How Probiotics & Prebiotics Keep the Microbes in Your Gut Healthy

Bacteria gets a bad rap. Most headlines focus on the danger and discomfort posed by pathogens like bacteria, but many of the bacteria that live on and in us are vital to our health. Many products out there, called probiotics, are sold with the implication that they're supporting these healthy bacteria that share our bodies — but do they actually work?

Inside and outside of your body is a teeming community of bacteria called microbiota, collectively called the human microbiome.

American Nobel Laureate Joshua Lederberg, a molecular biologist, was the first to use the term microbiota. The term and definition continue to evolve as we learn more about the microorganisms that share our bodies. These microbes, for the most part, are considered symbiotic, meaning that we share a beneficial relationship with them.

Trillions of bacteria make up the vast population of microorganisms that is you. Living on and in your skin, nose, respiratory tract, hands, hair follicles, and internal organs, the largest part of your microbiome resides in your gut. Composed of up to one thousand different species of bacteria, the microbiome is also home to fungi, viruses, and pathogens.

The study of the microbiota is fast adding to our knowledge of how our body works and thrives. Just some of the ways that microbiota are important to our health include:

• Microorganisms in the gut and intestine help digest proteins, carbohydrates, and other needed nutrients, as well as synthesize certain vitamins.
• The microbiome plays an important role as a barrier between pathogens and our bodies in the gut.
• In the intestine, the microbiome resists microorganisms that disrupt the stability of the bacterial community.

Your microbiota is uniquely you and arrived via the placenta before you were born. After that, your microbiome reflects where you have been, what you eat, and the conditions in which you and your microbiota live.

Research underway at Massachusetts General Hospital involves giving freeze-dried fecal material (yes, that means poop pills) to obese patients to study how seeding their digestive system with bacteria from healthy weight adults could help them lose weight.

While some of the science is looking carefully at the function of your microbiota, still other research involves finding ways we can feed and care for our own trillions of bacteria.

The Big Question: Do Probiotics Actually Work?

Our knowledge of microbiota is rapidly developing and changing. A relatively young field, the science of gut bacteria has been quickly taken up by industry. Most drugstores sell probiotics in some form or another, and yogurt and other fermented foods are frequently hailed as healthy for the gut because they contain live bacteria.

Probiotics are food or supplements that contain living microbes intended to support or improve your microbome's health. If your favorite yogurt contains "live and active cultures," you are getting a dose of probiotics along with your breakfast. These microbes are thought to bolster or replace the bacteria communities in the gut of people.

While there are many opinions on their effectiveness, there is not yet a clear answer that probiotics, or any particular supplement, are of guaranteed value. While foods can have an impact on the composition and health of the microbiota, if these foods specifically do, is still a big research question.

In one study, published in the International Journal of Nutritional Sciences, investigators from the University of Foggia in Italy determined lactic acids found in dairy products have a beneficial impact on intestinal bacteria that are involved with reducing inflammation.

"The bacterial community of gut is involved in the transformation of dietary compounds that could have beneficial effects," the study says. "Thus, some kind of food compounds also exert significant effects on the intestinal environment, changing the gut microbiota composition and probably its functional effects on human organism."

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While probiotics sound like a good idea and could potentially be helpful, gut bacteria are not a "one size fits all." It is highly unlikely that probiotics from a bottle will match the unique composition of your own internal bacteria landscape.

That said, if you've been ill or taken antibiotics and your intestinal bacterial populations have gotten out of whack, probiotics may aid in helping the microbiome recover, or bolster other functions until the native population of bacteria can recover. According to Harvard Medical School, the bottom line is that probiotics appear to help some people when they're sick, but others, not so much.

So ... What the Heck Is a Prebiotic?

While probiotics are living microorganisms intended to boost the numbers of your intestinal bacteria, prebiotics are types of food you're supposed to eat to nurture and feed your own personal microbiome (or bolster the potential positive effects of the bacteria in probiotics). As they say, "you are what you eat," and that matters in your gut.

In a study released in The British Journal of Nutrition from the Biofrontiers Institute and Howard Hughes Medical Center at the University of Colorado, researchers explained that "research on the effects of dietary interventions has shown that the gut microbiome can change dramatically with diet." Prebiotics are, for the most part, foods intended to feed your microbiome.

Arriving in the intestine, these fiber-full foods provide a balanced diet for your gut bacteria. Foods like bananas, raw or cooked onions, raw garlic and leeks, and jicama are a few good prebiotic choices. Also consider tomatoes, whole grains like bran, rye, and wheat, or fruit like plums and apples.

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Prebiotics are added to foods as well, under names like inulin, galacto-oligosaccharides, and fructo-oligosaccharides, among others. A key feature of these compounds and foods is that they are fermented by gut microbiota. Fermentation is a chemical process where foods or compounds are broken down by living microorganisms — like gut bacteria.

Certain types of fermented foods make great gut food, but processing is a critical step that determines how helpful the fermented food will be. Products that use bacteria, like sourdough bread, have little use as fermented food for gut bacteria because the bacteria died in the baking process. The same thing goes for anything that is heated to purify or stabilize shelf life — the healthy bacteria are killed.

Fermented foods that fit the bill include kimchi, certain types of cheese, yogurt with live cultures, miso, kombucha, kefir, and fermented vegetables that have not been heated to kill the helpful bacteria.

When you put together a probiotic and a prebiotic, like yogurt and a banana for breakfast, you are eating a synbiotic combination. Think of it as probiotics delivered with their own lunchbox. Good combinations include yogurt with a grain or apple, or feta cheese with beans.

What's the bottom line? According to the National Center for Complementary and Integrative Health, "Although a great deal of research has been done on probiotics, much remains to be learned."

Until more information on the microbiome, probiotics, and prebiotics are known, it looks like a healthy, diverse diet, rich in plant material and fiber — and low in fats and sugars — is a good bet for you and the trillions of bacteria that make up your own microbiome.

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Cover image by Dennis van Zuijlekom/Flickr