How Exercise Improves Microbiome Health (and Vice Versa)

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By Mary Grace Descourouez, MS, NBC-HWC 

The human gastrointestinal tract is home to trillions of microorganisms that create the gut microbiome. The gut is where the body digests and absorbs nutrients from our food and, therefore, where we get our energy to perform daily human functions. Microbiota are microorganisms in the gut microbiome that help the body harvest energy, fight pathogens, and regulate immunity. Having a high diversity of microbiota helps us to process food effectively, providing the substrates and nutrients needed to keep us going throughout the day. Therefore, it is crucial to make lifestyle choices that promote a healthy and diverse microbiome.

Many people know that a nutrient-rich diet contributes to a healthy microbiome, however, research shows that movement and exercise may also have a positive effect, and, inversely, a healthy microbiome may improve athletic performance.

“It is a relatively new field, but available studies suggest a bidirectional relationship between performance and the health of the microbiome,” says Anne Friedlander, PhD, Exercise Physiologist and Assistant Director of Stanford Lifestyle Medicine. “People who are more active have a healthier and more diverse microbiome, and that, in turn, provides the person with the nutrients required to enhance physical and cognitive performance. It is a mutually beneficial relationship.” 

How Exercise Improves the Microbiome

Movement and exercise have many benefits on our overall health, including positive effects on the microbiome. Studies show that athletes have a more diverse microbiome composition than non-athletes. Microbiome diversity is important because it helps make our food’s nutrients more bioavailable for optimal functioning of the body.

Another study found that active women were associated with high microbiome diversity compared to sedentary women. Specifically, researchers found that consistent physical activity increased the amount of 11 genera of “good” bacteria, including Bifidobacterium spp, Roseburia hominis, Akkermansia muciniphila, and Faecalibacterium prausnitzii. 

How the Microbiome Improves Athletic Performance

Just as exercise positively impacts the microbiome, emerging research shows that microbiome health may also play a part in enhancing exercise performance.

For example, a 2019 study showed that a specific gut microbiota in marathon runners may have enhanced their athletic performance on race day.  In this study, researchers collected fecal samples from the runners before and after the marathon and compared them to microbiota of non-runners. The “good” bacteria Veillonella emerged as the most common in the runners, especially post marathon. Veillonella is a bacterial strain that converts exercise-induced lactate into propionate, which is a natural enzymatic process known to enhance athletic performance.

Researchers then put the Veillonella bacteria from the marathon runners into lab mice who underwent a treadmill exertion test to investigate the hypothesis that this bacterial strain enhances athletic performance. The results showed the mice improved performance by 13 percent after inoculation. This study is one of the first to infer that a healthy microbiome could enhance athletic performance.

“We have a long way to go to fully understand the complex system that involves the microbiome and athletic performance, but the early data look promising regarding gut health and exercise,” says Dr. Friedlander.  “Exercise, along with eating fermented foods and fiber, is a great place to start if you want to improve your gut health and overall health.”

Probiotics, Prebiotics, and Postbiotics: What Are They and Why Are They Important?

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By Maya Shetty, BS

Key Takeaways:

  • Probiotic and prebiotic supplements lack substantial scientific evidence that they promote microbiome health. 
  • Rather than taking supplements, experts recommend eating fermented foods (probiotics) to promote microbiome diversity and fibrous foods (prebiotics) to feed and sustain “good” bacteria in the gut.  
  • Recommended fermented foods (probiotics): 
    • Fermented vegetables: kimchi, sauerkraut, and certain pickled vegetables
    • Fermented dairy: yogurt, cottage cheese, kefir, and certain cheeses
    • Fermented soy: tempeh and miso
  • Recommended high-fiber foods (prebiotics):
    • Legumes: lentils, chickpeas, black beans, and kidney beans
    • Seeds: chia seeds, flaxseeds, pumpkin seeds, and sunflower seeds
    • Whole grains: quinoa, brown rice, oats, and barley
    • Nuts: almonds, walnuts, pistachios, and pecans
    • Vegetables: broccoli, Brussels sprouts, artichokes, carrots, and sweet potatoes
    • Fruits: apples, pears, berries (raspberries, blueberries, strawberries), and bananas
  • Postbiotics, the byproduct of probiotic and prebiotic activity, not only reduce the risk of chronic diseases and support brain health, but also offer anti-inflammatory and beneficial metabolic effects.

Within our bodies, there exists a bustling community that often goes unnoticed but plays a pivotal role in our well-being—the microbiome. Understanding the impact of the microbiome on our health is not just a scientific curiosity, it’s a crucial aspect of our health that underscores our body’s complex equilibrium. Through continuous negotiations, our body and microbiome engage in a symbiotic relationship—a dynamic exchange where we provide our microbiome with nourishment and “good” inhabitants, and in return, it synthesizes beneficial compounds to support our health.

“We are, in essence, walking ecosystems. Our health is intimately connected to the trillions of bacteria, viruses, and fungi that make up this community,” states Sean Spencer, MD, PhD, Gastroenterologist and Physician Scientist at Stanford University.

