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Intestinal flora - more than just digestion

Billions of bacteria and microorganisms populate the human body. Their amount exceeds that of the body cells in the intestine by tenfold, while the intestinal bacteria on their own account for around 1.5 kg of a person’s body weight.

The entirety of our microorganisms, living on and in the body, are referred to as a microbiome. This is unique for every individual and is primarily acquired during pregnancy and birth, as well as through breastfeeding and the intake of solid food. Its composition modifies over the course of a person’s life and depends on factors such as age, gender, diet and lifestyle. The relationship between a person and his bacterial flora is symbiotic in nature. In exchange for a safe habitat and regular nutrient supply, the "good" bacteria takes over a wide range of tasks. They prevent the proliferation of pathogenic germs, assist with the breakdown of indigestible food components and even produce specific vitamins.

There is increasing evidence that the microbiome could exert a far greater influence on the function and health of the body than previously believed. It is even suspected to be linked to the development of diseases such as obesity and type 2 diabetes mellitus. But how do simple unicellular organisms succeed in influencing the human body? Science offers a series of possible explanations for this.

The metabolic products of bacteria, for example, can intervene with the metabolism of their host. During the fermentation of indigestible fibers such as cellulose, one of the main constituents of plant cell walls, various short-chain fatty acids (SCFA) are produced, which exhibit a multitude of effects. First, they represent an additional source of energy for the body, particularly for the intestinal cells. While they have also been proved to have an effect on various molecular signaling pathways. However, their effect is to some extent paradoxical. For one thing, they have an anti-inflammatory effect and can positively affect the feeling of satiety, as well as energy and sugar metabolism. They can also promote the synthesis of fatty acids; while at the same time, they hinder the breakdown of triglycerides in the adipose tissue and consequently lead to their accumulation. What appears to be the most significant effect is the nature of the emerging SCFA and their concentration. Current studies reveal that higher SCFA levels in the stool are associated with obesity and other metabolic disorders. The cause of this remains unclear for the time being.

In addition, the energetic aspect also appears to play a part. Thus, it has been demonstrated in animal experiments that the intestinal flora of overweight animals functions more effectively, extracts more nutrients from the diet, and provides them to the host. Similar results have been found in obese humans. The residual energy content in their stool was lower than that of subjects with a normal weight. This indicates that by the means of the microbiome, obese humans absorb more energy from their consumed food.

The research of the Inflammation Research Excellence Cluster, a project by several German university hospitals and institutes, suggests another perspective. According to this, intestinal bacteria could be associated with inflammation in the brain. On the bases of MRI images, the researchers, led by Prof. Matthias Laudes from the University of Kiel, were able to prove the existence of inflammatory changes in the brains of obese people. Such an affected area is the hypothalamus - the brain region responsible for the control of diverse vital processes including appetite and satiety. It also became apparent that the affected subjects presented changes in their intestinal flora. These concerned a diminished number of two types of bacteria, which potentially exert an anti-inflammatory effect. Based on their work, the researchers postulated an interdependency between these two organs in the sense of a bowel-brain axis. However, whether the changes in the microbiome are the cause or the consequence of inflammation and obesity, the researchers could not reach a conclusion.

Generally, a versatile microbiome is considered healthy. Reversely, in many cases of diseases such as diabetes mellitus type 2 or obesity, a lower bacterial diversity can be documented in the intestine.

Nutrition plays a significant role in the composition of the microbiome. While a balanced and diverse diet has a positive effect on the intestinal flora, a unilateral, fat-rich and low-fiber diet causes an initially reversible shift of the bacterial species after a short time. If, however, the nutritional habits do not change over time, a lasting change is induced in the bacterial spectrum with negative consequences on health. This is confirmed by the fact that, over the last decades, the nutrition of many people has become increasingly unilateral and simultaneously the number of people affected by obesity or diabetes mellitus type 2 has grown.

Today the study of the microbiome is just beginning. Even though its importance is more and more recognized, its functioning and interdependence with the organism have not yet been adequately investigated. A profound understanding of the microbiome may, in the future, open the way for new therapies for obesity and Type 2 diabetes mellitus. But until then, one of the most important measures applicable to the health of the intestines and the body is a healthy and balanced diet.

Image 1 © “abasler” / Adobe Stock

Image 2 © “Toshihide Miyata” / Adobe Stock