The role of the microbiota is increasingly well known for its digestive, immune, physiological and neurological functions. This veritable internal ecosystem fascinates researchers. They are now trying to interpret the links between its instability and certain pathologies such as autoimmune and inflammatory diseases. These discoveries are on the verge of leading to new therapeutic approaches1.
The description of the human microbiota
A microbiota consists of :
- micro-organisms,
- bacteria,
- virus,
- parasites,
- mushrooms.
It contains the largest number of non-pathogenic bacteria in the human body (1013 located mainly in the small intestine and colon). Among this bacterial community, some perform crucial functions for the host.
It is precisely this symbiotic aspect that intrigues scientific research. It has been shown that the suppression of the microbiota (dysbiosis) favours the development of numerous pathologies. This bidirectional relationship acting on physiology therefore deserves to be explored further.
Diet and the role of the gut microbiota
It is now known that dysbiosis, in other words the qualitative and/or functional deterioration of the intestinal microbiota, has an impact on health. It is therefore a biomarker that can determine the development of certain diseases.
For example, increased fat maintains chronic inflammation in diabetes or obesity. These increase the proportion of inflammatory lipopolysaccharides. Thus these antigens provoke an immune response and become able to pass into the bloodstream, liver and tissues. As a result, the establishment of chronic inflammation will promote the development of insulin resistance, a prerequisite for diabetes and obesity.
The regulation of the microbiota is therefore probably involved in increasing the permeability of the intestinal walls. In addition, some bacterial metabolites could influence the development of cardiometabolic diseases such as arterial hypertension or atherosclerosis. In particular, trimethylamine, a waste product of the microbiota, is a substance known to promote the appearance of atherosclerotic plaques.
Enteral nutrition and dysbiosis
The enteral nutrition used mainly in hospitalised patients often leads (together with the drugs administered) to metabolic stress, which is responsible for a marked dysbiosis2 . This is mainly characterised by diarrhoea with multiple consequences for the patients.
However, various studies have shown that impaired intestinal function is associated with decreased faecal concentrations of short-chain fatty acids (SCFAs)3.
Diarrhoea associated with this feeding method can therefore be prevented by using a polymeric enteral formula supplemented with a fibre blend. This has the effect of increasing the production of SCFAs, which contributes to improved intestinal function.
In addition to its role in the prevention of digestive disorders, the microbiota can have a positive effect on energy intake. It therefore represents a new avenue to study in order to improve the efficiency of the fluids provided to tube-fed patients.
The brain under the influence of the gut
The nervous system that governs the intestine (enteric nervous system or ENS) contains 200 million neurons! Its primary function is to ensure intestinal motricity. However, it remains in close interaction and connection with the central nervous system (CNS). This is why it is often referred to as the second brain. The balance of the microbiota acting on the CNS can therefore influence :
- the vagus nerve and modulate brain function;
- the CNS via the bloodstream and alter certain nerve functions;
- several endocrine functions...
Moreover, intestinal dysbiosis is regularly observed in neurodevelopmental disorders or neurodegenerative diseases, such as Parkinson's or Alzheimer's.
In conclusion, we know that the gut microbiota plays an important role in digestive functions, but also in metabolic, immune and neurological functions. Consequently, this topic has a good chance of remaining central to biological and medical research.
Sources :
1 https://www.inserm.fr/dossier/microbiote-intestinal-flore-intestinale/
2 Schneider S-M. Microbiota and enteral nutrition. Gastroenterol Clin Biol 2010;34:S57-S61.
3 https://www.clinicalnutritionjournal.com/article/S0261-5614(05)00174-3/fulltext