The microbiome actively participates in various bodily functions, from aiding digestion and nutrient absorption to eliminating toxins and synthesizing vitamins and amino acids.

“The influence of our microbiome extends far beyond the confines of the digestive system, reaching major body systems like the immune system, metabolism, and the central nervous system,” states Rachele Pojednic, PhD, Stanford University  nutrition and exercise scientist.

While the definition of a healthy microbiome remains unclear, the majority of studies find that high microbiome diversity is linked to better health outcomes. “A healthy microbiome is one that is equipped to process a diverse array of dietary fiber to produce  health-promoting compounds for our body,” states Dr. Spencer. “Low microbiome diversity is linked to various health conditions, including diabetes and obesity and likely has reduced fiber-degrading potential and lower production of health promoting compounds.”

A recent study revealed that the average Californian has a microbiome that contains 277 microbial species, a stark contrast to the average of 730 found in non-industrialized populations. This finding aligns with a mounting body of evidence suggesting that modern lifestyles and Westernized diets have significantly depleted the essential diversity of our gut microbiome.

Therefore, many individuals have sought ways to manipulate their microbiome and increase its diversity via supplementation. Commonly referred to as probiotics and prebiotics, these supplements have surged in popularity, achieving sales of $35 billion in 2015 and projected to reach $65 billion by the end of 2024.

Despite their widespread use, there is significant confusion about what they are, where to find the best ones, and what they can and can’t do. Regardless, experts say the most powerful and beneficial sources for all your biotic needs are often overlooked (hint: they are in your refrigerator).

What Are Probiotics and Why are They Important?

Probiotics are live microorganisms that are consumed for health benefits and typically found in fermented foods like yogurt, kimchi, and sauerkraut. They play a crucial role in supporting our gut by introducing beneficial bacteria to our microbiome community. Simultaneously, they reduce the proliferation of harmful bacteria by constraining their available space for growth.

Upon hearing the term “probiotics,” many individuals associate it with the supplement pills that have long been advertised to improve digestive health. However, these supplements are not recommended over food, as they can displace favorable microbial residents in the gut.

“The doses of microbes found in supplements are overly potent, with billions to trillions of microbes, far exceeding the amounts in fermented foods, which contain hundreds of thousands to millions,” states Dr. Pojednic. “In this context, more is not better; natural sources provide a gentler, more physiologically effective way to support your microbiome.”

Another problem with probiotic supplements is they are created under the assumptions that the same bacteria strains are beneficial to everyone. But research indicates that microbiota composition and function varies significantly among individuals. What benefits one person may not necessarily work for another, and the scientific community is yet to develop the means to tailor probiotic prescriptions on an individual basis. Moreover, most beneficial gut bacteria that promote health are not yet available in probiotic supplement form.

“While healthy microbiomes may display certain shared characteristics, such as diversity, the specific types of bacteria that truly confer benefits remain unclear. Therefore, the limited selection of bacterial strains found in probiotic supplements may not be what your gut needs,” states Dr. Spencer.

Rather than taking probiotic supplements, Spencer and Pojednic recommend increasing the intake of probiotics by consuming fermented foods. Furthermore, fermented foods contain metabolic byproducts and other signaling molecules that probiotic supplements alone do not. Growing evidence suggests these metabolites confer additional health benefits and may aid the colonization of beneficial bacteria in our gut.

Fermented foods have been associated with enhancing microbiome diversity and overall health in several studies. A notable study was conducted at Stanford University, where participants adhered to a diet rich in fermented foods. Following a ten-week regimen of daily intake of five servings of fermented foods, participants demonstrated increased microbiota diversity and a notable reduction in inflammation in the body.

Dr. Spencer highlights this intriguing correlation, stating, “As the diversity of participants’ gut microbiome increased, there was a simultaneous decrease in various markers of inflammation, emphasizing the beneficial impact of fermented foods on overall health.”

“It’s important to remember that not all fermented foods have probiotic properties. When identifying probiotic foods, look on the labels for terms like ‘live cultures’ or ‘active cultures.’ Additionally, look for foods in the refrigerated section of the grocery store,” states Dr. Pojednic.

Should I Take Probiotics After Antibiotics?

A popular strategy to mitigate the depletion of one’s microbiota following antibiotics is to take probiotic supplements. However, a study revealed that probiotic supplements could unintentionally impede the normal recovery of the microbiota by displacing beneficial microbes in the gut. Participants who received the probiotic supplement took more than five months for their microbiome to recover, in contrast to those who received a placebo, whose microbiome returned to normal within three weeks. These findings suggest that taking probiotic supplements after antibiotic treatment did not help balance the microbiome; in fact, these supplements impaired its recovery.

“When this trial came out a few years ago, it created a paradigm shift in the field by showing that taking probiotics after antibiotics may actually delay the recovery of your microbiome,” states Dr. Spencer. “Now, I spend a lot of my time in GI clinics convincing people not to take probiotic supplements after antibiotics.”

