Dec. 17, 2019

How do you eat to feed trillions? Food and the health of our gut microbiomes

Each of us carries around a huge host of microbes that we're born with, that changes over time, and that programs our immune system over the course of our lives. Research shows that what we eat has the most influence over this microbiome, and the largest impact on its health.

When we think of food, we think of its role in nourishing and sustaining our bodies. But a rapidly growing body of research is showing that what we eat also affects our microbiome — all the viruses, bacteria, germs, fungi and other microscopic creatures who live in and on our bodies — and that the health of our microbiome plays a huge role in our own health. So before you eat your dinner, just remember it's in your best interest to be a gracious host to trillions of guests you didn't invite, and likely didn’t even know existed.

“Don’t just feed yourself — feed your gut microbiota,” says Dr. Raylene Reimer, PhD, who is a professor and associate dean of research in UCalgary’s Faculty of Kinesiology. “I know it’s a little strange to hear that we have to start focusing on providing proper nutrition to the bacteria in our intestinal tract — our gut microbiota — but we now know that optimizing our health means not just eating to feed our bodies, but our microbiota as well.”

Reimer is slated to hold a lecture about the topic Feb. 6 at the Canadian Museum of Nature in Ottawa. It will be part of a university-sponsored exhibition at the museum called Microbiome: The Secret World Inside You, from Dec. 20 to March 29.

What is the gut microbiome?

Scientists use two terms to describe the microbes in our body. Microbiota describes the collection of microbes that form a community. Microbiome represents those microbes plus all of their genetic potential, which is useful in telling us not just who’s there, but what they’re doing.

Rather than simply being along for the ride, the bacteria in our gut play a role in our lives that’s far greater than their tiny size would suggest, says Reimer. Along with that lab requisition for a blood test, the day is likely coming when your family physician will also send you off to get your gut microbiota checked out, she says.

“They are tremendously influential on our health,” says Reimer, who is also a professor in the Department of Biochemistry and Molecular Biology at the Cumming School of Medicine.

“The gut microbiome can provide great benefits that help maintain and promote our health, or it can become disrupted and trigger a wide range of chronic diseases,” she says. “Given that diet is one of the largest modifiers of our gut microbiome, we need to step up our efforts to reinforce the principles of healthy eating.”

We're all walking ecosystems

Like the fish in a coral reef or the animals in a rainforest, these trillions of bacteria that naturally live in our intestines collectively form a community made up of hundreds of species.

“They continually communicate with each other, compete for food, and seek out niches to colonize, making it both a cooperative and a competitive community,” says Reimer. “The microbiota is also affected by the things we do, such as taking antibiotic drugs or eating a high-fat, low-fibre diet, which can disrupt the balance in the microbial community.”

Researchers increasingly see such disruptions — or dysbiosis— as a factor in everything from asthma, autism and allergies to obesity, diabetes, arthritis, heart disease and cancer, says Reimer. She adds they even play a role in mental health conditions such as anxiety and depression.

How can “bugs” in your intestine that you can’t even see with your naked eye possibly affect your brain? “It’s really fascinating that things we once thought of as completely separate — our brain and our gut microbiota — are actually linked by a gut/brain superhighway,” says Reimer.

Scientists have shown that because of the hormonal and chemical signals the microbiota sends out in the gut, they can impact many distant sites in the human body, including the brain. This gut/brain link has inspired researchers, including Reimer, to investigate whether the power of the gut microbiome can be harnessed to treat common diseases, including those she is currently studying: obesity, autism, anxiety, and obsessive compulsive disorder.

Eat your veggies — your gut will thank you

The gut microbiota mostly feeds on a variety of dietary fibre left over from the food we eat, which is typically derived from the tough parts of plants that our bodies lack the enzymes to digest.

It’s the very same fibre from things such as fruits and vegetables that nutritionists — and parents everywhere — have been telling people for years to eat because it’s good for them. It turns out this fibre is also vital for maintaining a healthy gut microbiome, ensuring the community of bacteria stays robust and balanced in its relationship with our bodies, says Reimer.

