What lurks inside your intestines hardly seems a topic for conversation but as Kate Emery writes, waging a war against bad gastrointestinal bacteria could spell a revolution in health.
It is something polite people do not talk about.
What happens to food after it is eaten is something that makes schoolchildren squeal while most adults do their best not to mention.
Yet the gastrointestinal tract, better known as the gut, is having a moment.
Good bacteria, bad bacteria and, yes, poo, have become a serious part of the health conversation.
Giulia Enders’ book Gut — about “our body’s most underrated organ” — has become an international phenomenon. Michael Mosley, the British doctor behind the wildly popular 5:2 diet, has now turned his attention to bacteria with The Clever Guts Diet.
Closer to home, Australian celebrity chef and paleo diet spruiker Pete Evans is spruiking The Complete Gut Health Cookbook. Hipster-friendly Perth cafes are doing a brisk trade in turmeric lattes and kombucha brews, both feted for their gutfriendly properties.
The diet industry has been quick to board the bandwagon. Proponents of paleo, sugar-free and gluten free diets, among others, now serve them up with a side promise of good gut health.
“If the bad bacteria take over, then you get very sick." - Dr Paul Bertrand
If you believe the hype, a healthy gut can make you skinnier, happier and live longer.
But where do fad diets meet hard science? And exactly how can we target the bad bacteria and encourage the good bugs?
Everyone has bacteria inside them and lots of it: the human gut is teaming with bacteria, parasites, viruses and other bugs, collectively known as the gut microbiome or microbiota.
In a healthy gut, bad bacteria is “kept in check by the good ones,” says pharmacology and toxicology expert Dr Paul Bertrand, who has had more than 70 publications on the workings of the gastrointestinal tract and its impact on health and disease.
“If the bad bacteria take over, then you get very sick.
“If the gut community is functioning well, it helps to keep your immune system running smoothly, helps to keep your colon healthy and can help provide you with some hard to get vitamins and nutrients.”
The idea that a healthy gut means a healthy body is not new.
Hippocrates, popularly regarded as the father of modern medicine, claimed more than 2000 years ago that all disease began in the gut.
What has changed is that science knows a little more about how the gut works and how we can manipulate it.
Many studies have indicated that good gut bacteria reduces the risk of contracting certain chronic diseases, including diabetes, heart disease and obesity.
The idea of a gut-brain axis has also gained popularity, suggesting gut health could have implications for a range of conditions not obviously linked to digestion, such as Parkinson’s, autism and depression.
It is the link between microbiome and obesity that has the diet industry interested.
But the problem with bold claims about how to “fix” or “heal” the gut — and get skinny in the process — is that even the experts are not entirely sure what makes for a perfect gut microbiome.
Professor Tom Riley, Professional Research Fellow at ECU’s School of Medical and Health Science, puts it this way: “What is normal for me isn’t normal for you.”
“Everyone’s gone microbiome mad,” he says.
“This is not the panacea everyone makes it out to be. I think people are getting a bit carried away.”
The gut microbiome changes over a person’s life and can be impacted by diet, environment and the use of things like laxatives and antibiotics.
As anyone who has seen an ad for yoghurt in the past decade will know, probiotics — live bacteria found naturally in certain fermented foods and drinks — may also be able to improve the microbiome.
For this reason fermented foods like kimchi, kombucha and sauerkraut are promoted by some diet plans, including proponents of paleo and sugar-free diets.
Riley specialises in the study of Clostridium difficile infections (CDIs), a bacterium that can cause potentially fatal diarrhoea.
He is “a big fan of probiotics” to treat recurrent CDIs but says probiotics deserve more scientific scrutiny.
Bertrand also believes the ability of probiotics to cause a general health benefit has been “overstated”.
“Any benefits from probiotics generally need daily intake,” he says.
“Many large clinical trails have failed to find a benefit in healthy people of eating probiotics. If you are unhealthy there may be some short-term benefits from probiotics but a better way to improve gut health is to feed the bacteria that are already there.”
That means “feeding” bacteria with what are known as prebiotics —fibre found in beans, certain vegetables and grains that can boost the activity of good bacteria.
Bertrand is wary of exclusionary fad diets because they can deprive the gut bacteria of these and other nutrients.
Paleo diets generally advise against eating grains, legumes and sometimes dairy; gluten-free diets typically mean no pasta or bread and the most extreme interpretation of sugar-free means no fruit.
“Good health is most strongly associated with a large and diverse community of gut microbiota and you need to supply your gut with a variety of fibres and prebiotics foods to support this,” Bertrand says.
“The more different types of food you can supply your microbiota with, the more varied your gut community will be.”
ECU researcher Angela Genoni recently completed a study of 39 women, and found those on a paleo diet were more likely to experience diarrhoea than those following Australian dietary guidelines.
Just why the paleo diet affects the gut is not clear. But one explanation could be that the diet is low in resistance starch, which is found in potatoes, legumes and some grains and is believed to be good for gut health.
“The area of gut health is really huge at the moment,” Genoni says.
“What we are doing here will help put the pieces of the puzzle together. It just adds to the body of literature.”
Proponents of the paleo diet promote it as good for the gut, she says, but there is a lack of evidence for many of the claims.
“We don’t know. There’s no research on any of it,” she says.
Genoni says the simplest way to improve gut microbiome is to eat more fruit and vegetables.
Bertrand’s message is similarly reminiscent of what health professionals have been saying for years: eat more vegetables, less sugar and reduce portion size.
As for whether healthy people should be trying to manipulate their gut microbiome in the name of better health, the last word goes to Riley.
“All these people that want to do weird things (like) colonic irrigation, they’re going to do more harm than good,” he says.
“One shouldn’t get too hung up on one’s bowels.”
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