Walk through any supermarket and you’ll see a vast array of products touting their “friendly bacteria.” We’ve become accustomed to the idea that our guts are a bustling metropolis of beneficial microbes, and that a daily dose of yogurt can keep them happy. This cozy, mutually beneficial relationship seems simple: we give them a home, and in return, they help us digest food and stay healthy.
But what if this picture is only half the story?
A growing body of evidence reveals a more complex reality. As we age, a “dark cabal” of unfriendly bacteria begins to take over, slowly but surely wreaking havoc on our bodies. Far from being simple allies, our gut microbes play a key role in the negative aspects of aging, including disease, frailty, and the decline of our immune system.
The good news? We can harness the power of the microbiome to help us age better and avoid ill health.
The Gut Microbiome: A Balancing Act
Our gut microbiome is a complex ecosystem of over 100 trillion microorganisms—bacteria, viruses, and fungi—weighing as much as a small hamster. Established at birth and shaped by diet, environment, and lifestyle, this microbial community remains relatively stable for decades. During our younger years, beneficial bacteria like Roseburia and Bifidobacterium dominate. They break down dietary fiber, produce essential nutrients like vitamins K and folate, and keep the bad guys in check.
However, from around age 50, the balance starts to shift. The good bacteria decline, while the “bad guys,” such as Escherichia and Streptococcus, begin to flourish. This loss of microbial diversity is a hallmark of aging. Dr. Aimée Parker of the Quadram Institute notes that the gut microbiome of an 80-year-old looks vastly different from that of an 18-year-old. More importantly, it’s also different between healthy older adults and those suffering from conditions like frailty, Alzheimer’s, and Parkinson’s disease.
Studies have identified specific microbial “signatures” linked to common age-related diseases like type 2 diabetes and cardiovascular disease. The question, for a long time, was whether the microbiome drives aging or if aging changes the microbiome. We now know the answer is both.
The Gut-Brain Connection: What Happens in the Gut Doesn’t Stay There
Research using Faecal Microbial Transplants (FMT)—or “poo transplants”—has provided startling insights. When microbes from old animals were transferred to young ones, the young animals developed signs of accelerated aging. In mice, this led to memory impairment, and in flies, it shortened their lifespans.
Dr. Parker’s work with mice showed that receiving “old” microbes caused age-related changes in the gut, eyes, and brain, including increased inflammatory markers in the brain and a depletion of key proteins for vision. “What happens in the gut doesn’t stay in the gut,” she says, underscoring the systemic impact of our microbial community.
As the unfriendly bacteria take over, the gut wall deteriorates. It becomes inflamed and “leaky,” allowing microbes and their byproducts to enter the bloodstream. This triggers a chronic, low-level inflammation known as “inflammageing,” a recognized driver of many age-related diseases, including cancer and heart disease. This microbial disruption even affects the immune system directly, as microbial products reach the thymus gland, a key part of our immune defense. Dr. Niharika Duggal of the University of Birmingham suggests this microbial mayhem contributes to the age-related shrinking of the thymus.
A Path to Better Aging
The good news is that the microbiome is incredibly malleable. The slide toward microbial disorder can be slowed, which is almost as beneficial as preventing it entirely. Reverse faecal transplants in mice—where young microbes are given to old mice—have shown remarkable results: reduced inflammation, a less leaky gut, improved immune function, and even better cognitive performance.
While faecal transplants for anti-aging are still in the clinical trial phase, researchers are exploring less invasive methods, such as freeze-dried capsules.
Another potential strategy is the use of prebiotics and probiotics. Prebiotics are fibers that feed healthy bacteria, while probiotics contain the bacteria themselves. Early studies are promising. One study found that a prebiotic supplement decreased frailty in older adults, while others showed probiotics reduced markers of inflammation. Research is also exploring postbiotics—the beneficial chemicals produced by healthy bacteria, such as butyrate, which can help reduce inflammation and protect the gut wall.
However, many experts caution against rushing to buy off-the-shelf supplements. Microbiome researcher Prof Fergus Shanahan advises against wasting money on supplements, noting that it’s nearly impossible to know what your unique gut needs, and tests can quickly become outdated. “One measurement doesn’t mean much anyway,” he says.
The Single Best Thing You Can Do
So, what is the most effective, accessible way to support your microbiome? The answer is surprisingly simple: eat a healthy diet rich in fibre.
“Just eat more fibre. Fibre is microbe food,” says Shanahan.
Study after study highlights the benefits of a Mediterranean diet, which is rich in vegetables, fruits, fish, olive oil, and nuts. This diet is already known to improve longevity and reduce the risk of chronic diseases. The largest study of its kind found that older adults who switched to a Mediterranean-style diet for one year had more of the “good” bacteria linked to healthy aging and less of the “bad” bacteria associated with inflammation.
This is the first clear evidence that a healthy, fiber-rich diet can actively combat the gut bacteria that drive unhealthy aging. But you don’t have to wait until you’re older to start. As Shanahan concludes, “If you want to prepare for old age, it’s best to prepare when you’re young… The one thing we can all do to help deterioration in old age, is to add diversity to our diet now.”
