Introduction: Mediterranean diet has been recommended for type 2 diabetes treatment(1). The 
impact of diet in shaping the gut microbiota is well known, particularly Mediterranean diet(2–
4). However, the link between Mediterranean diet and diabetes outcomes improvement is not 
completely clear. The aim of this clinical trial was to study the role of microbiota modulation 
by a Mediterranean diet intervention on the clinical outcomes in a diabetic population. 
Material and Methods: In this 12-week single-arm pilot study, nine participants received 
individual nutritional counselling sessions promoting Mediterranean diet. Gut microbiota was 
analysed by next-generation sequencing at baseline, 4 weeks, and 12 weeks after the 
intervention. Biochemical parameters, body composition and blood pressure were assessed at 
the same time-points (baseline, 4 weeks, and 12 weeks). Mediterranean diet adherence was 
assessed by MEDAS score at baseline and after 12 weeks. Statistical analysis was performed 
using One-way ANOVA followed by Bonferroni test for parametric variables and Friedman 
test followed by repeated Wilcoxon tests for non-parametric variables. Effect sizes (Cohen d 
test) are also presented to decide whether a clinically relevant effect is found (|d| > 0.50 indicates 
a medium effect size and |d| > 0.80 a large effect size)(5). This study was approved by the Ethics 
Committee of Administração Regional de Saúde de Lisboa e Vale do Tejo (Ref. 016/CES/ 
INV/2019) and Faculdade de Ciências Médicas|NOVA Medical School, Universidade NOVA 
de Lisboa (Ref. 55/2018/CEFCM) and was registered at clinicaltrials.gov as NCT04403217.
Results: Data are presented as mean±SD. Adherence to the Mediterranean diet (MEDAS score) 
increased from 8.11±2.26 at baseline to 10.8±1.25 after the intervention (p < 0.05; Cohen d= 
1.58). Changes in microbial richness was observed right after 4 weeks of the intervention 
(73.14±39.91 to 100±41.5, p= 0.205; Cohen d= 0.66), being negatively correlated with fasting 
glucose levels (r= -0.634; p < 0.05) and HOMA-IR (rs= -0.464; p < 0.05). On the other hand, 
HbA1c decreased from 7.53±1.07% to 6.86±0.85% (p < 0.05; Cohen d= -0.70) and HOMA-IR 
decreased from 3.79±2.98 to 2.76±2.05 at the end of study (12 weeks) (p < 0.05; Cohen d= -
0.41). Alkaline phosphatase activity was assessed in faecal samples and was negatively 
correlated with HbA1c (rs= -0.584; p < 0.05) and positively correlated with microbial diversity 
(rs= 0.608; p < 0.05).
Conclusions: This study reinforce that increasing adherence to the Mediterranean diet resulted
in a better glycaemic control in subjects with type 2 diabetes. Gut microbial richness changes seemed relevant in mediating the metabolic impact of therapeutic interventions and may 
constitute new target for the treatment of type 2 diabetes. Nonetheless, the number of 
participants that enrolled in this pilot study was small (9 participants), thus studies with a larger 
sample size are needed to confirm these findings. 

References:
1. Davies MJ, D’Alessio DA, Fradkin J, Kernan WN, Mathieu C, Mingrone G, et al. 
Management of hyperglycemia in type 2 diabetes, 2018. A consensus report by the 
American Diabetes Association (ADA) and the european association for the study of 
diabetes (EASD). Diabetes Care. 2018;41(12):2669–701. 
2. Makki K, Deehan EC, Walter J, Bäckhed F. The Impact of Dietary Fiber on Gut 
Microbiota in Host Health and Disease. Cell Host Microbe. 2018;23(6):705–15. 
3. Wolters M, Ahrens J, Romaní-Pérez M, Watkins C, Sanz Y, Benítez-Páez A, et al. 
Dietary fat, the gut microbiota, and metabolic health – A systematic review conducted 
within the MyNewGut project. Clin Nutr. 2019;38(6):2504–20. 
4. Nagpal R, Shively CA, Register TC, Craft S, Yadav H. Gut microbiome-Mediterranean 
diet interactions in improving host health. F1000Research. 2019;8(699):1–15. 
5. Aarts S, Van Den Akker M, Winkens B. The importance of effect sizes. Eur J Gen 
Pract. 2014;20(1):61–4.

Gut microbial richness as an earlier biomarker of Mediterranean diet intervention in type 2 diabetes metabolic control

The gastrointestinal tract is amongst the most densely populated ecosystems on earth, home to an abundant and diverse collection of microbial species, not just bacteria but also Archaea, viruses, fungi etc. Significant interest in this area has been sparked in recent years by an appreciation of the importance of the gut microbiota in the health of the host, and this has led to the microbiome of humans and animals being investigated in depth. Studies have drawn links between host nutrition, the gut microbiota and metabolic and immune functions, which in consequence affect physiology.



The first investigations of the structure of the microbiota were culture-based, however the introduction of sequencing technologies such as Sanger sequencing and subsequent development of 454 sequencing and metagenomics approaches have become the mainstay of microbiota studies. The creation of reference databases and analysis software has provided invaluable tools for assigning taxonomy to generated data. Great progress in characterising the structure of the microbiome recently has paved the way for ongoing and future studies on the functional interactions between the microbiota and the host. Studies on the function of the microbiota are critical in understanding the role of the microbiota in human homeostasis and disease pathogenesis.



The conference will be presenting the latest advancements in gut microbiome and health research. It will bring together experts who are driving technological advancements and striving to understand how nutrition impacts gut microbiome and the interactions between gut microbiome and health.



[https://www.nutritionsociety.org/](https://www.nutritionsociety.org/)

[@NutritionSoc](https://twitter.com/NutritionSoc)

[Member-Connect](https://membership.nutritionsociety.org/signin?message=loginRequired&next=https://membership.nutritionsociety.org)

[Cambridge Core](https://www.cambridge.org/core/societies/nutrition-society)

Recordings of the conference will be available until 13 April 2021.