“We have a mutualistic relationship with many of these bacteria — there is a benefit to both sides,” she says. “Bacteria get fibre from us, which is their main fuel source, and in turn they help keep our intestinal system and immune system functioning properly.”

Studies have not only shown that people likely derive much of their gut microbiomes from their mothers in infancy, the results of unhealthy diets have been shown in mice to be handed down as many as four generations, says Reimer. “Parents eating a low fibre diet passed on fewer healthy bacteria to their offspring, eventually putting many of these good bacteria at risk of becoming extinct by the fourth generation,” she says.

We have a mutualistic relationship with many of these bacteria.

The unhealthy, low-fibre diet of many Canadians, which often consists of processed foods heavy in saturated animal fats or refined sugars, has been shown by researchers to dramatically affect the gut microbiomes of mice. It not only starved many of the bacteria, causing the total population to plummet, it also changed the mix and type of species.

The mutually beneficial relationship between the mice and their gut microbiome was disrupted. Deprived of fibre, some species of bacteria disappeared from the microbiome or instead fed on the intestinal mucus layer, which became thinner, bringing the surviving bacteria closer to the intestinal wall.

This sparked an immune system reaction in the mice that led to chronic inflammation, which research has shown is a factor in many health problems and diseases ranging from obesity to cancer and type 2 diabetes. The intestines of the mice actually shrank, and the animals also experienced things such as elevated blood sugar and increased body fat.

Prebiotics vs. probiotics

Reimer wants to know if such disruptions in the gut microbiome of humans are also responsible for mental health conditions and diseases, “and more importantly, if they are disrupted, can we rescue the healthy bacteria with better diets, particularly fibre, to improve the symptoms?”

A study in 2017, co-authored by Reimer, looked at overweight children aged 7 to 12 who were otherwise healthy. The gut microbiota of the group that was fed prebiotic supplements of oligofructose — a type of fibre found in foods such as bananas and onions — was improved, showing higher numbers of healthy bacteria. Researchers also noted a significant decline in things such as body fat compared to a group that was given a placebo.

Can we rescue the healthy bacteria with better diets?

Prebiotic and probiotic supplements may potentially be a useful tool in the fight against many diseases and conditions, says Reimer. “Although probiotics are more widely recognized by the public, there is a growing interest in prebiotics,” she says.

“Probiotics are live microorganisms which, when administered in adequate amounts, confer a health benefit,” she says. Probiotics can be in capsule form, or they can be added to foods such as yogurt, she says.

“Prebiotics are ‘substrates’ that are selectively utilized by host micro-organisms conferring a health benefit,” says Reimer. “In other words, a prebiotic is a food that feeds the healthy bacteria that already live in your intestine.”

Many of the diseases that Reimer and others are studying are very complex. “While probiotics and prebiotics are unlikely to cure these diseases, they have the potential to help improve symptoms, and it’s that hope that drives the research forward,” she says.

Reimer conducts research at the university’s International Microbiome Centre, which opened in 2017. “It’s world-renowned, particularly the germ-free facility where mice are raised in completely sterile conditions, so they have no microbiota,” she says.

“If we want to investigate questions like: ‘What does this particular bacteria do when we put it into the animal? Does it affect anxiety-like behaviours in the mouse? Does it cause them to become obese?’, we have a world-class facility right here at the University of Calgary to do that research.”

Microbiome over the lifetime

Part of the picture that is emerging from such work is how the gut microbiome changes over the course of our lives, says Reimer. “Up to 90 per cent of all the bacteria in an infant who is breastfed is Bifidobacterium, which is a highly beneficial bacteria that helps train our immune systems,” she says.

This early period of rapid childhood development and growth is when infants are most vulnerable to microbiome disruptions that can affect their long-term health, says Reimer, who is also a member of the Alberta Children’s Hospital Research Institute.

