We possess a very large and diverse set of bacteria inside our bodies, and they play a vital role in process such as digestion. In effect they are the first link in the chain that leads from diet to metabolism to the pace of aging: a large portion of how environment influences natural variations in life expectancy. Researchers are still only in the very early stages of gaining a complete picture of human aging in terms of metabolism, genes, gene expression, and cellular mechanisms. It is enormously complex, but very little of this ongoing work has anything to do with our symbiotic bacteria - so by comparison next to nothing is known about how the intestinal microbiome fits into the big picture, and not much of a grasp on how important it might be in aging.
(As an aside: as soon as the research community can develop medical technologies like those envisaged in the Strategies for Engineered Negligible Senescence (SENS), natural aging and ways to influence it become a quaint old-time sideshow. We will be able to reverse the progression of aging, so why bother with those small details? To my mind that means we should all treat these discussions like a quaint old-time sideshow today, and focus more on how to make SENS happen faster).
But back to the plot: think about calorie restriction and the degree to which it (a) affects health and longevity, and (b) seems to hinge on levels of certain essential amino acids transported to cells. In that context, it seems likely that changes or differences in gut microbe populations - some of which are preprocessing your dietary intake - could have some influence. But again, there isn't much to go on in terms of solid data in comparison to research aimed at figuring out our own cells. You might look at these posts from the archives as a starting point:
- Investigating Intestinal Bacteria and Aging in Nematodes
- Becoming Aware of the Influence of Bacteria Upon Aging and Longevity
- Aging and Bacteria in the Body
- Intestinal Bacteria and Ageing
My attention was caught today by a post on changes in our gut microbiome over the past century - they have been very large indeed, now matter which causative mechanism you think might be the likely culprit:
[Researchers] analyzed microbiome data from ancient human fecal samples collected from three different archaeological sites in the Americas, each dating to over 1000 years ago. In addition, the team provided a new analysis of published data from two samples that reflect rare and extraordinary preservation: Otzi the Iceman and a soldier frozen for 93 years on a glacier.
"The results support the hypothesis that ancient human gut microbiomes are more similar to those of non-human primates and rural non-western communities than to those of people living a modern lifestyle in the United States. From these data, the team concluded that the last 100 years has been a time of major change to the human gut microbiome in cosmopolitan areas."
The past hundred years has also been a time of greatly increased life span expectancy, both at birth and adult life expectancy at any age. There are plenty of obvious candidate mechanisms to point to when explaining these gains: control of infectious disease; improved medical technology across the board; rapidly increasing wealth and all the benefits that brings to the individual.
So there is no great incentive or missing cause that might drive one to go digging around in the microbiome of the gut in search of the degree to which changes there might influence life span. But it is interesting to speculate on that topic in advance of the studies that might provide an answer one way or another - which I would expect to require a great deal of time and work, given that the effects of medicine and wealth are comparatively large. Teasing out smaller effects from population studies is a challenging task.