Microbiome-Mediated Effects of the Mediterranean Diet on Inflammation

Abstract

The Mediterranean diet pattern is increasingly associated with improved metabolic health. Two mechanisms by which consuming a Mediterranean diet pattern may contribute to improved metabolic health are modulation of the gastrointestinal (GI) microbiota and reduction of metabolic endotoxemia. Metabolic endotoxemia, defined as a 2- to 3-fold increase in circulating levels of bacterial endotoxin, has been proposed as a cause of inflammation during metabolic dysfunction. As the largest source of endotoxins in the human body, the GI microbiota represents a crucial area for research on strategies for reducing endotoxemia. Diets high in saturated fat and low in fiber contribute to metabolic endotoxemia through several mechanisms, including changes in the GI microbiome and bacterial fermentation end products, intestinal physiology and barrier function, and enterohepatic circulation of bile acids. Thus, the Mediterranean diet pattern, rich in unsaturated fats and fiber, may be one dietary strategy to reduce metabolic endotoxemia. Preclinical studies have demonstrated the differential effects of dietary saturated and unsaturated fats on the microbiota and metabolic health, but human studies are lacking. The role of dietary fiber and the GI microbiome in metabolic endotoxemia is underinvestigated. Clinical research on the effects of different types of dietary fat and fiber on the GI microbiota and GI and systemic inflammation is necessary to determine efficacious dietary strategies for reducing metabolic endotoxemia, inflammation, and subsequent metabolic disease.

Mediterranean diet intervention in overweight and obese subjects lowers plasma cholesterol and causes changes in the gut microbiome and metabolome independently of energy intake

“…Even though prior studies addressed the link between diet, gene richness and inflammation markers,7 28 56–58 intervention studies describing variation of the microbial genetic richness following an MD dietary pattern have not previously been described. Interestingly, here MD improves the inflammatory status of individuals experiencing an increase in gut microbiome gene richness during controlled energy and modified macronutrient intakes, further supporting the idea that MD might be an efficient dietary strategy to reduce inflammation 13 59…”

“…The current knowledge of the role of diet on microbiome-mediated health outcomes in humans mainly relies on observational studies in which confounding factors affect the conclusions 11. Intervention studies to address the causal effects of diet on microbiome functions are still scarce or have been performed in animal models,12 and this lack of knowledge also applies to the MD 13. Despite their cost and labour-intensiveness, randomised controlled trials (RCTs) are the gold standard for evidence-based medicine and are an appropriate tool for identifying a causal relationship of a specific nutrient or diet on a health outcome in humans 14 15…”

Gut microbiota dysbiosis in patients with hepatitis B virus–induced chronic liver disease covering chronic hepatitis, liver cirrhosis and hepatocellular carcinoma

“…In this study, a lower abundance for Firmicutes and a higher abundance for Bacteroidetes were found in CHB patients than in healthy controls; similar findings were also observed in LC and HCC groups compared with the healthy group. The potential pathogenesis might be due to the fact that most Bacteroidetes belonged to gram‐negative bacteria which were the main contributors of lipopolysaccharide (LPS) synthesis; whereas most Firmicutes were gram‐positive bacteria without LPS synthesis . Hence, the higher Bacteroidetes / Firmicutes ratio meant a higher burden of LPS exposure.…”

Role of Gut Microbiota in Neuroendocrine Regulation of Carbohydrate and Lipid Metabolism via the Microbiota-Gut-Brain-Liver Axis

“…This research demonstrated that in comparison with soy oil (high in polyunsaturated fat) diet-fed mice, coconut oil (high in saturated fat) diet-fed mice presented an increased relative abundance of Allobaculum, Anaerofustis, F16, Lactobacillus reuteri and Deltaproteobacteria, along with a decreased relative abundance of Akkermansia muciniphila in the cecum microbiota. Another study indicated that high saturated fat diet increased the ratio of gram-negative intestinal microbiota, and then increased endotoxemia [72]. Meanwhile, Mani et al investigated the effects of different dietary oil treatments on ex vivo endotoxin transport in pig ileum tissue, and they found cod liver oil and fish oil (unsaturated fat) deceased gut permeability, while coconut oil (saturated fat) increased gut permeability.…”