While probiotic supplements are often used to alleviate symptoms linked to gastrointestinal conditions, such as irritable bowel syndrome and diarrhea, the American Gastroenterological Association does not recommend probiotics for the treatment of any adult gastrointestinal conditions outside of pouchitis. In any case, it’s advisable to consult with a physician before incorporating a probiotic supplement into one’s routine.

“As of now, there are very few probiotic supplements that have strong evidence of their beneficial effect in treating gastrointestinal disease,” states Dr. Spencer. “Nevertheless, this landscape is evolving quickly with ongoing research and advancements in probiotics. I’m hopeful that the next generation of probiotics will target GI disease more effectively.”

What Are Prebiotics and Why are They Important?

After establishing a diverse and healthy microbiome (by consuming a variety of probiotic foods), it becomes crucial to actively sustain it. What you eat directly fuels your microbiome community and determines which microbes will flourish and which will parish in the competitive landscape of your gut.

Prebiotics are nutrients that foster the growth and proliferation of beneficial bacteria in the gut, ultimately contributing to overall gut health. The main prebiotics our microbiome thrives on are known as microbiota-accessible carbohydrates (MACs), commonly referred to as dietary fiber. These complex carbohydrates, found in fruits, vegetables, whole grains, legumes, and other plant materials, resist our body’s degradation and absorption processes. This digestive resistance allows them to reach the colon still intact, providing a feast for our gut bacteria.

For individuals consuming diets high in sugar, fat, and protein, but lacking in dietary fiber, these macronutrients will break down and enter the bloodstream before reaching our colons. As a result, the typically diverse microbial community found in our colons will starve. Over time, the microbiome, in its quest for sustenance, may resort to consuming the gut’s protective mucus layer. This degradation can lead to a cascade of adverse effects, including inflammation within the gastrointestinal tract.

“Without the nourishment provided by fiber, the microbiome is left to fend for itself, potentially resulting in detrimental consequences for both its composition and the overall health of the gut,” states Dr. Spencer. “Eating prebiotic-containing foods is critical to sustain a healthy microbiome.”

In recent years, prebiotic supplements have gained popularity, however, our experts advise opting for fibrous foods over supplements to meet your microbiome’s probiotic requirements. This preference is rooted in the fact that foods offer a diverse array of fiber types, whereas supplements commonly feature a single type. The consumption of a singular fiber type restricts the nutritional support available to our microbiome, and can limit overall diversity that is crucial for a healthy microbiome. Moreover, fiber-rich foods offer various nutritional health benefits not found in supplements. Dr. Spencer suggests that if occasional supplement use is preferred to meet prebiotic needs, choosing supplements with a mix of fiber types is advisable. Nevertheless, opting for fiber-rich foods proves to be a more dependable and cost-effective source.

While more research is needed to fully understand the microbiome and how probiotics and prebiotics work in harmony, it’s reasonable to infer that the presence of one may enhance the function of the others. To promote microbiome diversity and a healthy gut, it’s essential for one’s diet to be a balanced combination of fermented foods (probiotics) and dietary fiber (prebiotics).

“My favorite breakfast is yogurt (a probiotic food) topped with berries and whole-grain granola (which are prebiotic foods). In one delicious meal, I fulfill all my biotic needs,” states Dr. Pojednic.

What Are Postbiotics and Why are They Important?

While many have heard of probiotics and prebiotics, the term postbiotics is relatively new. Postbiotics are the byproduct of probiotic and prebiotic activity. Essentially, they are the waste products left behind by the breakdown of fiber by the bacteria  in your microbiome.

These byproducts can be both beneficial and harmful to your health. The breakdown of fiber yields a treasure trove of beneficial postbiotics. Among these are essential elements such as vitamins, enzymes, amino acids, and short-chain fatty acids (SCFAs). One standout SCFA is butyrate, a superpower molecule throughout the body that plays a pivotal role in various aspects of health. Linked to a reduced risk of chronic diseases, butyrate also exhibits anti-inflammatory properties, supports brain health, and has beneficial metabolic effects.

Conversely, the breakdown of meat in the digestive process yields molecular byproducts such as choline and L-carnitine. In the microbiome, these compounds get broken down further into trimethylamine (TMA), which is subsequently absorbed by the circulatory system and oxidized in the liver to form trimethylamine N-oxide (TMAO). Elevated levels of TMAO have been associated with an increased risk of clot-related cardiovascular events. Intriguingly, a study conducted at Stanford suggests that refraining from meat consumption for eight weeks could potentially suppress the “bad” bacteria associated with TMA production when reintroducing meat into the diet, however, additional research is required to validate this hypothesis.

Postbiotic Supplements

While the concept of postbiotics is relatively new, the popularity of postbiotic supplements is on the rise. Butyrate supplements, for instance, are becoming increasingly common. It is essential to recognize that a deficiency in Butyrate might signify an underlying issue with one’s diet and digestive system, which a supplement alone may not rectify. The most effective strategy for boosting postbiotics involves embracing a diet rich in fermented food and fiber.

