8 things to know about the gut microbiome and keeping yours healthy : NPR

The gut microbiome is a hot topic in wellness and health circles, often attracting both interest and dubious claims. This complex community of bacteria and microorganisms in our intestines significantly influences our health beyond just digestion, affecting our immune system, mood, cognition, and metabolism.

As public awareness of the microbiome’s role in our well-being grows, so does the market for advice and products claiming we need to continually test and optimize this internal ecosystem. However, researchers in the field caution that many of these claims outpace current scientific evidence.

Here’s what leading scientists want you to know:

1. Defining a “healthy” gut microbiome is challenging

Determining what constitutes a healthy gut microbiome remains complex. The microbiome’s composition can vary widely among healthy individuals, influenced by factors such as geography, lifestyle, diet, and genetics.

Despite significant advancements in the field, Hannah Holscher, a professor of nutrition at the University of Illinois in Urbana-Champaign, notes there’s still no clinical or scientific consensus on what a healthy microbiome looks like. This lack of consensus means there’s no simple metric for assessing gut health, unlike cholesterol or blood pressure levels.

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Generally, scientists recognize certain characteristics of a healthy microbiome. Research indicates that a higher diversity of microorganisms can be beneficial. Other factors include the microbiome’s ability to withstand disruptions like illness or antibiotics and to recover afterward. Some groups of bacteria have been linked to health, though these are not universal indicators since, in some cases, greater diversity might relate to certain diseases.

2. It’s about function, not just composition

Identifying beneficial groups of bacteria is only part of the puzzle. It’s also crucial to understand their functions. Scientists have found certain bacteria associated with better health and have studied their roles in the lab.

Experts warn against oversimplifying the distinction between “good” and “bad” microbes. Dr. Alexander Khoruts, a professor at the University of Minnesota, explains that issues might arise from the entire microbial community’s dysfunction rather than a single microbe causing problems.

A major study surveyed over 40,000 human gut microbiomes globally and identified key bacteria groups that contribute to health and resilience, such as Roseburia, Eubacterium, Faecalibacterium, Allistipes, and Bacteroides. Although causation isn’t proven, Holscher highlights common beneficial traits among these microbes, like fermenting fiber, producing healthful metabolites, and creating short-chain fatty acids.

For instance, Roseburia, enriched by consuming certain nuts, produces butyrate, a short-chain fatty acid that nourishes colon cells, supports the gut lining, and creates an acidic environment that deters pathogens like E. coli.

The challenge is that two healthy individuals can have vastly different microbiomes, leading to varied responses to the same diets and interventions.

3. The modern microbiome has challenges, but it’s not hopeless

Contrary to the bleak portrayal on social media, our modern microbiomes aren’t beyond repair. Dr. Fergus Shanahan, an emeritus professor at the National University of Ireland in Cork, suggests that while industrialized microbiomes have suboptimal aspects, they have adapted to our environment.

Living in industrialized societies has impacted our gut health. Factors like antibiotic use, diets low in fiber and high in refined foods, sedentary lifestyles, and environmental influences are detrimental to our microbiomes. However, Shanahan cautions against assuming we’d be healthier with a pre-industrial microbiome. For people moving from pre-industrial to industrialized settings, this change might increase their risk of obesity and chronic diseases.

Moreover, what was once normal isn’t always healthy. For example, Helicobacter pylori was common and possibly protective against some autoimmune and allergic diseases, but it is now known to increase the risk of peptic ulcers and stomach cancer.

Shanahan emphasizes the evolving nature of our microbiomes, noting that what benefits us at one point may not be beneficial later.

4. Over-the-counter microbiome tests yield uncertain results

With technological advances, products claiming to reveal your gut health have emerged. These tests, often based on stool samples and costing a few hundred dollars, promise detailed insights and a gut health score. Yet, the appeal of mapping your microbiome to find solutions is misleading.

