The evolution of dietary and hygienic habits in Western countries is associated with a decrease in the bacteria that help in digestion. These very bacteria were also found in the Iceman, who lived 5300 years ago, and are still present in non-Westernized populations in various parts of the world. The depletion of the microbiome may be associated with the increased prevalence, in Western countries, of complex conditions like allergies, autoimmune and gastrointestinal diseases, obesity.

Source: Lifestyle is a threat to gut bacteria: Ötzi proves it, – ScienceDaily