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A slice of dark rye bread spread with hummous, a bowl of fragrant dahl cooked with onion, a piece of watermelon ... if the friendly microbes inhabiting your gut could send out for their favourite meals, these foods would be on the list. What they all have in common is that they contain specific types of fibre that act as prebiotics - meaning they provide fodder for the good bacteria that help to keep us healthy.
Our body's need for fibre is no longer just about beating constipation and reducing the risk of heart disease - research into gut health now suggests that encouraging the right balance of gut bacteria can do a lot to improve our health in other ways. One example is the gut microbes that produces a substance - butyrate - that helps protect the bowel lining from cancer, providing you keep feeding them the right stuff; that alone should be enough reason to dust off your dahl recipe.
So what are these special fibres and what should we eat to get enough of them? One is resistant starch found in legumes, as well as in barley, firm bananas and cooked and cooled rice - this is the fibre favoured by those microbes defending your bowel lining, says Dr Jane Muir, Head of Translational Nutrition Science at Monash University's Department of Gastroenterology. Another important group of fibres - called short-chain oligosaccharides - are found in nuts, seeds, onions, garlic, Jerusalem artichokes and watermelon, as well as legumes and grains.
"These fibres feed other friendly microbes that produce fatty acids that are absorbed into our bloodstream and which may be important for reducing inflammation - meaning the kind of low grade chronic inflammation in the body that contributes to problems like heart disease and diabetes," Muir says.
An easy way of getting more of these fibres is by eating legumes and wholegrains - but these are also foods that some people have struck off the menu, including anyone who's avoiding grains containing gluten or who's following the Paleo Diet which excludes both grains and legumes.
"We're a bit worried about people on these diets because they may miss out on these important fibres, "Muir says.
"Some people do need to be on diets that restrict these foods. For example, if you've been diagnosed with irritable bowel syndrome then limiting them will help control gastrointestinal symptoms associated with IBS. If you've been diagnosed with coeliac disease then you also have to avoid foods containing gluten - but some people restrict gluten for other reasons, thinking it will help with weight loss or improve bloating. But by restricting grains like rye, barley and wheat you miss out on these indigestible carbohydrates that are so important for gut health."
The Paleo diet which aims to mimic a traditional hunter gatherer diet embraces vegetables, nuts, lean meat, poultry and fish but avoids grains and legumes as well as dairy foods.
"It's a healthy way of eating in some ways because it's based on whole foods and avoids processed foods but it's a diet that makes it difficult to get enough resistant starch - although you could probably get enough short chain oligosaccharides on a Paleo Diet if you ate enough onions, nuts, seeds and Jerusalem artichokes," Muir says.
For the rest of us her advice is to include more legumes in the diet because they're a good source of both resistant starch and short chain oligosaccharides, and suitable for people with coeliac disease because they're gluten free. "They're a powerhouse of these fibres - and they're also filling and cheap."
We're also still only scratching the surface of our understanding of gut microbes and how they can affect our health, she adds - it's a question of 'watch this space'.
"The next challenge is finding out what's the ideal population of microbes to have in the gut and how to get them."
- Sydney Morning Herald