Take Home Message: Food is Better than Supplements

Compared to supplements, fermented and fibrous foods provide a diverse array of microorganisms that benefit your microbiome. Moreover, supplements miss out on the synergistic biotic combination of components found in whole meals. Research consistently underscores the pivotal role of diet in shaping the composition and function of a healthy gut microbiome, serving as the most comprehensive and research-backed biotic source.

“We have abundant data to demonstrate that food affects the microbiome. And while supplements certainly have their place–to address nutrient deficiencies and improve specific health outcomes–the evidence for the supplements widely marketed for benefiting the gut are limited at best,” states Dr. Pojednic. “To ensure your microbiome is getting the sustenance it needs, it is best to get your probiotics from fermented foods and prebiotics from high-fiber foods, which have the added bonus of numerous other health benefits.”

Another thing to consider is safety and efficacy of the supplements. Most supplements are loosely regulated by the FDA, meaning manufacturers don’t need to prove safety and efficacy. For this reason, it’s always better to get a nutrient or biotic source from food over supplementation unless it has been recommended by your physician or dietitian.

Most importantly, relying on biotic supplements cannot remedy the consequences of a poor diet. Long-term dietary habits play a pivotal role in the adaptability of the gut microbiome, with the consumption of diverse fermented and high-fiber foods being paramount. As our dietary habits evolve, so does the microbiome, adapting and diversifying to create a resilient and well-balanced ecosystem. In essence, the journey to a healthier gut extends beyond the allure of quick-fix supplements.

“While there is some regulation on manufacturing and marketing of supplements, enforcement is rare unless there is a well-documented negative health effect. Third party testing is key to ensuring you are consuming a safe product. Otherwise, you can fall prey to deceptive claims, mislabeled ingredients or possible contamination,” states Dr. Pojednic. “Safe, well studied supplements have their place, but we just aren’t there yet with these products.”

With ongoing advances in microbiome research, the future may hold more precise probiotic, prebiotic, and postbiotic interventions, potentially enhancing the effectiveness of supplements. However, the foundation of gut health remains deeply rooted in dietary habits, emphasizing the enduring value of natural, food-based approaches over supplementation.

Microbiome Expert Sean Spencer, MD, PhD: On a Mission to Prove that Food is Medicine

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By Sharon Brock, MEd, MS

Sean Spencer, MD, PhD is a Gastroenterologist and Physician Scientist at Stanford University School of Medicine. Along with seeing patients in the clinic, Spencer conducts cutting-edge research on the microbiome in the Sonnenburg Lab. In his research, Spencer focuses on how nutrition affects the microbiome and the immune system, as well as how our diet can prevent and treat gastrointestinal disease and potentially increase longevity.

“There’s a clear association between the microbiome and healthy aging. Studies of centenarians show a different microbiome configuration and metabolite production compared to those with a shorter life span and unhealthy aging,” says Spencer. “The microbiome is a key aspect of lifestyle medicine because what we eat and how we exercise affects our microbiome composition.” 

 The Medical Path

 Growing up amidst the rich agricultural tradition in Madison, Wisconsin, Spencer learned from an early age the importance of nutritious food for optimal health. As an undergraduate at the University of Wisconsin, Spencer majored in medical microbiology and immunology, and knew since his sophomore year that he wanted to practice medicine.

“After taking a human physiology course, I just knew that learning as much as I could about the human body and using that knowledge to help people was the only thing I wanted to do,” says Spencer. “As an undergrad, I also discovered that I could conduct research while caring for patients, and that clarified my career path further.”

These career goals prompted Spencer to pursue an MD-PhD program in immunology at the University of Pennsylvania, which he completed in 2015.

“In graduate school, I realized how our diet has a profound impact on the microbiome, and can directly influence the immune system,” says Spencer. “You want to think of the three aspects [nutrition, microbiome, and immune system] at the three corners of a triangle. They each impact the other.”

After completing an internal medicine residency at the Harvard-affiliated Massachusetts General Hospital, Spencer came to Stanford in 2017 for a fellowship in gastroenterology (GI).

“I came to Stanford specifically to work with Justin Sonnenburg, so it was great to be accepted to both the GI clinical program and his lab,” says Spencer. “What I love most about Stanford are the people and the creativity. This focus on the microbiome and nutrition is unique to Stanford and I’m glad to be part of a community that thinks about lifestyle medicine in both research and clinical care.”

Living His Dream

For the last three years, Spencer has been a practicing, board-certified GI physician at Stanford Medicine and a researcher in one of the most prestigious microbiome labs in the country. Spencer lights up when he talks about his current research on the small intestine microbiome:

“Most microbiome studies look at poop, which represents the very end of the GI tract, but the small intestine is 20 feet long, and researchers have sampled almost none of it,” says Spencer. “We’ve developed a novel technology to sample and investigate the microbiota [bacteria] of the small intestinal microbiome, which has been a huge blank space for the longest time.”

The small intestine is where many nutrients, including glucose, are absorbed into the bloodstream. Since high glucose levels are linked to diabetes and obesity, Spencer believes this research will potentially lead to the development of therapies to be used alongside lifestyle medicine, to enhance its benefits, for individuals with these medical conditions.

