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What to Know About Prebiotics And Probiotics

The latest research reveals that gut bacteria may be linked to blood glucose and body weight. Here’s how probiotics and prebiotics could help

By Karen Ansel, MS, RDN ,
illustration-stomach-vegetable-kefir-yogurt-MA20

Ekaterina Kapranova/Getty Images (food illustrations)

You’ve probably heard about probiotics, live bacteria in food believed to improve digestive health. Maybe you’re consuming them already. Or perhaps you’re just thinking about it. But what exactly are probiotics? And, more important, do you need them?

The Bacterial Balance

Your gut is a busy place. On the most basic level, it’s where digestion happens. It’s also home to 100 trillion live bacteria, collectively known as your gut microbiota.

It might sound creepy, but it’s not. Many of the bacteria that live in your gut do amazing things for your health, such as aiding in digestion, strengthening your immune system, producing vitamins, and helping metabolize nutrients. And that’s just the beginning. An ever-growing body of research suggests that these beneficial microbes may also have more widespread effects, improving your heart health, body weight, blood glucose, mood, and more.

At the same time, there are other bacteria living in the gut that are less desirable, and sometimes even harmful. Left unchecked, these may lead to obesity, digestive disorders, allergies, and possibly diabetes.

Unfortunately, many of the realities of modern life make it all too easy to tip the balance in favor of bad bacteria. Antibiotics, squeaky-clean homes, and a diet of highly processed foods that are stripped of fiber have all reduced the number and variety of healthful bacteria that inhabit the gut. “With fewer good bacteria on board, it’s easier for unhealthy bacteria to move in and take over,” says Elisabeth Almekinder, RN, CDE, a certified diabetes educator with the Manos Unidas North Carolina Farmworker Health Program. “That can weaken the immune system, making us more likely to develop chronic illnesses like diabetes.”

The Diabetes Link

Just like you have a distinct set of fingerprints, you also have a unique gut microbiota. Yet despite these individual differences, scientists have discovered striking similarities in some types of gut bacteria among people with certain health conditions. And one of those diseases is type 2 diabetes.

A study published in 2018 in the Journal of Diabetes Investigation reports that people with type 2 diabetes tend to have greater numbers of bacteria shown to promote inflammation than people who don’t have diabetes. While more research is necessary, experts suspect that these inflammatory microbes might contribute to the development of type 2.

There are also microbial similarities among obese people, who are at greater risk for type 2 diabetes. Research shows that people who are obese harbor more of a family of bacteria called Firmicutes than those who are lean. Yet when they lose weight, the amount of Firmicutes decreases and their microbiota begins to more closely resemble that of a lean person.

There’s also some evidence that certain bacteria may influence the way carbohydrates are metabolized. “Historically, the impact that a food has on a person’s blood sugar level was mainly thought to depend on their insulin levels or how resistant their body was to removing extra sugar from the blood,” says certified diabetes educator Julie Stefanski, RDN, CDE, a registered dietitian nutritionist and a spokesperson for the Academy of Nutrition and Dietetics. “However, several recent studies have shown people may have entirely different blood glucose responses to the same food based on their unique gut bacterial makeup.”

Prebiotic Power

Just as unhealthy processed food can lower the number of good bacteria in your gut, certain plant foods can prompt those helpful microbes to grow. These are known as prebiotics—indigestible fibers found naturally in foods such as  onions, leeks, garlic, leafy greens, flaxseed, chicory root, and oats.

Why are they so helpful? “When we eat foods containing prebiotics, we can’t digest their fibers, so they travel intact to the colon, where the real magic happens,” says Stefanski. There, beneficial gut bacteria ferment them and break them down for food. With a steady diet of prebiotics, good gut microbes are more likely to grow, thrive, and crowd out the bad bacteria that can lead to disease.

Nourish a healthy microbiota by eating plenty of prebiotic-rich fruits, vegetables, and whole grains. They can do more for your gut than probiotic foods alone. “Without a healthy dietary pattern rich in prebiotics to nourish healthy gut bacteria, optimal benefits of even the most effective probiotic may be limited,” says Moul Dey, PhD, a professor of health and nutrition at South Dakota State University.

Get to Know Probiotics

Your gut is populated with microbes, but sometimes the balance between bad and beneficial bacteria gets thrown off-kilter. Eating probiotics can help you improve or maintain the good bacteria in your gut. You can also get probiotics from supplements, but they may not offer the same benefits. (For details, see “Supplement Skepticism” below.)

Most diabetes experts recommend a diet-driven strategy. Fermented foods contain live cultures, microbes produced during the fermentation process, but not all fermented foods contain probiotics.

According to health authorities such as the National Institutes of Health and the World Gastroenterology Organization, probiotics are more than just live cultures. They have been rigorously and scientifically proven to deliver specific health benefits. Plus, unlike less-hearty live cultures, probiotics are able to withstand the harsh conditions of the human digestive system.

Fermented foods and drinks such as sauerkraut, kimchi, and kombucha get lots of press for their live cultures, but there’s no real proof they can improve gut health so they don’t technically qualify as probiotics. Instead, opt for yogurt and kefir, a fermented milk drink, which contain probiotics. (Look for the words “live and active cultures” on the label.) Teamed up with prebiotics, they make for gut-friendly fare.

What to Eat

Prebiotics: Asparagus, bananas, chicory root, flaxseed, garlic, leafy greens, leeks, oats, onions

Probiotics: Yogurt and kefir with “live and active cultures”

Supplement Skepticism

If certain gut bacteria are linked to type 2 diabetes, can you improve blood glucose management by consuming specific probiotic or prebiotic supplements? Experts can’t say for sure.

“Unfortunately, consistent success with probiotic supplements in research is limited, especially for chronic conditions like obesity and diabetes,” says Moul Dey, PhD, a professor of health and nutrition at South Dakota State University. “It may seem like the scientific community has learned a lot about probiotics, but the information we do not know far [outweighs] what we do know.”

The vast majority of research points to the potential of probiotic supplements to improve digestive health, mainly by alleviating constipation and by preventing antibiotic-associated diarrhea and traveler’s diarrhea. What’s more, “people vary considerably with regard to their age, lifestyle, underlying physiology, genetics, and individual microbiota and may therefore respond differently to the same [supplement],” says Dey.

There’s also the question of which probiotic or prebiotic is most advantageous. Each individual probiotic strain is responsible for a distinct health outcome. So while Bifidobacterium lactis HN019 may be useful if you’re constipated, you’ll want Lactobacillus rhamnosus GG if you’re dealing with traveler’s diarrhea. But even if you were able to find the precise probiotic supplement for what ails you, there’s no guarantee you’re getting the strain or number of live bacteria listed on the label because supplements aren’t regulated the same way that drugs are. 

The bottom line: Skip the supplement aisle and instead load your shopping cart with prebiotic and probiotic foods. You’ll save money and reap the rewards of a healthier gut.

 

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