A new paper explores adjusting the types of bacteria in the gut as a potential way to improve health in older people.
The gut microbiome is a fascinating and diverse ecosystem filled with a myriad of bacteria, archaea, protists, fungi, and viruses that interact with each other and our bodies in diverse and complex ways.
In recent years, it has become increasingly apparent that the condition of the gut and the microorganisms living within it can have a significant influence on health and, by association, longevity. Aging, in particular, is known to have an impact on the populations and diversity of the microbiome, with the levels of different bacteria rising and falling, which then has a downstream effect on health.
In early 2019, a study in China looked at the microbiomes of healthy, long-lived people aged 90 to 100+ and observed that such people had gut microbiomes that were similar to those of younger people .
Intriguingly, previous studies have demonstrated that health can be improved by restoring the balance of gut microbial populations to more youthful levels. A 2019 study showed that transplanting gut microbes from young to old mice reverses immune decline , and a recently published paper builds on this.
Modifying the microbiome to improve health
This new paper explores modifying the gut microbiome to increase production of butyrate and brain-derived neurotrophic factor (BDNF) in order to improve cognitive function .
Butyrate is one of the key short-chain-fatty-acids produced by gut bacteria via the breaking down of fiber in the gut, and the body uses it for a variety of functions. In particular, butyrate is a key compound in the creation of the energy that colonocytes, which line the intestinal wall, feed upon.
It is proposed that age-related changes to the bacteria lead to a decline of butyrate production, resulting in a condition known as “leaky gut”, in which the intestinal wall is compromised and leaks bacterial products deeper into the body, driving inflammation and disease. It is likely that other cells also rely on a supply of butyrate to maintain health.
BDNF is a protein that interacts with neurons in the central and peripheral nervous system, helping to support the survival of neurons, and it encourages the growth of new neurons and synapses. It is especially active in the hippocampus, cortex, and basal forebrain, which are parts of the brain that are crucial for learning, memory, and higher thinking. BDNF is also produced in the retina, motor neurons, kidneys, skeletal muscle, and other tissues.
These researchers discuss adjusting the gut microbiome in rats in order to increase the levels of butyrate and BDNF and thus improve cognitive function.
The process of aging underlies many degenerative disorders that arise in the living body, including gradual neuronal loss of the hippocampus that often leads to decline in both memory and cognition. Recent evidence has shown a significant connection between gut microbiota and brain function, as butyrate production by microorganisms is believed to activate the secretion of brain-derived neurotrophic factor (BDNF). To investigate whether modification of intestinal microbiota could impact cognitive decline in the aging brain, Romo-Araiza et al. conducted a study to test how probiotic and prebiotic supplementation impacted spatial and associative memory in middle-aged rats. Their results showed that rats supplemented with the symbiotic (both probiotic and prebiotic) treatment performed significantly better than other groups in the spatial memory test, though not in that of associative memory. Their data also reported that this improvement correlated with increased levels of BDNF, decreased levels of pro-inflammatory cytokines, and better electrophysiological outcomes in the hippocampi of the symbiotic group. Thus, the results indicated that the progression of cognitive impairment is indeed affected by changes in microbiota induced by probiotics and prebiotics. Potential future applications of these findings center around combatting neurodegeneration and inflammation associated not only with aging but also with the damaging posttraumatic effects of ischemic stroke.
This study builds on an increasing amount of evidence that the gut microbiome has a significant influence on health and thus longevity. It also strongly suggests that adjusting the types and numbers of bacteria in the gut to more closely emulate a youthful microbiome may be a viable approach to improve health in older people.
 Feilong Deng, Ying Li, Jiangchao Zhao (2019). The gut microbiome of healthy long-living people. doi.org/10.18632/aging.101771.
 Stebegg, M., Silva-Cayetano, A., Innocentin, S., Jenkins, T. P., Cantacessi, C., Gilbert, C., & Linterman, M. A. (2019). Heterochronic faecal transplantation boosts gut germinal centres in aged mice. Nature Communications, 10(1), 2443.
 Heyck, M., & Ibarra, A. (2019). Microbiota and memory: A symbiotic therapy to counter cognitive decline?. Brain Circulation, 5(3), 124.