Khoruts observes that patients often bring these test results to him, believing they reveal something their doctors missed. However, he cautions that they aren’t very informative. The lack of a standard definition or metric for a healthy microbiome, coupled with individual variations, renders these tests clinically meaningless.

Additionally, research indicates technical inconsistencies in these tests, with different companies producing varying results from the same sample. These direct-to-consumer products aren’t held to the same standards as diagnostic tests ordered by doctors.

5. What about probiotics?

The supplement aisle offers a dizzying array of probiotics claiming to support various aspects of health. Experts have established three key criteria for probiotics: the microbes must be alive, present in adequate amounts, and proven to have health benefits.

Shanahan warns that commercial products often gloss over the requirement for proven health benefits, despite claims of being “clinically tested.”

“Consumers need to be cautious,” he advises.

Researchers agree that probiotics have potential, with some strains backed by high-quality data showing efficacy in specific situations. For example, certain probiotics can reduce the risk of antibiotic-associated diarrhea, severe complications in preterm infants, respiratory tract infections, and travelers’ diarrhea, and help manage some inflammatory bowel diseases.

Contrary to popular belief, probiotics are not meant to permanently colonize the gut but temporarily stimulate the immune system, intestinal lining, and gut-brain axis to produce beneficial compounds during use, says Maria Marco, a professor of food technology at UC Davis.

“I’ve seen probiotics make a difference in people’s lives,” Marco says. “But their efficacy depends on the specific microbe, person, and timing.”

6. What helps? Fiber and fermented foods

Long before the term “fibermaxxing” became popular, people consumed fiber for its health benefits. Experts recommend increasing fiber intake from nuts, fruits, and vegetables as a powerful way to boost the gut microbiome. Currently, most Americans don’t meet the recommended daily intake of 20 to 40 grams, depending on age and sex.

Diversity in fiber sources also matters. “Different foods, like apples, oranges, and avocados, offer various fibers and phytonutrients,” Holscher explains. “Different microbes use these fibers for energy.”

Research shows that significantly increasing fiber intake can relatively quickly alter the microbiome. Holscher advises doing this gradually.

Her lab found that even modest dietary additions, like a handful of nuts or an avocado, can enrich beneficial bacteria within weeks.

Adding fermented foods like kimchi, kefir, and sauerkraut to your diet can also be effective. A Stanford study found that adults who increased fermented food consumption for 2 1/2 months had greater microbial diversity and reduced inflammation markers.

Yogurt is an easy way to add probiotics to your diet, but opt for products with live cultures and avoid those with added sugar.

Khoruts notes, “Fermentation produces chemicals like lactic acid that may benefit the gut.”

7. What to avoid

While many foods are criticized online, gut health experts emphasize the importance of overall dietary patterns rather than focusing on individual foods. Holscher says that as long as you maintain a diverse diet, occasional sugar-filled treats are permissible.

She and others recommend that most of your diet consist of whole foods, whether plant or animal-based, while minimizing foods high in refined sugars and saturated fats.

There is increasing evidence linking ultra-processed foods to gut diseases and microbiome changes. Animal studies suggest artificial sweeteners, additives, and emulsifiers may be harmful, though the science remains inconclusive.

Holscher advises limiting alcohol to maintain gut health. Research suggests heavy drinking can disrupt the microbiome, harm the gut lining, and cause other issues.

8. Lifestyle matters

Our gut microbiome is closely connected to our overall physiology. When our bodies thrive, our gut microbes are likely to be healthy as well. Sleep, exercise, and psychological well-being are lifestyle factors that can significantly impact our gut microbiome, either positively or negatively.

Khoruts explains that people experiencing gut issues like bloating, cramps, and constipation—assuming no underlying condition—can see significant improvements by making simple lifestyle adjustments.

Shanahan believes that research supports the common-sense advice you might receive from a grandmother: “Microbiome science hasn’t discovered a magical solution for perfection,” he states. “There’s no need for a health guru to claim they have a potion to enhance your microbiome.”