Testing the truth behind probiotics
Our writer does a gut check with surprising results
Over the past 25 years, probiotics have emerged as a powerful way to treat some digestive ills. And recently, probiotic supplements have started to be used for a new purpose: to help generally healthy people stay healthy or get healthier. The concept has taken ferocious hold, with probiotics showing up in drinks, foods and cosmetics – even pet food.
This phenomenon led me to my nearest pharmacy with plans to conduct my own informal experiment. I would start by getting the microbial composition of my relatively healthy gut assessed using an online service. Then I would take probiotics for a month and test my gut again to see if the supplements had an impact. I hoped I would see an improvement in my microbiome – that’s the colony of trillions of bacteria that live in our bodies and that researchers have recently identified as a key to good health.
After spending 20 minutes reading labels to choose a supplement, I’m no closer to a decision than I was when I entered the store. The shelves host a bewildering array of brightly coloured boxes packed with live microbes. The label of one probiotic supplement promises digestive wellness and immune support. Another claims to enable weight loss, and a third offers “delicious chocolate taste”. I read each label carefully but soon become overwhelmed. Should I go for the extra-strength formula with five times more good bacteria, or do I want something “for a woman’s unique needs”?
Finally I ask the pharmacist for a brand my doctor once recommended, a cocktail of three bacteria – roughly equal parts Lactobacillus acidophilus and Bifidobacterium lactis, plus a dash of Bifidobacterium longum. When he retrieves it from a fridge in the back of the store, I see that this “extra high potency” bacterial concoction “naturally restores and maintains intestinal health,” according to the package. That seems promising.
I send in a specimen for analysis, then swallow the first pill from the probiotic package.
TEEMING WITH LIFE
While the enthusiasm for probiotics is relatively new, the idea goes back more than a century, to a Russian biologist named Elie Metchnikoff. He blamed nearly all the ailments of old age on bacteria in the colon, which he deemed a “vestigial cesspool,” and proposed a novel solution: eating milk turned sour (yoghurt) by one particular strain of what he believed to be beneficial bacteria. These good microbes, he reasoned, could replace bad bacteria and slow the ageing process. He adopted his own strategy and was “very well pleased with the result,” he wrote.
Even Metchnikoff might have been surprised to see how this notion of consuming advantageous bacteria has taken hold. Around the world probiotics are now big business and the market, including supplements and probiotic foods and drinks will exceed a staggering $64 billion in the next five years according to a report by Global Market Insights.
Behind this craze lies a wealth of scientific research. Over the past decade, researchers have come to realise that the bacteria that live on and in our bodies can profoundly influence our health. Microbes populate the gut, urinary tract and lungs and live on our skin and in our mouths. These invisible inhabitants help shape our immune systems, fend off infections, regulate our weight, and even potentially influence our emotions. So it makes sense that ingesting beneficial bacteria might restore balance to that ecosystem and cure – or at least soothe – some of what ails us.
Human studies provide support for this theory: certain strains of bacteria have been shown to alleviate the symptoms of irritable bowel syndrome, and some may help stave off the
diarrhoea associated with taking antibiotics and having certain infections. Other studies show that probiotics can enhance our ability to digest the lactose in milk and other dairy products.
FAR AHEAD OF THE SCIENCE
Evidence supporting any positive effect in healthy people, though, is scant. And most of the microbiome benefits touted by companies that manufacture and market probiotics are hypothetical.
One review published in 2016 looked at seven different randomised controlled trials examining the effects of probiotics on the gut microbiomes of healthy people. The authors found no evidence that probiotics had an effect on the diversity or richness of the microbiome, compared with a placebo.
That’s not surprising. The probiotics sold today tend to wash out of the gut before they can replicate.
“You often read that they are supposed to colonise and then reshape the microbiome,” says microbiologist Jens Walter. But “there is virtually no evidence that that can actually happen.”
For one study published in 2015, researchers recruited 59 healthy volunteers, gave them probiotics or a placebo, and exposed them to rhinoviruses, which cause the common cold.
The researchers didn’t see any statistical difference in the presence of the viruses between people who took the probiotics and those who didn’t. “There’s no compelling evidence that continued consumption of probiotics if you’re healthy has any benefit,” says Jack Gilbert, head of the University of Chicago’s Microbiome Center.
A similar study from the University of Virginia in 2017 showed that probiotics had no significant effect on the infection rate of rhinoviruses or the symptoms they cause.
RESULTS REVEALED
Nothing particularly notable happened during the month I ingested 15 billion bacteria. I didn’t feel different, and I wasn’t sure that the microbiome sequencing test would reveal any changes inside my gut either. Also, many of the researchers I spoke to weren’t convinced that
the comparatively small number of bacteria in my probiotic supplement would even show up.
My first test had shown good microbial diversity. When my second results came in, however, I could see a dramatic, and entirely unexpected, shift. I might have gained a couple of kilo or so over the month, but nothing unusual. At the same time, the diversity of my microbiome plummeted from the 54th percentile to the 11th. Low diversity has been linked to obesity and inflammatory bowel disease.
I asked clinical biochemist Daniel Almonacid to look at my results, but I didn’t mention I’d taken probiotics. He immediately homed in on the second sample, the one I collected on the last day of my probiotic trial. “The second sample is very weird,” he said. “I would say you were taking antibiotics.”
That was not what I expected to hear. Scientists have shown antibiotics tend to have catastrophic effects on the microbiome. Probiotics, by definition, are supposed to confer a health benefit. Why did I experience such a stark change?
VARIETY IS THE SPICE OF LIFE
The answers aren’t clear. “One of the largest influences on microbes and their activities in the gut is diet,” says Susan Lynch, a researcher at the University of California. But I didn’t eat any differently when I was conducting my experiment.
One explanation is simply that the microbiome varies from day to day. Microbiome researcher Rob Knight, has sampled his gut every day for the past nine years. “There’s a lot of variation from time point to time point, even when there’s nothing in particular going on,” he says. I had only two snapshots a month apart.
Probiotics that affect one person won’t necessarily cause the same shift for another. “There’s no way we can say that probiotic consumption is going to work for everybody,” Lynch says. “Microbes are not docile organisms.” They grow, divide, and respond to what’s in their environment, including other microbes.
While it’s difficult to draw any meaningful conclusions based on my brief, one-woman experiment, the results seem to underscore what the scientific literature suggests – which is that for now, probiotics have yet to live up to their promise for healthy people.
That could change. Scientists are now using what they’ve learned about the microbiome to develop cocktails of organisms that could be more potent and possess more staying power.
But until those next-generation bacterial therapies arrive, I’ll ignore the hype and focus instead on adding more microbe-friendly foods to my diet to help my gut bacteria flourish.