Spencer also studies hormones in the small intestine, such as Glucagon-like peptide-1 (GLP-1), which is the hormone targeted in the popular weight-loss drugs Ozempic and Wegovy. “The new GLP-1-targeted medications are powerful and amazing drugs, but it’s important to recognize that we have the power to regulate these hormonal pathways with our diet and lifestyle choices,” he says.

Although his work in the lab is a source of fulfillment, Spencer also enjoys bringing his research findings directly to his patients as a GI physician. Spencer is able to offer this bench-to-bedside level of care since he attained both a medical degree and a PhD in immunology.  

“I’m most proud that I have the skillset to listen to patients and identify what they need clinically, and then do the research to fill in the gaps and conduct clinical trials to develop new therapies to help them,” says Spencer.

Looking to the Future

Spencer’s future plans are to work in a clinical setting where he can continue to see GI patients and perform clinical trials on nutrition-microbiome-immune research. Studies from the Sonnenburg lab he would like to continue are testing the anti-inflammatory effects of fermented foods, which help treat food allergies, and the mechanisms by which our diet, microbiome, and immune system impact each other.

Regarding patient care, Spencer takes a “food is medicine” approach and plans to conduct more research to back up that message. “My future goal is to perform research that reinforces the recommendations of lifestyle medicine; to build the evidence-base for types of food that promote a healthy microbiome and prevent and treat disease,” says Spencer. “This research will help us understand what aspects of food are critical for promoting health and wellness and has real potential to offer improved dietary advice and to help our patients promote health through what they eat.”

Dr. Spencer’s Science-Based Smoothie for Gut Health

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By Maya Shetty, BS

In the complex world of gut health, finding straightforward solutions that effectively support the microbiome can be challenging. For this reason, Sean Spencer, MD, PhD, Gastroenterologist and Physician Scientist at Stanford University, created a meticulously engineered morning smoothie recipe to support his own gut health. Guided by his deep understanding of the gut’s delicate ecosystem, this smoothie is not just a meal but a strategic tool for fostering a flourishing microbiome.

Ingredients:

  • 1 cup spinach
  • ½ avocado
  • ½ apple
  • 1 tsp green banana flour
  • 1 tsp L-glutamine powder
  • 1 scoop (20 grams) pea protein powder
  • Top up with liquid of choice: water, coconut water, milk or nut milk (without additives)

Creating the Base

Dr. Spencer tailors his morning smoothie base with a focus on nutrient density and diversity, recommending a blend of apples, spinach, and avocado. Yet, he emphasizes the flexibility of the recipe to accommodate personal tastes and digestive responses. For those who find certain fruits, like apples, lead to bloating, Dr. Spencer says they can be easily substituted with other fruits like bananas or blueberries. 

“I find spinach, apple, and avocado make a tasty combination, yet the door is open to experiment with different fruits to achieve a healthy blend of nutrients and fiber,” he states.

Dr. Spencer points out the unique contribution of avocados to the smoothie. Unlike many fruits, avocados are rich in healthy fats, crucial for delivering steady energy throughout the day. Moreover, they are remarkably high in fiber, with half an avocado offering six to seven grams, making up about a quarter of the USDA’s daily recommended fiber intake. This dual benefit of avocados enhances the smoothie’s nutritional profile, making it a powerhouse of sustained energy and digestive health.

When it comes to liquid choices, almond milk is Dr. Spencer’s preferred option, but he notes the suitability of any type of milk or coconut water as long as it’s free from inflammatory additives, such as added sugars and thickeners, which can negatively impact the microbiome when consumed regularly. He also cautions against the deceptive practices of some brands that claim no added sugars while employing enzymes that convert complex carbohydrates into simple sugars (such as alpha-amylase added to oat milks), effectively sneaking in unwanted sugars.

“To ensure the healthiest choice for your microbiome, I recommend opting for products with short and simple ingredient lists,” he states.

Pea Protein Powder

Dr. Spencer chooses pea protein for its gentle impact on the digestive system and its impressive nutritional profile. It also boasts a comparable protein content to whey and includes all nine essential amino acids—vital nutrients your body is incapable of producing on its own.

Dr. Spencer advises that choosing the right protein powder for your gut is not about type, but rather additives. Most protein powders on the market, including pea protein, are formulated with emulsifiers. These additives, such as soy lecithin, cellulose gum, xanthan gum, guar gum, acacia gum, and polysorbate 80, are used to enhance the powder’s mixability in liquids. Despite their practical benefits, emulsifiers come with a downside–they’re notoriously harsh on the microbiome.

Recent research has shed light on the detrimental effects of common emulsifiers, revealing their capacity to directly alter the gut microbiota and incite inflammation. Such disruptions can compromise an otherwise healthy microbiome, underscoring the importance of choosing products wisely. A randomized controlled trial illuminated the extent of this impact, showing that the inclusion of emulsifiers in the diet over a mere 11-day period led to a noticeable decline in microbiome diversity and a reduction in the production of beneficial metabolic byproducts, or postbiotics.

