Intestines have become a subject of endless fascination.
Social media influencers are promoting unproven supplements that claim to improve gut health, while milk and kombucha brands promise to feed them good bacteria.
Some dismiss the gut obsession as a passing fad, but many doctors believe that our gut microbiome can affect a whole range of things, from mental health to the likelihood of developing certain cancers.
But there's another medical possibility that personally interests me: how our gut influences how well (or poorly) we age.
Which is why, a few months ago, I found myself at St. Mary's Hospital in London, famous for the discovery of penicillin, ready to gain a shocking insight into the health of my own gut.
I'm here to meet with Dr. Jameson Kinross.
He's a professor of surgery at Imperial College London and a practicing colorectal surgeon, but perhaps the most colorful part of his job is analyzing people's poop.
A few weeks earlier, I sent a stool sample to the lab.
Tests like this can provide insight into our gut microbiome - the billions of microbes that live in our stomachs (mostly bacteria, but also viruses and fungi).
“I’m a microbiome preacher,” he says.
"It is deeply embedded in all aspects of our health."
He believes that the gut could play a key role in the aging process - with consequences for how long we live and how physically strong we remain in our later years.
Some experts believe that the importance of the gut microbiome to the aging process has been overstated, and everyone I spoke to thinks more research needs to be done.
Now that I'm in my sixties and recently became a grandfather, it seems like the right time to discover what my own gut is telling me about how I'll fare in the coming decades.
And to get an answer to a broader question: if gut health can really affect aging, is there anything, and what, that we can do to improve it?
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117-year-old woman and her daily yogurt
Maria Branyas Morera was the oldest person in the world.
After she died in 2024 in northern Spain, at the age of 117, scientists took samples of her stool, blood, saliva and urine, and compared them with 75 other women from the Iberian Peninsula.
They say she led a broadly healthy lifestyle: she lived in the countryside, walked for an hour a day, and ate a Mediterranean diet rich in oils.
But what really made her stand out was the fact that she drank yogurt three times a day, every day.
Dr. Manel Esteler, a geneticist at the University of Barcelona who co-authored the study, thinks Morera's yogurt habit led to high levels of beneficial bacteria that reduce inflammation.
"She had cells that looked younger than her actual age," says Esteler.
There have been other studies done on centenarians - superheroes of the world longevity.
Time and again, scientists have studied the guts of this blessed population of over 100 years old and discovered an impressive array of bacteria.
In another study, published in 2022 in the journal Nature (Nature), researchers from Jiaoling County in southeastern China, took stool samples from 18 centenarians - and found a high diversity of bacteria compared to younger adults.
Guts should be 'as diverse as a garden'
This makes sense to Dr. Mary N. Lochlane, a clinical lecturer in geriatric medicine at King's College London.
She says it's helpful to think of our gut microbiome as a garden: we want it to be as diverse as possible.
“If you walk into a garden where there are no plants and it looks bare, it’s a low diversity garden,” she explains.
"You want lots of flowers, colors, seeds."
The problem is that as we age, the diversity of our guts declines significantly.
Some of the beneficial bacteria are disappearing from our intestines.
But seniors who buck this trend—and who manage to keep their good bacteria in their eighties and nineties—turn out to live longer, healthier lives.
For Ni Lochlane, these studies are proof of the connection between our gut and aging.
"We know that centenarians have a more diverse microbiome."
"There's something about these people that are kind of superior beings, in a way. They've managed to preserve their own diversity."
And it's not just about how long someone lives - it's also about how well they live in their later years.
Kinross says there is a link between gut bacteria and frailty, or an older person's ability to recover from illness or injury.
My real age compared to the age of my intestines
In the lab at St. Mary's Hospital, Kinross delivers his verdict: I have good "gut microbiome diversity."
"He is generally healthy," which is good news.
But I can sense some reservations in his tone.
And, of course, they are coming.
First, he explains that there are several “gut players” that could increase the risk of cardiovascular disease.
Quite disturbingly, some nasty germs were also found.
Escherichia coli and clostridia are also present, which is not uncommon.
(They could have been caused by antibiotic use or a previous bout of gastroenteritis.)
But then we come to the question of age.
Kinross tells me that my gut biome is roughly equivalent to an Italian five years older than me.
He calculated this by comparing my results with a study conducted on 62 people in northern Italy.
In the study, the only one of its kind, researchers analyzed stool samples from people of different ages, ranging from 22 to 109 years old, allowing them to paint a portrait of what a person's intestines look like at different stages of life.
His verdict makes me think, with a twinge of guilt, about all those years of eating ready-made meals and snacks.
The grueling work hours reporting on the 2008 banking crisis and the Covid pandemic led to too many cookies and snacks being devoured on the go.
Living in London on and off since my twenties meant living on traffic fumes, rather than the cleaner air of northern Italy.
No wonder my intestines have been declared five years older than me.
Kinross must have seen the color drain from my panicked face, because he immediately began to assure me that perhaps the Italians all followed a Mediterranean diet or lived in rural areas untouched by city pollution.
Plus, it was a study done on a small sample.
