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How To Feed Your Gut Microbiota

Are you feeding your gut microbes the right fibre?

How to feed your gut by Leslie Beck RD

If you’re like most Canadians, you don’t eat enough fibre. And even if you are meeting your daily fibre target, you might be focused on getting lots of one particular kind, such as wheat bran to prevent constipation or psyllium to lower blood cholesterol. Either way, you’re likely short-changing your good gut bacteria the special type of fibre – called resistant starch – they need to thrive to keep you healthy.

Without a steady supply of resistant starch, the healthy microbes that reside in your gut can die off, increasing the load of disease-causing bacteria. Running down the good guys may also increase the risk of allergies, type 2 diabetes, obesity, and inflammatory bowel disease.


Your gut is home to trillions and trillions of microbes, the vast majority of them residing in the large intestine. Collectively, these bacteria, yeasts, and fungi make up what’s called your microbiota.

The terms microbiota and microbiome are often used interchangeably, but there’s a subtle difference. The gut microbiome refers to the gut microbes themselves (microbiota) plus the genes they contain.

Our gut microbiota extracts energy and nutrients from fibre, synthesizes certain vitamins, activates disease-fighting phytochemicals, regulates immune function and protects the lining of the gut. Growing evidence suggests this microbial community also plays a role in inflammatory bowel disease, mental health, weight control, even food cravings.

A gut microbiota that contains a diverse community of microorganisms is defined as a healthy one because it increases the likelihood of beneficial species and fewer pathogenic bacteria.

Each person’s microbiota is unique and always changing. Genetics, antibiotic use, hygiene, stress, and illness can shape the make-up of our microbiota.


Your diet is considered the most powerful tool that can alter the composition and activity of gut microbes.

A Western-style diet, high in animal protein, saturated fat and refined carbohydrates and low in fibre has been linked to a loss of microbiota diversity. Plant-based diets, on the other hand, have been associated with a richer, more diverse microbiota.

Large changes in your diet can alter your microbiota in just one or two days. Even so, it’s your long term dietary habits that count when it comes to the composition of your microbiota.


As its name implies, resistant starch escapes digestion in the small intestine and makes its way to the large bowel, where it’s slowly fermented and broken down by good bacteria.

Fermentation creates short-chain fatty acids, compounds that feed gut bacteria, fuel colon cells, prevent the growth of harmful bacteria, fortify the intestinal lining and help regulate immune function.

Good sources of resistant starch include white beans, chickpeas, lentils, green peas, cashews, unripe bananas, plantain, whole grain pumpernickel bread, wholemeal rye bread, barley, raw oats, and muesli.

The longer you cook food and the higher the temperature used, the more resistant starch will be lost. Rice, potato, yams, and pasta that have been cooked and cooled are decent sources of resistant starch, though. Cooling cooked starches change their structure making them resistant to digestion in the small intestine.

If you don’t eat enough resistant starch, good bacteria can feed on other things, which can damage the gut. The microbiota of mice starved of fermentable fibre have been shown to feed on the mucous lining of the gut, making it thinner and more vulnerable to infection-causing bacteria.


Not all high-fibre foods contain microbiota-friendly resistant starch. Insoluble fibre, found in wheat bran and whole wheat bread, passes through the digestive tract without being fermented. That doesn’t mean this type of fibre isn’t good for you. It promotes regularity and guards against diverticulosis.

Some, but not all, foods rich in soluble fibre – the type known to lower LDL blood cholesterol and stabilize blood sugar – are fermentable by the microbiota. Psyllium, for example, is poorly fermented whereas oats, barley, and some beans and lentils contain resistant starch.

Drink more water when increasing your fibre intake since fibre needs to absorb water to work effectively.

Eating for a healthier microbiome Research on how foods alter the microbiota, and, in turn, influence health is in the early stages, but it’s accelerating at a rapid pace. Studies suggest the following tips can help nourish your microbiome.

Eat more plants. Aim for your meals to be 75 percent plant-based. Fill three-quarters of your plate with foods such as whole grains, vegetables, fruit, beans and lentils and nut, and seeds.

Ditch the Atkins-style diet. A high-protein, low-carb diet won’t cultivate a robust microbiota. Findings from a 2011 study conducted in overweight men found that such a diet reduced beneficial short-chain fatty acids and antioxidants. It’s also thought that undigested proteins that reach the colon may promote the growth of harmful bacteria.

Increase resistant starch. Foods such as white beans, chickpeas, lentils, green peas, cashews, unripe bananas, plantain, whole grain pumpernickel bread, barley, raw oats, and muesli are good sources of resistant starch, a fuel that allows good gut bacteria to flourish.

So are cooked and cooled rice, potato, yams and pasta. Add leftover grains and pasta to salads to boost your fermentable fibre intake.

Add prebiotics. Studies show that supplementing your diet with non-digestible carbohydrates known as prebiotics can fuel the growth of Bifidobacteria and Lactobacilli, two common probiotic bacteria.

Prebiotic foods include asparagus, bananas, Jerusalem artichokes, jimica, rye, barley, kefir, leeks, onions, garlic, and chicory root. Foods high in resistant starch are considered prebiotics.

Consider a probiotic supplement. Taking a good quality probiotic supplement can help diminish microbiome damage caused by antibiotics. Specific species and specific strains of probiotics have also been shown to lower LDL cholesterol, manage constipation and ease bloating.


Leslie Beck is Medcan’s Director of Food and Nutrition.
She writes a weekly column in The Globe and Mail and is a contributor to CTV News and CBC Radio. Follow her on Twitter @LeslieBeckRD

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