10 ways to improve your gut health - and have a profound impact on your overall health, according to food scientists
Is gut flora the new frontier of human health? A growing body of evidence suggests that the diverse species of bacteria which colonise the surface of our colon are engaged in an elegant and delicate dance with other physiological systems in the body and that their quality and quantity (or lack thereof) can have a profound impact on everything from inflammation, metabolism, autoimmunity, allergies, asthma obesity and even, on psychological issues such as anxiety and depression.
Some bacteria are responsible for reducing inflammation, others are linked with disease.
But alongside a growing understanding of the importance of an individuals "microbiome" on his or her overall health, comes a lot of hype.
Here, we consult the experts for advice on which lifestyle measures are most likely to favour a diverse, thriving microbiome.
1 Power of prebiotics
"The impact of diet is clear," say Dr Paul Cotter, a research scientist from the APC Microbiome research centre in University College Cork, which is leading the way in research in fast-changing area of the human microbiota. "Fibre (including whole grains and prebiotics) encourages the growth of many desirable microbes in the gut (especially in the colon)," he says, "and results in them producing beneficial bioactive compounds such as short chain fatty acids."
Dr Michael Mosley, GP, the BBC's Trust me I'm a Doctor and the author of The Clever Guts Diet explains that certain, specific types of foods called prebiotics help feed the good bacteria. "A prebiotic is a specific type of plant fibre which your body can't digest, but which encourages the growth of 'good' bacteria in your gut. The good gut bacteria turn that prebiotic fibre into chemicals like butyrate...(which) has powerful antiinflammatory effects inside the bowel. Prebiotics act a bit like fertiliser, boosting the growth of 'good' bacteria."
Good news for people who are fans of onions, leeks, garlic, Jerusalem artichoke, asparagus and bananas, as all of these foods are classified as prebiotics.
Dr Paul Cotter has been involved in some groundbreaking studies carried out at UCC which demonstrate that highly active individuals have healthier microbiomes than those who are sedentary.
"The role of exercise is less clear but we have performed studies which show that some athletes have very high levels of gut microbial diversity (desirable) and that this correlated with their diets and levels of exercise. We are doing follow-up studies to see if we can improve the gut microbiome of people in the general public through different exercise regimes," he says.
3 Get fermenting
"Ferqmented foods (kefir, kombucha, kimchi, sauerkraut) contain living microbes and other microbes that can also have beneficial effects," explains Dr Cotter. "There is a lot of hype around fermented foods so we and others are trying to carry out more scientifically rigorous studies to definitively establish their benefits (and how they differ from one food to another).
Dr Mosley agrees. "One of the reasons why fermented foods are so good for the gut is that, gram for gram, they contain a huge number of different microbes," he writes in The Clever Guts Diet.
"The microbes in fermented foods are also far more likely than most other bacteria to make it safely down into your colon, because they are extremely resistant to acid, having been reared in an acidic environment. You might worry about the impact on your gut of eating foods which are acidic, like sauerkraut and kimchi, but all the evidence shows that they are good for you."
Though he adds a note of caution to "start slowly if you haven't eaten these sorts of food before."
4 Try probiotics
"There's a lot of hype around probiotics" says Dr Mosley, who suggests that rather than necking pricey supplements, the best way for a healthy person to get them is through food, especially those foods that contain high levels of live bacteria.
He's a particular advocate of homemade yogurt and also recommends cheeses, singling out Gouda, mozzarella, Cheddar, cottage cheese, and especially feta, which, he says is filled with lactobacillus plantarum, known for producing antinflammatory compounds.
5 Avoid unneccesary antibiotics
Just one course of antibiotics can have a damaging effect on the gut flora that lasts for up to a year, according to a 2015 study published in the journal mBio. "Even a single antibiotic treatment in healthy individuals," the authors concluded, "contributes to the risk of resistance development and leads to long-lasting detrimental shifts in the gut microbiome with health-associated butyrate-producing species becoming strongly underrepresented."
In effect, some kinds of antibiotics decimated the numbers of strains of bacteria which produce butyrate - a fatty acid that helps regulate inflammation in the intestines.
Dr Michael Mosley cautions that the deleterious effect of antibiotics on intestinal health is particularly pronounced in the very young, which explains why "being exposed to repeated courses of antibiotics when you are a child also increases the risk that you'll become overweight, particularly if those antibiotics are given in the first six months of life."
6 Avoid an elective c-section and breastfeed if you can
These two factors won't impact the mother's microbiome, but might have a significant effect on the future health of her baby. Babies who are born by caesarean section have been observed to carry a very different population of gut bacteria compared to those delivered vaginally, according to study from the Harvard T.H. Chan School of Public Health, which found that "babies who are born by caesarean section are far more likely to become obese children and overweight adults."
They also have an elevated risk of allergies.
"Breastmilk contains complex sugars which, oddly enough, babies can't digest," says Dr Mosley.
"It seems that their main purpose is to feed the 'good' bacteria which are, hopefully, growing in the baby's gut.
"The fact that breast milk evolved to feed these Old Friends shows just how important they are."
7 Open a window
With modern buildings increasingly hermetically sealed, with reduced flow of air and bacteria between indoor and outdoor environments, the ranges of species of bacteria that we are exposed to on a daily basis are being altered. Open a window to let those good bugs from the outdoors in.
8 Get dirty
Rocketing rates of allergies and asthma in children have been linked to our increasingly sanitised, indoor-dwelling lifestyles.
"If your child has been out in the garden and comes in with slightly grubby hands, I, personally, would let them come in and munch a sandwich without washing," says Professor of Medical Microbiology Graham Rook, who also advocates spending time outdoors, with animals and on farms.
9 Avoid artifical sweeteners
A study carried out at the Weizmann Institute demonstrated that mice who were fed water laced with saccharin developed glucose intolerance within six days of being introduced to the new diet. The mechanism? An overabundance of the types of bacteria in their intestines that favour the development of obesity and diabetes.
This, according to Dr Mosley, is because "some gut bacteria react to sweeteners by secreting chemicals that provoke an inflammatory response, which in turn encourages obesity and diabetes."
10 Cut back on processed foods
A study published in the scientific journal Nature in 2015 provides hints that common food additives found in industrially produced ice cream, mayonnaise, cakes and biscuits might be responsible for the contemporary upsurge in rates of diabetes and obesity, because of these chemicals damaging effect on gut flora. The problem lies with emulsifiers, which are used to create smooth textures in processed foods.
The study, which was led by immunologist Andrew Gewirtz at Georgia State University, was carried out on mice. Those mice exposed to the highest levels of emulsifiers in their diet became obese and developed metabolic problems. They were also found to have less diversity of microbial species in their guts. The effect was the most pronounced in those mice that had been genetically engineered to be prone to gut inflammation.
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