He further reassures me by saying that all the "machinery for healthy aging" is there, it just needs to be optimized.
In other words, if I can deal with my own diet, there is time for improvement.
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Can you 'hack' your gut health?
As for whether people can improve their own aging process through diet, Esteler is optimistic.
He points out that some "uncertainty" remains about the link between gut health and aging, but says the evidence is pretty clear that what we put on our plate can affect both our "morbidity and our mortality."
In other words, how long we live or how likely we are to remain in good health throughout our later years.
"Even in the same city, among people with high incomes, those who eat better live longer," he says.
He recommends eating olive oil, which contains polyphenols that boost bacteria; and oily fish, a sharp-toothed seafood that is rich in fatty acids and popular in Japan, which boasts one of the highest life expectancies in the world (84,5), according to the World Health Organization.
Bluefish, however, is difficult to obtain in most British supermarkets; it can generally only be found in specialist fishmongers or restaurants.
He also recommends avoiding refined white sugar and ultra-processed foods whenever possible, which can disrupt the diversity of bacteria in your gut.
But Esteler points out that some people will have more luck than others in trying to "hack" their own intestines, and genes also play a big role.
Kinross cautions that research into how the microbiome functions in different population groups is still in its infancy.
For now, he says, each patient should be assessed individually.
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A 'turning point' for older people
Armed with his report, I make an appointment with Raquel Bricke, a dietitian, who reviews the findings and writes me a menu plan to boost the diversity of my gut bacteria in the hopes that it will help me age better.
Her plan was tailored specifically to my results.
For the first few days of the week, she suggests I make a bowl of flax seeds, chia seeds, kefir, blueberries, kiwi, and pomegranate for breakfast.
(That's not too far from my normal bowl of oatmeal with a little sugar and yogurt.)
For lunch, he recommends a green salad, beans or lentils, broccoli, asparagus or beets, and grilled skinless chicken.
This seems a little heavy.
These ingredients aren't always easy to find when you need a quick snack between two journalistic assignments.
And for the evening meal, it's salmon, asparagus, and brown rice.
With a raised eyebrow, my wife expresses doubts that I will be able to stick to it every night.
As for drinks, I was recommended juices.
On the first day, I diligently blend mint, apple, kiwi, kale, lemon juice, sunflower seeds, and water to make a green juice.
But the mint flavor ultimately overpowers all the others.
Kefir and kombucha (fermented drinks rich in bacteria) are also recommended and they suit me better.
Both now have a place in my fridge.
Rakel Bricke also recommends that I take capsules with probiotics such as Omega-3 and Vitamin D3.
They are not cheap and it is difficult to remember the specific time of day when they should be taken (some, but not all, on an empty stomach).
Kinross tells me that a nutritional change has to be “significant” to have an impact on aging.
If I strictly adhere to the new eating plan, he says, I could change my gut biome “within a few weeks,” he explains.
But he warns that a more "modest" change in diet - for example, if I do it one day but not the next - the biome will not benefit much.
And therefore, any improvement in the appearance of aging is also much less likely.
I still have time, he tells me.
But there will really be a “tipping point” for older people when the gut biome deteriorates.
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The “chicken or the egg” problem for the intestines
And there's another conundrum - one that Nee Lochlane calls the "chicken or the egg" problem.
And that is: does a more diverse gut make us stronger in old age, or does the fact that we are older in old age make us have a more diverse gut?
Historically, it has been difficult to determine which of the two causes the other.
But even that question may now be answered, thanks in part to research into fecal transplants - where feces are taken from one human or animal and given to an animal (usually a mouse) via a capsule or tube into their stomach.
In one such study, published in 2020, scientists in the US followed two groups of 11 healthy mice.
The first group received feces from old mice; the second group received them from young mice.
Within three months, the mice that were given old feces began to exhibit depressive behavior.
Their short-term memory deteriorated, as did their spatial orientation.
Their bodies practically became older.
Mary N. Lochlane accepts that this may sound unpleasant to many people, but these studies are important because they suggest a direct causal link: from the gut biome to the age of the body.
Not everyone is excited about our gut's power to control our aging.
Professor Camilla Hawthorne, president of the Royal College of General Practitioners, says research into the gut microbiome is "exciting" and "has certainly piqued public curiosity".
But, she adds, “it’s important to remember, especially since research in this area is still in its infancy, that ‘gut health’ is likely just one piece of the puzzle in a much bigger picture.”
"Good health is not determined by just one factor."
Ultimately, scientists say it's possible to improve the aging process through your diet, although they warn that food isn't everything.
Esteler estimates that diet probably determines about one-third of your aging outcomes.
The rest is a mix of genetics and other lifestyle factors, such as exercise and avoiding cigarette smoking.
As for my own gut health, it's still too early to judge the impact of my new diet.
My appetite is satisfied and I'm not tempted by snacks, except for the recommended apples, grapes, and nuts.
But in a busy lifestyle with unpredictable hours, sticking to this kind of meticulous plan will have difficulty and I doubt my own ability to pull it off.
Still, the tests and the trip were a wake-up call for my own gut and my future health.
Additional reporting: Luk Minc
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