Nutrient rich diets are harmful, even if only considering the accumulation of visceral fat tissue that results from eating more calories than are strictly necessary for sustained periods of time. Visceral fat tissue produces chronic inflammation, and that in turn accelerates progression of all of the common age-related conditions. High nutrient diets also have an effect on gut bacteria, however, and it is becoming apparent that the state of these bacterial populations has a noteworthy influence on the course of long-term health. This may be as large an effect as that of exercise, but this remains to be determined in certainty.
Together with our microbes, we form a synergist relation, which is termed holobiont or metaorganism. Disturbance of this host-microbe homeostasis can lead to dysbiosis (microbial imbalance on or inside the host) and/or disease development. It is well documented that inflammatory diseases are accompanied by changes in microbial density or microbial community composition. However, comprehensive sequencing approaches have not yet led to the identification of a key pathogen, nor to the discovery of a specific pathobiome that is responsible for the disease. On the contrary, it is becoming more and more apparent that our associated microbiota is not as specific as we thought and that, even within the same individual, microbial community composition underlies strong temporal variability.
Inflammatory diseases, such as inflammatory bowel diseases, are dramatically increasing worldwide, but an understanding of the underlying factors is lacking. We here present an ecoevolutionary perspective on the emergence of inflammatory diseases. We propose that adaptation has led to fine-tuned host-microbe interactions, which are maintained by secreted host metabolites nourishing the associated microbes.
A constant elevation of nutrients in the gut environment leads to an increased activity and changed functionality of the microbiota, thus severely disturbing host-microbe interactions and leading to dysbiosis and disease development. In the past, starvation and pathogen infections, causing diarrhea, were common incidences that reset the gut bacterial community to its "human-specific-baseline." However, these natural clearing mechanisms have been virtually eradicated in developed countries, allowing a constant uncontrolled growth of bacteria. This leads to an increase of bacterial products that stimulate the immune system and ultimately might initiate inflammatory reactions.