Green Banana Flour (Resistant Starch)

Green banana flour enriches the microbiome with its high resistant starch content, a form of fiber with powerful benefits to the microbiome. Resistant starch has many health benefits and earns its name for its ability to bypass digestion in the small intestine, journeying instead to the large intestine. Here, it serves as a vital food source for beneficial gut bacteria, promoting a robust and healthy microbiome. The fermentation of resistant starch by these microbes results in the production of valuable postbiotics, such as short-chain fatty acids, essential for maintaining gut health. As bananas ripen they convert their starch to simple sugars, while the starch in green bananas remains intact, retaining its prebiotic properties. 

Dr. Spencer also mentions other fiber supplements like psyllium husk, which, although beneficial for digestion and adding moisture to bowel movements, does not serve as a fermentable food source for the microbiome. This distinction highlights the importance of choosing fibers that not only facilitate physical digestion but also actively contribute to the microbiome’s health.

“Other prebiotic supplements and sources exist. However, I choose to supplement with a resistant starch source because it has strong evidence that it is an accessible and fermentable source of fiber for microbiome,” he says.

While Dr. Spencer regularly uses green banana powder as a prebiotic supplement, he emphasizes the significance of incorporating a variety of fiber sources into one’s diet, noting this shouldn’t be the only fiber source in the day. 

“A diverse intake of fibers is crucial for a thriving microbiome, and I recommend consuming other prebiotic-rich foods such as potatoes, whole grains, beans, legumes, nuts, seeds, and a wide array of fruits and vegetables throughout the day,” he says.

L-Glutamine Powder

L-Glutamine offers a range of benefits for gut and microbiome health, such as reducing GI symptoms after morning workouts. It’s also recognized for its role in maintaining the integrity of the intestinal lining and reducing the inflammatory response during gut lining irritation. 

Furthermore, L-Glutamine serves as a vital energy source for the cells within the small intestine. This attribute is essential for maintaining intestinal health and addressing conditions where impaired intestinal barrier is present because it decreases gut permeability and reinforces the intestinal barrier.

 

More Than a Gut Feeling: How Your Microbiome Affects Your Mood

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By Maya Shetty, BS

Key Takeaways: 

  • The gut and brain are in constant communication through the gut-brain axis, which involves the nervous system, endocrine system, metabolic system, and immune system pathways.
  • Gut microbes produce neurotransmitters, hormones, and metabolites that can affect our emotions, thought processes, and behaviors.
  • Eating foods high in probiotics (such as fermented foods) and prebiotics (such as high-fiber foods) can improve the gut microbiome and mental health.
  • Processed food consumption negatively alters the gut microbiome, leading to adverse mental health effects via the gut-brain connection. 
  • In addition to diet, meditation and cognitive-behavioral therapy have shown to improve the gut microbiota composition, positively influencing the gut-brain axis.

When it comes to mood swings and mental state, the brain is often the first suspect. Yet, the trillions of microbes living in our gut, known as our microbiome, hold significant sway over our daily emotions and long-term mental health. This is because our microbiome and brain are in constant communication, influencing one another’s next move via the gut-brain axis.

“The complex interplay between our microbiome and brain is a testament to the body’s remarkable interconnectedness. It’s not just about gut health or mental health; it’s about how each influences the other in profound ways,” states Sean Spencer, MD, PhD, Gastroenterologist and Physician Scientist at Stanford University. 

The Gut-Brain Axis

The gut-brain axis represents a bidirectional communication system that intricately links the brain’s emotional and cognitive centers with the digestive system’s physiological processes. This complex network connects the central nervous system (CNS)—comprising the brain and spinal cord—and the enteric nervous system (ENS) within the gut using biochemical and physical pathways.

The ENS is an elaborate mesh-like system embedded in the gut lining, housing an astonishing 200 to 600 million neurons. Dubbed our “second brain,” this vast neural network, which spans from the esophagus to the rectum, contains many of the same structural elements as the brain.

“Our gut can be thought of as having its own brain, replete with motor neurons, sensory neurons, and neurotransmitters. In fact, our ‘gut brain’ contains more of some neurotransmitters, like serotonin, than the brain in our head,” states Dr. Spencer.

Instead of processing thoughts and emotions, our second brain focuses on orchestrating the digestion of food, absorption of nutrients, and intestinal motility (the movement of material from one end to the other). This unique system is equipped with its own reflexes and sensory capabilities, enabling it to adapt to the gut’s distinct conditions in real-time, independent from the brain’s oversight. In fact, studies have found the gut could still operate without direction from the brain. Under normal conditions, however, our gut and brain lean on each other to maintain homeostasis throughout the body using their intricate communication network.

The Vagus Nerve

The vagus nerve, one of the longest nerves in the body, forms the most direct link between the brain and the gut. It begins at the brainstem and stretches down to the abdomen, interfacing with various organs throughout its path. This nerve acts as a bidirectional channel, enabling the rapid exchange of signals from the brain to the gut and vice versa. 