Studies have shown that the children of mothers who are given antibiotics during pregnancy are more prone to obesity and asthma, leading researchers to suspect that mothers play a vital role in seeding the gut microbiomes of their babies, she says. “The ideal situation for establishing a healthy gut microbiota in early life appears to be a vaginal versus a caesarean-section birth; breastfeeding versus formula feeding; and no exposure to antibiotics,” she says.

“By the time we’re about three years old, our microbiota resembles the microbiota of an adult. While things like what you eat and whether you take antibiotics continue to influence your microbiota throughout life, it is aging that eventually causes the types of bacteria to once again start to shift.”

Keeping up with a healthy diet high in fibre becomes even more important as we age.

Researchers see the gut microbiome as a factor in human longevity and healthy aging. “As we age, our intestine starts to age as well,” says Reimer, adding the onset of frailty and diseases such as Alzheimer’s is also marked by a decline in the number and species of bacteria in the gut microbiome. “Keeping up with a healthy diet high in fibre becomes even more important as we age, feeding the gut microbiota and helping to avoid problems such as constipation,” she says.

In general, it is vital for people of all ages to avoid foods that disrupt the gut microbiota, says Reimer. “Diets that are high in fats — particularly animal or saturated fats — high in refined sugars, and high in processed foods with low fibre content and multiple stabilizers and preservatives, have all been shown to disrupt the healthy community of bacteria.”

“Disrupting the gut microbiota can trigger other problems, such as causing the gut to become leaky. The intestine acts as a barrier to keep out bacteria, but when the microbiota are imbalanced, this barrier weakens and lets bacterial products ‘leak’ into our bloodstream. This in turn triggers inflammation in the intestine and other tissues in the body.”

How to improve your microbiome

The best thing you can do for the health of both yourself and your microbiota is to cook at home as much as possible using natural ingredients, says Reimer. “Studies have shown that foods common in the Mediterranean diet are good for the gut microbiota,” she says. This includes plenty of vegetables and fruits, and whole grains, nuts and seeds.

Although so-called fad diets are enticing for many people, Reimer says we should be careful about how these diets may affect our gut microbiota. For example, a gluten-free diet is absolutely essential for people who have celiac disease, but many people without the illness are also adopting it, assuming it is healthier than eating foods derived from grains such as wheat, she says.

“While the diet has been promoted to the general public as a way to help you lose weight or make you healthier, it has been shown to decrease the amount of some healthy bacteria in the gut, such as Bifidobacterium,” says Reimer. “Some studies have also shown an increase in a type of bacteria that can cause inflammation, which might reflect the low fibre content of many gluten-free products that are on the market today.”

In general, moderation is best, even during traditional times of overindulgence such as Thanksgiving and Christmas, she says. “Start the day with a hearty, healthy breakfast, watch how many calories you consume in fancy drinks, and above all eat ‘microbiome-friendly’ foods every day, including lots of fibre from whole grains, vegetables and fruits, along with more yogurt, sauerkraut and other fermented foods that contain probiotics.”

Exercise is likely also important because it promotes a higher diversity of species within the microbiome, says Reimer. “Scientists are still trying to figure out how exercise might affect the microbiome, but it may be related to alterations in how quickly food moves through our digestive tract when we exercise,” she says.

“Typically, the higher the diversity, the higher the number of species in the gut microbiota, and the better the health outcome, so we can assume this is another reason why exercise is good for us. Not only does it directly help lower our risk of cardiovascular disease, improve our mood and help with things such as anxiety and depression, it is also probably good for the gut microbiota.”

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Dr. Raylene Reimer, PhD, RD, is a professor and associate dean of research in UCalgary’s Faculty of Kinesiology and a professor in the Department of Biochemistry and Molecular Biology at the Cumming School of Medicine. Her research interests focus on understanding the full potential of nutrition to prevent and treat obesity and type 2 diabetes. Read more about Raylene

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