Exercise, stress, immunity and the microbiome

Over the last 100 years humans have tended to adopt a more sedentary lifestyle, and this appears to have been accelerated with westernization. Appropriate levels of exercise are associated with multiple benefits and appear to cause positive changes in the gut microbiome[96]. Even minimal amounts of exercise have been shown to be beneficial in helping maintain physical function and avoiding falls in the frail elderly[97]. Exercise has also been associated with reduced cardiovascular disease and all-cause mortality, indicating benefits even at only one third the recommended level[98,99].
However, excessive exercise, as in the overtraining syndrome, can increase stress and cause a decrease in sleep quality and immune function[100]. Thus, care must be taken to maintain an appropriate level of exercise for maximum health benefits. At least 150 minutes of moderate-intensity exercise per week has been recommended to be beneficial for the average person and even greater benefits were found at 3 to 5 times the recommended level[99]. However, the type and amount of exercise must be tailored to the health status of the individual.
Unfortunately, many people in westernized societies do not achieve the optimal level of exercise. There may be many reasons for this, including lack of energy and motivation. These problems might be ameliorated by a diet that is less associated with inflammation. Inflammation appears to have negative effects on brain areas associated with motivation[101] and has the potential to diminish energy production by mitochondria[102]. Neuroinflammation and impaired mitochondrial function have been linked to a highly processed high-fat diet fed to mice[103]. Thus, diets such as those discussed above that emphasize whole plant foods and appear to have anti-inflammatory effects may enhance the ability and motivation to engage in adequate exercise.
Thus, overall, there is evidence that air pollution and a westernized diet and lifestyle contribute to multiple common chronic diseases and their associated elevations in inflammation. It has been suggested that both air pollution and a westernized diet contribute to dysbiotic human microbiotas, both indirectly and directly, through post-hunter-gatherer era microbes and various substances present in polluted air and a westernized diet[12]. It might be postulated that the immune reactions to these pathogenic/dysbiotic microbes may be kept to a relatively low-grade inflammation because immune system signaling only indicates the presence of a slow-growing chronic microbial colonization/infection rather than a rapidly increasing microbial threat. However, this immune system signaling could change in the context of an acute infection, as discussed further below.