Beyond the anatomical connection through the vagus nerve, the communication between the brain and gut includes endocrine (hormonal signals), metabolic, and immune routes. This continuous communication allows the brain and gut to be in sync. This expansive network highlights the gut-brain axis’s complexity, integrating diverse physiological signals to maintain mind and body balance.

The Microbiome’s Role in Mood

The key signaling molecules involved in the gut-brain axis are produced by the trillions of microbes making up our microbiome.  These microbes exist alongside the intestinal cells of the gut, which contain ENS neurons. This close proximity facilitates a dynamic exchange of signals between the microbes and the ENS neurons in the gut.

As research delves deeper into this symbiotic relationship, it has become apparent that our microbiome exerts a profound influence on the communication that flows through the gut-brain axis—so much so that it’s increasingly referred to as the microbiome-gut-brain axis. 

“Increasing evidence is showing that bacteria in the gut, and the byproducts they produce, affect mood, cognition, and behavior,” states Dr. Spencer.

Serotonin, Dopamine, and other Neurotransmitters

Neurotransmitters are crucial for communication within and between our brain and gut. Interestingly, the microbiome not only responds to neurotransmitters from the brain but also produces these same neurotransmitters that regulate thoughts and emotions, such as serotonin, dopamine, norepinephrine, and GABA.

“Serotonin, widely recognized for its role in mood regulation within the brain, also serves as a key signaling molecule in the gut. Remarkably, microbes in the gut are thought to be responsible for producing 95 percent of our body’s serotonin,” states Dr. Spencer.

Furthermore, the microbiome’s role extends to influencing neurotransmitter production throughout the body. Gut bacteria and our diet combine to provide and synthesize the tryptophan needed for serotonin production. 

“Variations in gut bacteria populations can alter the availability of tryptophan, impacting serotonin synthesis in the brain, which, in turn, influences our mood and behavior,” states Dr. Spencer.

Regulation of Hormones

The gut microbiome plays a pivotal role in regulating hormone secretion by gut cells, notably affecting hormones such as leptin, ghrelin, and insulin. These hormones are essential in communicating with the brain to regulate sensations of hunger and satiety and are also linked to influencing learning, memory, and emotions. Furthermore, the brain contributes to this dialogue by releasing hormones that modulate gut function, establishing a dynamic feedback loop between the brain and the gut.

Postbiotics

Postbiotics, the non-live byproducts of microbiota processes, are also integral to brain health. Microbial activity in the gut creates a variety of postbiotics, such as amino acids (the building blocks for neurotransmitters), glucose (which influences the brain’s energy metabolism), and fatty acids (which are crucial for brain development). These postbiotics serve as nutrients for the brain and are delivered from the gut to the brain through the bloodstream.

Recently, short-chain fatty acids (SCFAs), the primary metabolites derived from the microbial breakdown of dietary fiber, have garnered significant research interest for their wide-ranging positive impacts on brain health. SFCAs help strengthen the blood-brain barrier—a critical defense that shields the brain from potentially harmful substances while ensuring the smooth transit of vital nutrients— and exhibit powerful anti-inflammatory properties. These properties allow SCFAs to effectively modulate immune responses within the brain, significantly reducing neuroinflammation. Considering their comprehensive benefits, SCFAs are increasingly recognized as pivotal contributors to the dialogue within the microbiota-gut-brain axis, highlighting their vital role in supporting cognitive health.

Inflammation and Immune System

Gut microbes play a pivotal role in our body’s inflammation and immune responses, which directly impacts the integrity of the gut-brain axis. This communication network between our gut and brain is safeguarded by two critical barriers: the intestinal mucosal barrier and the blood-brain barrier. 

These barriers function as regulatory gatekeepers, managing the flow of information and maintaining the delicate balance within this network. Their permeability, however, is not static and can be influenced by various factors such as stress and inflammation, leading to fluctuations in gut-brain communication that depend heavily on an individual’s physiological state. As such, immune system activity in our gut has indirect, but significant, implications in the brain.

“An unbalanced immune response in the gut can increase the permeability of the intestinal lining—a condition commonly referred to as ‘leaky gut.’ This increased permeability allows substances that should remain within the confines of the digestive tract to enter the bloodstream and even to cross into the brain, potentially causing inflammation and contributing to the onset of various mood related  symptoms and conditions over time,” states Dr. Spencer. “I have seen the clinical implications of this in my patients, as those experiencing gut health issues are more likely to report low energy, brain fog, and anxiety.”

Nurturing the Gut for Better Mood

Research has revealed a complex network of bidirectional interactions linking the nervous system, the gut, and the microbiome. This dynamic interplay grants the microbiome a powerful influence over our psychological state. As a result, the health of our microbial community is recognized as a crucial factor in determining our daily mood and broader mental state. 

Dr. Spencer reinforces this connection by emphasizing the power of dietary choices: “Diet is the most modifiable and accessible way for people to promote a healthier microbiome.”

