Although it has long been known that the human intestine contains an astronomical number of intestinal bacteria, the functions of these microorganisms in human health never cease to bring pleasant surprises. Indeed, several discoveries have recently contributed to significantly improve our understanding of the enormous influence that these “friendly” bacteria have on our health.
The bacteria that make up the intestinal flora have the ability to degrade dietary fiber through the fermentation process, producing several health-beneficial nutrients in parallel (vitamins B9 and K, short-chain fatty acids). Recent discoveries indicate, however, that this digestive function represents only one facet of the many roles played by these “friendly” bacteria in the body. We know, for example, that the presence of intestinal bacteria is absolutely essential for the development and maintenance of the immune system against pathogenic bacteria or viruses.
From gut to brain
More recently, researchers made the astonishing discovery that the action of bacteria in the intestinal flora was not limited to the digestive system, but could also influence the brain. Indeed, the researchers observed that the composition of the intestinal flora exerted an impact on the levels of certain cerebral neurotransmitters and could modulate certain behaviors, such as anxiety, stress and depression. It therefore seems that the composition of the intestinal flora plays a leading role in maintaining good health, both physical and mental.
Diet influences the quality of intestinal bacteria
Another study suggests that this composition of the intestinal flora is closely modulated by the nature of the diet. For example, people who eat food typical of Western countries, that is to say rich in animal proteins and fats, have a flora composed mainly of bacteria of the Bacteroides genus. In people whose diet consists mainly of plants rich in plant fiber, this flora contains mainly the genus Prevotella.
Since the Western diet is associated with an increased incidence of several chronic diseases, these observations suggest that these differences in the composition of the intestinal flora could play an important role in the development of these diseases. The positive impact of a diet rich in plants would therefore not only be due to a direct effect of phytochemicals, vitamins and minerals on physiological functions, but also on the establishment of an intestinal flora with beneficial effects. We are what we eat, even when it comes to the bacteria that live in our gut!
Diet rich in probiotics promotes good bacteria
Under normal conditions, the composition of the intestinal flora is very stable and its modification requires long-term changes in dietary habits. A recent study, however, suggests that it is possible to modify the activity of this flora using fermented products rich in “friendly” bacteria called probiotics. The researchers observed that the regular consumption of a product containing several strains of probiotics (bifidobacteria, lactobacilli, lactococci) did not significantly modify the composition of the flora, but nevertheless caused a notable increase in the degradation of xylooligosaccharides, a class of carbohydrates very common in plants.
This effect is interesting, because other studies have shown that this degradation of xylooligosaccharides is associated with protection of the intestinal mucosa and a reduction in the development of colon cancer. Regular consumption of products containing probiotics is therefore a simple way to improve the “efficiency” of intestinal bacteria and at the same time allow them to positively influence the proper functioning of the body.
Well done JA et al. Ingestion of Lactobacillus strain regulates emotional behavior and central GABA receptor expression in a mouse via the vagus nerve. Proc Natl Acad Sci USA, 108:16050-55.
Wu GD et al. Linking long-term dietary patterns with gut microbial enterotypes. Science;334:105-18.
McNulty NP et al. The impact of a consortium of fermented milk strains on the gut microbiome of gnotobiotic mice and monozygotic twins. Science Transl Med;3:106ra106.
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