Research Blog

June 14, 2024

A Western Diet Promotes Dysbiosis…The Mediterranean Diet Promotes Health

Diet significantly influences the management and prevention of non-communicable diseases (NCDs) such as obesity, type 2 diabetes, cardiovascular diseases, and some cancers, which are linked to inflammatory disorders and changes in gut microbiota.

The Westernized diet (WD) often exacerbates these health issues by negatively impacting gut microbiota and immune function. In contrast, the Mediterranean diet (MD) is noted for its positive effects on both the immune system and gut health and is increasingly recognized as a key component in the clinical management and prevention of various diseases globally.

Microbial and eukaryotic components of the gut. As represented in the scheme, gut mucosa is a highly dynamic structure in which microorganisms and epithelial and immune cells interact continuously.
The gut microbiota is mainly composed of the Firmicutes phylum, followed by Bacteroidetes, Actinobacteria, and other bacteria that are less abundant but equally important, including Proteobacteria and the Verrucomicrobia Akkermansia muciniphilla. Immune detection and response may be assessed at the local Peyer’s patch present in the small intestine, or through mesenteric nodes, activating immune cells and accessing the gut through the bloodstream, finally promoting the release of IgA by plasmatic B cells.
Other cells may aid in the capture of microbial antigens, coordinating the immune response, including tuft cells, M cells and even intraepithelial lymphocytes. Paneth cells prominently act through the release of antimicrobial compounds.
Enterocytes and goblet cells play a key role in maintaining the intestinal barrier, whereas enteroendocrine cells produce certain products that are essential for metabolism and the individual’s health.

Eubiosis represents a healthy state of the gut microbiota where beneficial bacteria maintain a balance, suppressing harmful bacteria. This balanced microbial environment supports various crucial functions in the body, including the production of short-chain fatty acids (SCFAs) like acetate, propionate, and butyrate from the digestion of dietary fibers. These SCFAs are vital for local and systemic functions, influencing health and disease states.

Additionally, the gut microbiota plays a key role in processing nutrients such as tryptophan, synthesizing essential vitamins, degrading dietary polyphenols, detoxifying xenobiotics, and metabolizing bile acids, all of which significantly impact overall health.

The gut microbiota plays a pivotal role in the communication between the gut and the brain, shaping what is known as the microbiota–gut-brain axis. This communication is facilitated by metabolic products from the microbiota that act as messengers, affecting the brain and other systems like the cardiovascular and skeletal systems.

These interactions can promote a healthy balance within the body or contribute to inflammation and disease in states of dysbiosis. Dysbiosis, an imbalance in the gut microbiota, is linked to a range of conditions, including neurodegenerative and metabolic disorders and inflammatory and autoimmune diseases.

Interactions between gut microbiota and immune system. The different cells in the gut mucosa detect the presence of healthy gut microbiota, their products and metabolites.
Dendritic cells (DCs) may up-take antigens and present them at the Peyer’s patch or mesenteric node, leading to Th naïve differentiation. Certain bacteria, such as Alcaligenes, may be found in the Peyer’s patch that equally regulate Th fate.
Finally, some other bacteria may adhere to the epithelium, promoting the release of cytokines to modulate the immune response. These recognitions are mainly due to Toll-like receptors or Nod-like receptors, leading to inflammasome NLRP3/NLRP6 activation.
Then, in gut eubiosis, the activated cells will conduct a proper response, including increased mucine production by goblet cells, augmentation of tight junctions by enterocytes, and the secretion of antimicrobial substances by Paneth cells or IgA by B cells.
Likewise, the balance between Treg/Th17 and pro-inflammatory and anti-inflammatory cytokines is vital for the regulation of immune responses, collaborating with an adequate, non-exacerbated response but also with tolerance.
Importantly, this balance is lost under pathological conditions, and an inflammatory environment is created, contributing to the normal functioning of these cells, along with the associated gut dysbiosis.

