the Review Manager software version 5.4 (RevMan). The strength of evidence will be assessed using the Grading of Recommendations Assessment, Development, and Evaluation approach (GRADE). RESULTS Results: This review will identify all the beneficial effects of prebiotics, Mediterranean, and plant-based dietary interventions on the intestinal flora and glucose homeostasis in prediabetic states and type 2 diabetes. The outcomes of this protocol will also guide future studies that can developed to further evaluate the effectiveness of these dietary interventions on other markers associated with the gut and immune function. CONCLUSIONS Conclusions: The results of this review will assess the correlation between enhancing microbial diversity and glycemic management in individuals with prediabetes and type 2 diabetes. Furthermore, these dietary interventions are anticipated to improve glucose homeostasis in prediabetes and type 2 diabetes individuals. CLINICALTRIAL Systemic Review Registration Details: This systematic review has been registered at the International Prospective Registry of Systematic Reviews (CRD42023478352).

Journal of Medical Internet Research - International Scientific Journal for Medical Research, Information and Communication on the Internet #Preprint #PeerReviewMe: Warning: This is a unreviewed preprint. Readers are warned that the document has not been peer-reviewed by expert/patient reviewers or an academic editor, may contain misleading claims, and is likely to undergo changes before final publication, if accepted, or may have been rejected/withdrawn. Readers with interest and expertise are encouraged to sign up as peer-reviewer, if the paper is within an open peer-review period. Please cite this preprint only for review purposes or for grant applications and CVs (if you are the author). Background: The prevalence of type-2 diabetes (T2D) has increased consistently and this type of diabetes is often preceded by a condition known as prediabetes (PD). The major contributor to the progression of PD to T2D is the chronic consumption of diets high in fat and carbohydrates. However, recent reports indicate that PD can be reversed through the use of different dietary interventions composed of low carbohydrate and low fat. This systematic review aims to evaluate the beneficial effects of three diets: prebiotics, Mediterranean, and plant-based diets on gut microbiota and glucose homeostasis in patients with PD/T2D Objective: This review aims to thoroughly synthesize existing literature concerning the impact of prebiotics, Mediterranean, and plant-based dietary interventions on gut microbiota composition, insulin sensitivity and glucose regulation in individuals diagnosed with prediabetes or type-2 diabetes. Methods: This review will be developed according to the 2015 PRISMA guidelines and checklist. The databases that will be used include PubMed, EBSCOhost, and Web of Science, in addition Google Scholar will be used as a search engine. We will search for studies that assessed the effect of prebiotics, Mediterranean, and plant-based dietary intervention on gut composition, glycaemic indexes and HOMA-IR values in prediabetic or type 2 diabetic patients. Studies will be screened by titles, abstracts, and keywords, followed by identifying the full-text articles. All studies that will pass the quality assessment will be included. Data extraction will be performed individually by three independent reviewers and discrepancies between them will be resolved by the fourth reviewer. To evaluate the risk of bias, the Downs and Black checklist will be used. If homogenous data is obtained then a meta-analysis will be conducted using a forest plot from the Review Manager software version 5.4 (RevMan). The strength of evidence will be assessed using the Grading of Recommendations Assessment, Development, and Evaluation approach (GRADE). Results: In this study, the pre-existing literature search in the electronic databases will be collected following the publication of this protocol. Conclusions: This review will evaluate whether these dietary interventions included in this study could be effective in reversing prediabetes or preventing the development of type 2 diabetes. In addition, the obtained findings of this review will also guide future studies that can be developed to further evaluate the effectiveness of these dietary interventions on other markers associated with a leaky gut and immune function. Clinical Trial: This systematic review has been registered at the International Prospective Registry of Systematic Reviews (CRD42023478352).