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Diseases such as inflammatory bowel diseases are increasing dramatically worldwide, but the reason for this increase remains largely unexplained. Researchers at the Christian-Albrechts-Universität zu Kiel have now investigated the cause of this problem in a study and assume on the basis of the results, that an “overfeeding” disturbs the colonization of bacteria in the intestines and is thus responsible for numerous civilization-caused diseases.

In the past, fasting due to lack of food and infections that caused diarrhea would have led the intestinal bacteria community back to their “human-specific baseline” from time to time, the researchers explain. However, these natural cleansing mechanisms have been practically eradicated in industrialized countries, which enables the continuous uncontrolled growth of bacteria. This in turn leads to an increase in bacterial products that stimulate the immune system and can ultimately trigger inflammatory reactions.

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Bacteria Are Not the Same As Bacteria

Until not so long ago, bacteria were regarded as harmful and as pathogens that had to be destroyed in order to defeat the respective diseases. However, it is now clear that certain bacteria are essential for human health. This is especially true for bacteria in the intestine. A disturbed intestinal flora – which cannot least be caused by excessive hygiene, antibiotics or a wrong diet – can lead to civilization-caused diseases such as Crohn’s disease or ulcerative colitis.

A team of researchers from the Metaorganism Specialized Research Centre of the Christian-Albrechts-Universität Kiel has now developed a further theory on the backgrounds leading to various civilization diseases. In their treatise “Exposure of the Host-Associated Microbiome to Nutrient-Rich Conditions May Lead to Dysbiosis and Disease Development-an Evolutionary Perspective”, the scientists concluded that “a constantly increasing supply of nutrients in the intestine, leads to an increased activity and altered functionality of the microbial society, which strongly disturbs the interactions between host and microbe, and leads to dysbiosis (imbalance of the intestinal flora) and disease development.”

Put simply, this means that intestinal bacteria process less of the substances that are offered to them within the framework of natural cooperation with the host. They no longer do the work they have learned in the course of evolution properly and thus promote the development of diseases.

“This overfeeding of the bacteria promotes the growth of the microbes as a whole, therefore certain bacterial species multiply to the detriment of other members of the microbiome more intensively and uncontrollably”, co-author Thomas Bosch of Wissenschaft.de is quoted. His colleague Peter Deines explains: “This way, the composition of the bacteria colonization changes the interactions between bacteria and host organism and a serious disturbance, dysbiosis, occurs.”

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The Human Stomach and Marine Habitats

In their studies, the scientists also included research results on the ecology of marine habitats, as infectious diseases have increased not only in the human population but also in the ocean over the past ten years. In doing this, they recognized some parallels to the “bacterial habitat” of the human stomach. Studies on the death of corals, oysters, fish, seaweed, algae, sponges and other invertebrates show that, in addition to urbanization and climate change, nutrient conditions in the sea can also have potentially fatal consequences.

“Changes in the environment that affect this nutrient dependence on host-associated bacteria can severely disrupt the interaction between host and microbe, leading to dysbiosis and disease development”, write Bosch, Deines, and their colleagues. If there were an unnaturally large supply of nutrients in the water, the bacteria associated with corals would be able to take advantage of this supply and no longer feed on coral metabolites. This would upset the balance of the coral microbiome and lead to diseases.

“In this connection between nutrient availability and the balance of host-bacteria relationships, we see a universal principle that goes far beyond the very specific example of corals”, explains co-author Tim Lachnit. “In studies on our model organism, the freshwater polyp Hydra, we were able to confirm this relationship experimentally.” The researchers believe that these principles observed in the ocean could also be transferred to the human microbiome.

Further Research

For future research work based on their “overfeeding hypothesis”, the scientists have set themselves the goal of finally finding new therapies. “An interesting question will be whether the original evolutionary processes that balance the microbiome also have therapeutic potential”, said Lachnit. “In future, for example, in addition to the known health-promoting effects of fasting, we will also focus on its effects on the composition and function of the microbiome and thus on the course of inflammatory diseases.”