A Pilot Study on the Metabolic Impact of Mediterranean Diet in Type 2 Diabetes: Is Gut Microbiota the Key?

Abstract

The Mediterranean diet (MD) has been recommended for type 2 diabetes (T2D) treatment. The impact of diet in shaping the gut microbiota is well known, particularly for MD. However, the link between MD and diabetes outcome improvement is not completely clear. This study aims to evaluate the role of microbiota modulation by a nonpharmacological intervention in patients with T2D. In this 12-week single-arm pilot study, nine participants received individual nutritional counseling sessions promoting MD. Gut microbiota, biochemical parameters, body composition, and blood pressure were assessed at baseline, 4 weeks, and 12 weeks after the intervention. Adherence to MD [assessed by Mediterranean Diet Adherence Screener (MEDAS) score] increased after the intervention. Bacterial richness increased after 4 weeks of intervention and was negatively correlated with fasting glucose levels and Homeostatic Model Assessment for Insulin Resistance (HOMA-IR). Prevotella to Bacteroides ratio also increased after 4 weeks. In contrast, glycated haemoglobin (HbA1c) and HOMA-IR were only decreased at the end of study. Alkaline phosphatase activity was assessed in fecal samples and was negatively correlated with HbA1c and positively correlated with bacterial diversity. The results of this study reinforce that MD adherence results in a better glycemic control in subjects with T2D. Changes in gut bacterial richness caused by MD adherence may be relevant in mediating the metabolic impact of this dietary intervention.

The Effect of Dietary Interventions on Chronic Inflammatory Diseases in Relation to the Microbiome: A Systematic Review

“…Although both Roseburia and Lachnospira increased at one month, only Pseudomonas increased significantly after six months. In a 12-week uncontrolled pilot study, Ismael et al also studied a Mediterranean-based diet in T2DM patients and showed a decrease in both FBG (131.63 ± 8.53 vs. 122.50 ± 9.42 mg/dL, p = 0.581) and HbA1c (7.53 ± 1.07 vs. 6.86 ± 0.85%, p = 0.025) [ 72 ]. There was also a trend towards an increase in alpha diversity ( p = 0.47) and relative abundances of Bacteroides , Ruminococcus , Akkermansia , and Roseburia , while the relative abundance of Faecalibacterium and Prevotella decreased.…”

“…Furthermore, Pedersen et al showed significant positive associations between unclassified Enterobacteriaceae (Proteobacteria phylum) and FBG and hs-CRP ( p < 0.05) after fiber supplementation [ 73 ]. Additionally, negative correlations were found between alpha diversity (Shannon index) and B. longum with HbA1c after high-fiber dietary interventions (rs = −0.458, p < 0.05 and p < 0.01, respectively) [ 70 , 72 ].…”

“…The Mediterranean diet, a primarily plant-based dietary pattern with an emphasis on healthy fats and small portions of animal-based products, is known as a healthy dietary pattern associated with reduced risk of chronic diseases, such as CVD, and all-cause mortality [ 92 , 93 ]. In this review, Mediterranean diets were only effective at reducing clinical outcomes in patients with T2DM and had a limited or inconsistent clinical effect on patients with RA and IBD [ 56 , 64 , 65 , 70 , 71 , 72 ]. Additionally, when compared head-to-head, Candela et al showed that a vegan macrobiotic diet resulted in greater daily fiber intake (+15 g/day) and was more effective at reducing FBG and CRP than a Mediterranean diet [ 69 ].…”

Type 2 diabetes, gut microbiome, and systems biology: A novel perspective for a new era

“… 67 Table 1 summarizes studies with statistically significant differences in the composition after dietary intervention for T2D patients. 68–70 Furthermore, the differences in clinical parameters are closely related to changes at various levels of taxa (phylum, family, genus, species, and Firmicutes: Bacteroidetes relationship) ( Table 1 and Table S3).…”

Respiratory tract infections and gut microbiome modifications: A systematic review

“…However, the diversity and abundance of healthy gut microbiota can be disrupted by factors, leading to gut dysbiosis which can involve pathobiont proliferation and depletion of commensal bacteria [11]. These gut microbiota alterations have been associated with several diseases including diabetes, asthma, colorectal cancer and Parkinson's disease [12][13][14][15].…”