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Special Reports May 2017 Issue

Nourishing Your Microbiota

Eating a diverse, plant-rich diet helps fuel the growth of beneficial bacteria.

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Microbes - bacteria and other tiny critters not visible to the naked eye but numbering in the trillions - are busy in your body. Many of these microbes benefit you. Others have the potential to cause harm. This community of microbes is called the microbiota. Their genes are called the microbiome.

"In recent years, we've realized our microbiota performs functions - either directly or through the products they make - that could impact the functioning of our body," says Simin Nikbin Meydani, DVM, PhD, vice provost for research at Tufts University and director of the Nutritional Immunology Laboratory at the HNRCA. "For example, scientists are exploring how the microbiota may be involved in the maturation of the immune system, energy metabolism and how our brain functions."

That's not all. Disruption of the normal human gut microbiota has been associated with many different health conditions, such as asthma, allergies, irritable bowel syndrome, obesity, type 2 diabetes, cardiovascular disease and colorectal cancer, among others. Exactly what role the microbiota might play in these conditions is uncertain. But, it's wise to do your best to support a healthy microbiota.

Managing Your Microbiota:

Many factors impact the makeup of your microbiota, such as your genetics, age, sex, disease conditions, where you live and medications, such as antibiotics. A potentially big influence on your gut microbiota under your control is what you regularly eat.

Eating probiotic-rich foods like yogurt with "good bacteria" may be the first way that comes to mind for shaping the makeup of your gut microbiota. What some people don’t realize is that probiotics aren't one-size-fits-all. Research shows that certain benefits associated with probiotics, such as supporting immunity or easing constipation, are specific to the species and strain of bacteria. Fermented foods like yogurt typically only contain a few different bacteria, while our gut microbiota is estimated to contain about 1,000 different species.

Another way to influence your gut microbiota is by changing what you "feed" the bacteria. In recent years, scientists have been looking more closely at how what we eat influences which microbes thrive in our body. "There are several components of our diet classified as prebiotics that influence the growth of the microbiota or the products they produce," Meydani says. "Certain dietary fibers that are fermented by intestinal bacteria but not digestible by people are the main type of prebiotic recognized by scientists."

"There are other components of food that may also impact the microbiota," Meydani adds. "For example, there's some evidence that certain phenolic compounds (phytonutrients) may benefit the microbiota. There's also a good amount of evidence that certain lipids could impact the diversity and type of microbes that exist in our gut. We're just starting to learn about all of the different dietary components that could influence the gut microbiota."

Diversity Matters:

In general, the greater the diversity of the bacteria in your microbiota, the better off your health may be. A loss of diversity of the gut microbiota has been found in several disease conditions, such as obesity, type 2 diabetes and inflammatory bowel diseases (Crohn’s disease and ulcerative colitis), among others.

"We know fiber is protective against conditions like obesity and cardiovascular disease, and this could be related to fiber’s effect on the microbiota," says Hannah D. Holscher, PhD, RD, assistant professor of nutrition and director of the Nutrition and Human Microbiome Laboratory at the University of Illinois at Urbana-Champaign. "However, intervention trials to show that increased diversity of the gut microbiota is related to decreased incidence of disease are still ongoing."

"The strongest evidence we have that a diverse microbiota is beneficial comes from research on preventing and treating infections from disease-causing bacteria, such as Clostridium difficile," Holscher says. "When the diversity of the microbiota is depleted by antibiotic use, some people get Clostridium difficile infections. One of the main symptoms is severe diarrhea."

To treat Clostridium difficile infections, additional antibiotic treatments are necessary. However, for some people the antibiotic treatment doesn’t work well. Fighting the infection by improving the makeup of the microbiota may work better. "It's been shown that when physicians do a transplant of the microbiota from a healthy person or from a certified microbiota stool 'bank' (available at some hospitals) to the infected person, it can restore the microbiota to a healthier condition and stop the symptoms of the infection," Holscher says.

Promoting Microbial Diversity:

The diversity of the microbiota of individuals in the US consuming a typical Western diet low in fiber and high in processed foods is generally less than in people in unindustrialized rural communities (such as in some parts of South America or Africa), according to Holscher. That's partly because the latter group consumes more fiber.

Studies of cross-sections of people across the world suggest the more fiber you consume - especially if from a wide range of plant foods - the more diverse your gut microbiota will be. Additionally, intervention studies in people have shown that consuming more fiber and whole grains increases diversity of gut bacteria.

Different microbes are capable of breaking down (fermenting) different fibers. Holscher explains that it takes different enzymes to break down the various fibers found in foods. Some bacteria have many different enzymes, so they can utilize dozens of different fibers. Other bacteria may only be able to break down one or a few different fibers. By eating a variety of plant foods with different types of fibers, you may encourage the growth of a more diverse population of beneficial microbes capable of breaking down those fibers.

Next: Page 2: What Microbes Produce and Eating for Trillions

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