A new study published recently in BMC Microbiology shows that both aging and dietary fat intake both can change the delicate balance of bacteria in the gut for the worse.
The gut microbiome
The microbiome describes the varied community of bacteria, archaea, eukarya, and viruses that inhabit our gut. The four bacterial phyla of Firmicutes, Bacteroidetes, Proteobacteria, and Actinobacteria comprise 98% of the intestinal microbiome.
The microbiome is a complex ecosystem that regulates various aspects of gut function along with the immune system, the nutrient supply, and metabolism. It also helps to control the growth of pathogenic bacteria, protects from invasive microorganisms, and maintains the intestinal barrier. Essentially, the microbiome exists in a delicate balance, and if that balance is disturbed, it can lead to a decline of health and the development of disease.
As we age, the composition and diversity of the microbiome changes, as the beneficial bacteria populations tend to decline and populations of harmful bacteria typically increase in numbers. One emerging hypothesis is that these changes to the gut microbiome lead to detrimental changes elsewhere in the body and could potentially be the origin point of inflammaging, the chronic low-grade smoldering background of inflammation typically observed in older people.
Dietary fat and aging change the microbiome for the worst
The results of the new study show how age and dietary fat intake have very powerful influences over the microbiome and can cause significant changes to occur . The researchers studied these changes in C57BL/6 (Black 6) mice, the most commonly used lab mice in the world. This particular strain of mouse is really an ideal rodent model for studying aging, as it ages in much the same way we do – which can help translate research to us.
The researchers demonstrated that diet plays a key role in the composition of the gut microbiome and that changes to diet can cause very rapid alterations to the populations of gut bacteria.
In mice fed a 45% high-fat diet (HFD) for a 10-20 period, they observed an increase of Actinobacteria (mostly of the Bifidobacterium genus). Previous studies have shown that Actinobacteria levels are typically higher in obese individuals and that the microbial population is generally less diverse in these obese individuals . In addition to this, an HFD was closely linked with body weight and the presence of proinflammatory cytokines, chemical signals secreted by cells; TNF-a, IL-1ß, and IL-6 were all elevated in these cases.
Aging was seen to increase the numbers of the Firmicutes present in the microbiome as did the presence of pro-inflammatory cytokines, which is provoked by an HFD as well as many other potential sources. The Firmicutes Clostridia and Ruminococcaceae in particular were influenced by both aging and diet.
The phylum Bacteroidetes, the family Bacteroidaceae, and the genus Bacteroides were all observed to decrease during the aging process, and, as their numbers declined, the level of proinflammatory cytokines in the colon began to rise.
More than half of the adult population worldwide is overweight or obese, while excess adiposity has been linked to chronic low-grade inflammation, contributing to the development of chronic diseases. Recent studies have showed that diet-induced alterations to the gut microbiota composition play a pivotal role in the development of obesity. However, the cause-effect relationship between obesity and gut microbiota composition is not yet fully understood. In this study, we investigated the short-term responses of gut microbiota composition to diets with different fat contents and their associations with inflammatory biomarkers.
Both aging and a high-fat diet both appear to cause significant changes to the microbiome; it could be said that a high-fat diet is almost accelerating aspects of microbiome aging as well as contributing to systemic inflammation, which is a known driver of aging. This study suggests that diet can have a significant influence on gut microbiome health and balance, and, if not maintained, it may contribute towards speeding up certain aspects of aging. While this study is in mice it certainly raises the distinct possibility that similar changes may occur in humans.
 Kim, S. J., Kim, S. E., Kim, A. R., Kang, S., Park, M. Y., & Sung, M. K. (2019). Dietary fat intake and age modulate the composition of the gut microbiota and colonic inflammation in C57BL/6J mice. BMC microbiology, 19(1), 193.
 Clarke, S. F., Murphy, E. F., Nilaweera, K., Ross, P. R., Shanahan, F., O’Toole, P. W., & Cotter, P. D. (2012). The gut microbiota and its relationship to diet and obesity: new insights. Gut microbes, 3(3), 186-202.