Worldwide there is a high prevalence of chronic non-communicable diseases, such as obesity, type 2 diabetes, cardiovascular diseases, and certain types of cancer. Western dietary patterns characterized by a high intake of refined food products rich in carbohydrates, especially added sugars, and saturated fats, are considered, at least partially, to be responsible for the increased incidence of these chronic diseases, negatively affecting both the gut microbiota and the immune system.
On the other hand, dietary approaches such as the Mediterranean Diet have been shown to positively influence the gut microbiota and the immune system, serving as potential tools for the clinical treatment of certain diseases, as well as for the maintenance of health.
The gastrointestinal tract, in addition to absorbing nutrients, plays an important role in immune health. The gut microbiota, the largest and most diverse bacterial community in the human body that resides there, is responsible for defending our body against external agents and pathogens. While a “healthy” microbiota is still to be defined, eubiosis describes the favourable condition of the gut microbiota while dysbiosis describes the loss of balance between the “good” and “bad” bacteria. In dysbiosis, the “bad” or harmful microbiota may outnumber the “good” or beneficial bacteria.
Diet is one of the main modulators of the interaction between the microbiota and the immune system, positively or negatively impacting the gut microbiota through the promotion of specific strains of microbiota, affecting intestinal pH and the structure of the gut barrier. Modulation of the gut microbiota can affect the immune system and influence aspects related to health and disease. In eubiosis the microbiota ferment substrates and produce short chain fatty acids (SCFAs) and other by-products that can act as signalling molecules along the gut-brain axis. In dysbiosis, the gut microbiota may contribute to inflammatory conditions.
Mediterranean Diet components and immune health
The Mediterranean Diet is characterized by high consumption of fruits, vegetables, whole grains, fish, oilseeds, and olive oil. Adherence to the Mediterranean Diet can increase the consumption of nutrients such as unsaturated fatty acids, dietary fibre, polyphenols, vitamins, and other beneficial dietary components that can influence the gut microbiota. Studies have demonstrated that the Mediterranean Diet is associated with an increase in beneficial bacteria such as Bacteroidetes and Clostridium and a decrease in detrimental bacteria such as Proteobacteria and Bacillaceae. Other studies have shown that consumption of diets lower in animal protein and higher in plant protein (closer to the composition of the Mediterranean Diet) had a higher concentration of Bacteroidetes, a lower Firmicute: Bacteroidetes ratio and a higher concentration of faecal SCFAs compared to diets higher in animal protein.
The high consumption of monounsaturated fatty acids (MUFAs) and polyunsaturated fatty acids (PUFAs) in the Mediterranean Diet along with reduced intakes of saturated fats, can help regulate the composition of the microbiota, supporting the growth of bifidobacteria and lactobacillus, considered “good bacteria” while decreasing the activity or number of potential pathogens. As a result of the diet being high in fruits and vegetables, it is also rich in polyphenols which affect the gut microbiota and the immune system by increasing Lactobacillus sp. and inhibiting harmful bacteria such as Enterococcus caccae.
The Mediterranean Diet, as well as healthy eating habits that include enough foods that are sources of healthful dietary components, such as fibre, can help to modulate the composition of the intestinal microbiota. This contributes to the maintenance of the individual's intestinal, immune, and global health.
By Renata Cassar and Melissa Kaczmarczyk
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