The gut microbial community in metabolic syndrome patients is modified by diet

Abstract

Intestinal microbiota changes may be involved in the development of metabolic syndrome (MetS), which is a multicomponent disorder frequently associated with obesity. The aim of this study was to test the effect of consuming two healthy diets: a Mediterranean diet and a low-fat high-carbohydrate diet, for 2 years in the gut microbiota of MetS patients and those in the control group. We analyzed the differences in the bacterial community structure between the groups after 2 years of dietary intervention (Mediterranean or low-fat diet) through quantitative polymerase chain reaction using primers, targeting specific bacterial taxa. We observed, at basal time, that the abundance of Bacteroides, Eubacterium and Lactobacillus genera is lower in the control group than in MetS patients, while Bacteroides fragilis group, Parabacteroides distasonis, Bacteroides thetaiotaomicron, Faecalibacterium prausnitzii, Fusobacterium nucleatum, Bifidobacterium longum, Bifidobacterium adolescentis, Ruminococcus flavefaciens subgroup and Eubacterium rectale are depleted in MetS patients (all P values <.05). Additionally, we found that long-term consumption of Mediterranean diet partially restores the population of P. distasonis, B. thetaiotaomicron, F. prausnitzii, B. adolescentis and B. longum in MetS patients (all P values <.05). Our results suggest that the Mediterranean diet could be a useful tool to restore potentially beneficial members of the gut microbiota, although the stability of these changes over time still remains to be assessed.

Introduction

The microbial communities harbored in the human intestine are involved in innate and adaptative immunity, as well as in controlling energy balance; they act collectively as an organ that is fully integrated in the host metabolism [1]. Despite mounting evidence in animal models for the role of the gut microbiota in body weight and obesity [2], [3], [4], studies in humans are scarce and causality is yet to be established. While a balanced microbiota confers benefits to the host, microbial imbalances have been associated with metabolic disorders such as dyslipidemia, insulin resistance and type 2 diabetes [5], [6]. In fact, some studies have suggested that changes in the intestinal microbiota may trigger pathogenic mechanisms that promote inflammation, insulin resistance and the development of metabolic syndrome (MetS) [7], [8]. Moreover, the loss of immunological tolerance associated with changes in the Firmicutes/Bacteroidetes ratio seems to play a significant role in the development of obesity and eventually the initiation of MetS [7].

The shaping of the gut microbiome is currently considered as a therapeutic target, since specific changes in the gut microbial community might counteract the development of obesity and MetS [9]. Although the adult human gut microbiota community is relatively stable over long periods of time [10], dietary interventions can influence its composition and could potentially be used as therapeutic tools to alleviate and treat conditions triggered by microbial imbalances [11]. In fact, it has already been shown that the consumption of a high-fat high-protein diet increases levels of Bacteroides versus Prevotella, which is more abundant after high-carbohydrate diets [12]. Moreover, the inverse relationship between Prevotella and Bacteroides has been reproduced in studies comparing the microbiota of subjects from agrarian societies with those from industrialized societies [13], [14]. In addition, the consumption of diets higher in fruit, vegetables and fiber is linked to increased microbial richness, at either the taxonomic level or the gene level [15]. The gut microbiome can even respond to short-term modifications of macronutrient content in the diet, although it quickly returns to baseline composition after the intervention ceases [16]. It is therefore hypothesized that only long-term dietary interventions can substantially impact the microbiota [11].

In this study, our aim was to evaluate the differences in the bacterial community structure of the intestinal microbiota between MetS patients and a group of individuals without MetS and to test the effect of the long-term consumption of two healthy diets: a Mediterranean diet and a low-fat high-carbohydrate diet, in restoring the gut microbiota composition.