Diet plays a crucial role in shaping the composition and functionality of our gut microbiota. Consuming healthy foods fosters an environment where “good” microbes thrive, producing byproducts that benefit our mental health. Conversely, indulging in highly processed foods can tilt the balance in favor of “bad” microbes, leading to the production of inflammatory byproducts that negatively impact our mental well-being. As such, studies have focused on identifying dietary changes that can alleviate symptoms of depression, anxiety, and other mental health concerns. 

Observational studies have found that following a healthy, balanced diet, like the Mediterranean diet, as well as steering clear of pro-inflammatory foods and highly processed foods is linked to a reduced risk of depression. Randomized control trials have shed light on the advantages of consuming foods that positively affect microbiome health and composition. Following a “psychobiotic diet,” which focuses on prebiotic- and probiotic-rich foods and limits inflammatory items like sweets, fast food, and sugary drinks, has been linked to reduced perceived stress. Notably, greater adherence to this diet leads to more significant stress reduction. Prebiotic foods in this diet include fruits, vegetables, whole grains, and legumes, all high in soluble fiber, whereas probiotic foods consist of fermented items like kefir and yogurt. 

How Fiber Affects Mood

Another randomized control trial discovered that a high-prebiotic diet improved mood, anxiety, stress, and sleep in adults with moderate psychological distress. This diet involved consuming at least seven daily servings of soluble fiber-rich foods such as asparagus, garlic, onion, oats, whole wheat, and beans.

Interestingly, this study found that probiotic supplements did not yield mental health benefits, suggesting that the consumption of probiotic foods, rather than supplements, might be essential for mental health improvements. These studies highlight the potential of dietary interventions in enhancing mental health through gut-brain communication.

Considering the health of our microbiome requires not only focusing on what foods to incorporate into our diets but also which ones to avoid. Processed foods, a staple in Western diets for their convenience and taste, pose substantial risks to our microbiome’s environment. These items often contain heavily modified ingredients like added sugars, hydrogenated fats, processed meats, and artificial additives to enhance flavor and appearance. Common examples are sugary snacks, fast food such as burgers and fries, instant noodles, sodas, and pre-packaged meals. Consuming these items can disturb the balance of the gut microbiome, provoke inflammation, and adversely affect mental health via the gut-brain axis.

“I advise my patients to prioritize a diet high in whole foods and plants and to steer clear of processed and ultra-processed items, which are high in additives and preservatives that can disrupt the healthy bacteria in the gut,” states Dr. Spencer. “Moreover, I recommend dietary adjustments over the use of supplements like probiotics and prebiotics because food provides a necessary array of nutrients and fiber that currently available supplements cannot yet replicate.”

While the connection between diet and mental health is compelling, it’s important to recognize that food should not be seen as the sole treatment for mood disorders. Especially in cases of severe depression and suicidal thoughts, professional medical advice and treatment are paramount. Diet can play a supportive role in managing mild to moderate forms of depression and anxiety, complementing traditional treatment methods and contributing to overall mental health resilience.

Nurturing the Brain for Better Gut Health

While the microbiome plays a crucial role in shaping our daily mood and overall mental health, conversely, the brian profoundly influences both the composition and functionality of our microbial communities.

Decades of evidence have demonstrated how stress negatively impacts the gut microbiome, both directly affecting the gut microbiota and indirectly altering the gut environment. This is in large part due to the connections between the CNS and ENS, where activation in one system can trigger responses in the other. 

Excessive stress impacts gut transit and motility, leading to reduced nutrient delivery to the microbiome and consequently affecting its growth and diversity. Additionally, stress can impair the secretion of mucus by gut cells, weakening the intestinal mucosal barrier that protects our microbiome. Even short-term stress has the power to significantly alter the microbial community composition, diminishing both its diversity and population.

Improvements at the brain level, such as through cognitive-behavioral therapy (CBT) or meditation, can positively influence gut-microbial composition and function. A study involving participants with Irritable Bowel Syndrome who underwent CBT not only noted changes in brain activity but also observed alterations in the relative abundances of gut microbes. The specific CBT approach taught patients informational processing skills, fostering more flexible thinking about situations and reducing stress.

Similarly, another study explored the potential influence of long-term, regular meditation on the gut microbiota. Participants who practiced meditation exhibited distinct changes in the composition of their gut microbiota compared to a control group, suggesting that mindfulness practices can have a beneficial impact on gut health.

Despite the growing understanding of the gut-brain-microbiome axis, researchers face challenges in studying the relationship between mood and the microbiome due to the myriad of factors involved. The complexity of the microbiome and its sensitivity to a wide range of influences, including diet and stress levels, make it difficult to isolate specific effects on mood. However, the accumulating evidence highlights the promising potential of interventions designed to mitigate stress and enhance mental health. These strategies not only positively influence the gut microbiome but also open novel pathways for addressing gastrointestinal and psychiatric disorders, as well as improving overall mood.

“I’m confident that in the near future we will gain a far more clear understanding of how our diet and microbiome influence our mood,” states Dr. Spencer. “As this field of research expands, we will likely see more ‘psychobiotics’, which are targeted microbial therapeutics to improve our gut-brain connection. Dietary and microbial approaches to improve mental health will undoubtedly be part of our toolkit to promote well being.”