The role that the gut microbiome plays in aging is increasingly being appreciated in the research world as more evidence arrives to support it. A new publication reviews the various supporting evidence and takes a look at the gut microbiome in the context of poor diets and how they may facilitate the progression of dysbiosis and disease .
What is the microbiome?
The microbiome is the varied community of bacteria, archaea, eukarya, and viruses that inhabit our guts. The four bacterial phyla of Firmicutes, Bacteroidetes, Proteobacteria, and Actinobacteria comprise 98% of the intestinal microbiome.
The microbiome is a complex ecosystem whose activity regulates multiple functions of the gut and also interacts and helps to regulate our immune systems and energy metabolisms. The beneficial bacteria in our guts also help to prevent the growth of harmful bacteria, protect us from invasive microorganisms, and help to maintain the integrity of the intestinal barrier.
As we age, the diversity and numbers of beneficial bacteria tend to decline. There is a strong correlation between decreased microbiome diversity and declining health, and microbiome health has been associated with a number of metabolic conditions, such as type 2 diabetes and obesity. On the other hand, older people who maintain a more healthy gut microbiome tend to live longer and in better health.
We have talked about the role that dysbiosis, the age-related changes to the gut microbiome, plays in the loss of intestinal barrier integrity, which allows bacteria to infiltrate deeper into the body. This is likely to contribute to inflammaging, the chronic, age-related inflammation that drives disease progression and harms tissue regeneration.
Age-related gut dysbiosis is a microbial imbalance in the gut that favors a shift towards proinflammatory microbes and a decline of beneficial microbes, such as those responsible for creating butyrate (and other beneficial short-chain fatty acids), a compound vital for creating the energy that colonocytes and other gut wall cells feed on. These changes lead to chronic inflammation and impair the intestinal barrier, causing it to leak, hence the common name for the condition being “leaky gut” .
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.
Easily digestible, energy-dense, low-fiber-content foods harm the microbiome
It is known that a diet with easily digestible, energy-dense, low-fiber-content is harmful to health and leads to the formation of visceral fat, the type of fat tissue that is stored deeper than normal belly fat and that forms around your major organs, including the liver, pancreas, and kidneys. Visceral fat also contributes to chronic inflammation and hence to inflammaging, helping to speed up aging and disease progression.
It also appears to influence the gut microbiome and cause changes to the bacterial populations in the gut. The strength of this influence remains to be seen, but its effect on health via changes to the microbiome may be considerable and equally as important as physical activity for health and aging.
This adds yet more fuel to the fire, making it increasingly clear that microbiome health and exercise are the foundations of longer, healthier lives and that we should do all we can now to ensure we achieve both things as part of a personal longevity strategy.
Science is progressing rapidly, especially in the aging field, but this is no reason to be complacent. Science, especially medicine, is, by its nature, complex and can be unpredictable. We all hope that rejuvenation therapies will arrive sooner rather than later, but it is hard to predict when they will be available; this could be in a decade, or it could be longer than we think. For that reason, we should do all we can now to increase our odds of making the cut.
Exercise and balanced diets are relatively low-tech and low-cost approaches to healthy longevity, and everyone in the community should be engaging in these practices if they are serious about living long enough to benefit from the arrival of more robust rejuvenation therapies.
 Lachnit, T., Bosch, T. C., & Deines, P. (2019). Exposure of the Host-Associated Microbiome to Nutrient-Rich Conditions May Lead to Dysbiosis and Disease Development—an Evolutionary Perspective. mBio, 10(3), e00355-19.
 Cullender TC, Chassaing B, Janzon A, et al. Innate and adaptiveimmunity interact to quench microbiome flagellar motility in the gut. Cell Host Microbe 2013; 14: 571–81.