Along with trashing many of the planet's rainforests, many of us modern humans have also messed up another ecosystem - the microbes living inside our gut - says science writer and TV presenter Dr Michael Mosley in his new book The Clever Guts Diet.
Mosley, author of The Fast Diet, has turned his attention to the links between these microbes and our health - including their influence on our weight and our immune system and how what we eat can encourage a healthy diverse population in our guts.
"Like animals in the wild, many species in our gut are in decline. It's partly because we eat such a narrow range of foods which means our gut bacteria also have to live on a restricted diet," he says.
Other reasons for this lack of diversity include widespread use of antibiotics and also some emulsifiers used in food manufacturing - emerging research in animals suggests these food additives alter the balance of gut microbes. Yet we need our gut bacteria to be as diverse as possible to prevent potentially harmful species from taking over, Mosley explains.
Eating a wide range of plant foods rich in different fibres and colours can help increase diversity, he says, and while five serves of veg a day is good, Mosley stresses the need to put a bigger variety of vegetables on the menu rather than eating a limited few.
Seaweed could turn out to be good gut food too. Researchers from University College, Dublin have found that when seaweed extract is fed to sows, their piglets have less harmful bacteria in their gut and need fewer antibiotics, while a study in humans from the University of Wollongong found that taking capsules containing seaweed fibre for six weeks resulted in an increase in bacteria which produce substances that promote a healthy gut lining.
Besides highlighting gut-friendly food, Mosley gives us a peek inside his own gut via the results of a screening test to identify the key microbes living there. A number of companies now offer this test online - you pay for the cost of a test kit ($89 is the starting price for a kit from uBiome, for example), send them a poo sample and they send you the results.
The who's who of microbes in Mosley's gut included:
Bacteroidetes. These made up just over half of his gut bacteria - a good thing because according to the company that did Mosley's test, a microbiome tilted in favour of bacteroidetes is associated with less inflammation in the gut. These microbes also break down undigested fibre in the gut, producing beneficial substances including butyrate which helps keep the gut lining healthy and has anti-inflammatory effects.
Akkermansia. Mosley had good levels of these microbes which, like bacteroidetes, strengthen the gut wall. When Belgian scientists gave akkermansia to overweight mice it stopped them becoming obese and developing diabetes. According to Mosley, eating more polyphenol-rich foods (e.g. olives, tea, dark chocolate and coffee) can boost levels of akkermansia.
Lactobacillus His levels of this helpful bacteria were low - lactobacillus helps protect the gut from unfriendly pathogens and can be depleted by antibiotics. Some research suggests that some strains of lactobacillus taken as a probiotic can improve depression.
Bifidobacteria. Mosley had higher than average levels of these bacteria which break down indigestible fibre and, like lactobacillus, help protect the gut from less friendly microbes. We inherit bifidobacteria from our mother's breast milk. Mosley credits his own high count with his love of cheese and yoghurt which contain the bacteria.
Is it worth doing what Mosley did and find out which microbes inhabit your gut?
By itself, an analysis of your gut microbes isn't particularly useful unless it's to tell you there are no high levels of disease-carrying bacteria, says Associate Professor Andrew Holmes from the Charles Perkins Centre at the University of Sydney.
"If you're a healthy person you're unlikely to gain any new insights you can use to change your life for the better. If you have a chronic disease such as type 2 diabetes or obesity which is linked to an imbalance of gut microbes then a test may detect this imbalance, but at the moment this alone can't show how you can improve your health." he points out.
That said, some studies have found that an analysis of gut microbes, along with other information on your health, diet and genetics can provide clues as to how to use diet or other measures to improve your health, he adds.
"As our understanding of gut microbes and their interaction with our diet and immune system grows we expect to soon reach a point where microbiome analysis will be a key test for many diseases.
"Although getting a microbiome analysis might not change your treatment options at the moment, people who get it done should think of this as contributing to a vast citizen science project that will lead to a new tool in healthcare."
The Clever Guts Diet by Michael Mosley is published in June by Simon & Schuster, $29.99.
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