The interaction between the immune system and the microbiome is deeply influenced by diet and human evolutionary adaptations, emphasizing that dietary effects are based on overall composition rather than specific foods or nutrients. Western malnutrition often leads to chronic inflammation and metabolic issues, while in underdeveloped countries, it results in direct immunodeficiencies due to nutritional shortages.

Diet can have precipitous effects on inflammation, intestinal pH, and the composition of gut bacteria; lifestyle elements like exercise and circadian rhythms also play significant roles.

While carbohydrates are well-studied for their impact on gut health, the roles of proteins, fats, and micronutrients, such as vitamins, are also crucial as they affect gut barrier function and immune responses.

The Mediterranean Diet (MD) is highly regarded for its health benefits, which are supported by increasing scientific evidence. It consists of a nutritious blend of fiber-rich complex carbohydrates from cereals, legumes, vegetables, and fruits, along with heart-healthy polyunsaturated fats from olive oil and nuts and a range of antioxidants like flavonoids and polyphenols.

This diet also provides a well-balanced mix of essential micronutrients that help prevent malnutrition and support immune function. Moreover, adhering to the Mediterranean Diet promotes a healthy gut microbiota, which is crucial for overall health, by increasing beneficial bacteria while reducing harmful ones.

A general overview of the main nutritional components modulating both gut microbiota and immune system.
As it is represented, the Mediterranean diet, rich in plant-based aliments, presents polyphenols, high-quality fats (MUFAs and high omega 3 PUFAs), micronutrients, such as vitamins and trace elements, and dietary fiber that, in an adequate and complete food matrix, will determine their beneficial properties in maintaining gut microbiota eubiosis and its metabolic products, along with intestinal barrier integrity and immune tolerance.
On the other side, western diets and ultra-processed foods, characterized by low levels of dietary fiber or micronutrients, present a plethora of nutritional components, including refined carbohydrates (sugar and refined grains), low-quality fats (trans fatty acids and an excessive omega 6/omega 3 ratio due to the refined oils), salt and unhealthy additives (mainly sweeteners), and finally excessive red and processed meat consumption.
Moreover, they comprise a poor food matrix that will have detrimental effects at the intestinal barrier, leading to leaky gut, gut dysbiosis and altered metabolites, further leading to a local inflammation and the presence of LPS in the bloodstream that will contribute to systemic endotoxemia and chronic inflammation.

Optimal Takeaways

Diet and NCDs: Dietary choices significantly influence the management and prevention of non-communicable diseases (NCDs) such as obesity, diabetes, cardiovascular diseases, and some cancers, which share underlying inflammatory processes and gut microbiota alterations.
Impact of Diets: The Western diet often worsens these health issues by negatively affecting gut microbiota and immune function. Conversely, the Mediterranean diet (MD) enhances both, playing a critical role in disease management and prevention worldwide.
Eubiosis and SCFAs: Eubiosis describes a healthy gut microbiota state, crucial for producing short-chain fatty acids (SCFAs) like acetate, propionate, and butyrate from dietary fibers, which are vital for systemic health.
Nutrient Processing by Gut Microbiota: The gut microbiota is essential for nutrient processing, including synthesizing vitamins, metabolizing bile acids, and converting dietary elements like tryptophan, which impact overall health.
Microbiota–Gut–Brain Axis: The gut microbiota significantly influences brain communication and other bodily systems via metabolic products, enhancing overall health or contributing to disease in dysbiotic states.
Role of Diet in Microbiome and Immune Interaction: Diet profoundly impacts the microbiome and immune system interaction, with malnutrition in various forms leading to inflammation and immunodeficiencies.
Comprehensive Benefits of the Mediterranean Diet: The MD, rich in complex carbohydrates, polyunsaturated fats, and bioactive compounds, supports a balanced micronutrient intake and promotes a healthier gut microbiota, aiding in disease prevention and health promotion.

Reference

García-Montero, Cielo et al. “Nutritional Components in Western Diet Versus Mediterranean Diet at the Gut Microbiota-Immune System Interplay. Implications for Health and Disease.” Nutrients vol. 13,2 699. 22 Feb. 2021, doi:10.3390/nu13020699 This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/)