Food for Thought: The Secret Power of Your Gut for Mental Wellness and Preventing Disease

By Dominique Thomas, Alliance Intern from University of Alabama at Birmingham ‘24

It’s lunchtime. You grab a veggie-loaded sandwich and some fruit and end the hour much more satisfied than when it began. And now, the journey of those swallowed bites begins – down the esophagus, sloshed and churned in the stomach, slowly absorbed and pushed through the intestines and purged. For some, this is the extent of knowledge surrounding the digestion system, and for many, this knowledge is joined with the understanding that eating healthy is important for good health, but why is this?

Often overlooked and under-appreciated, the gut and its digestive partners are proving to be the key to overall health and alleviating numerous health struggles, even solving medical mysteries. The recently released Netflix documentary, Hack Your Health: The Secret of Your Gut, is a great introduction to the concept of gut health. Science experts from around the globe share their insights and research about the microbiome and gut health. By watching, you quickly learn they all share the same sentiment – gut health is imperative to overall health.

Creating and Maintaining a Happy Gut Microbiome

Giulia Enders, an MD and the author of Gut, compares the gut to a forest, full of living organisms that depend on each other and good conditions to thrive. “You can’t put a few healthy plants in it and expect everything to change,” she says, “a forest needs a healthy balance.” This is true for the gut as well; a few healthy meals cannot maintain a healthy gut or a diverse microbiome, but many healthy meals will do just that.

Composed of all of the microscopic life inside and on the surface of the body, the microbiome is the foundation for many bodily functions. Much like insects in the forest working to keep the ecosystem stable, the bacteria, fungi and viruses of our microbiome all work to keep our body functioning and healthy.

This is especially true in our guts, where Healthline says approximately 40 trillion helpful microbes live (vastly outnumbering the 30 trillion human cells we have in our bodies). These microbes are responsible for the breakdown of food and absorbing the nutrients it contains. In this process, not all foods are equal. Highly processed foods, like chips and cakes, are digested very quickly. While natural foods, like fruits and vegetables, are digested much more slowly. Enders compares this to the difference between a sprint and a marathon.

The high-sugar, low-nutrient foods may be absorbed as early in the digestive tract as the stomach. The quick absorption spikes blood sugar levels and elicits a stressful reaction from your cells. Mainly eating foods of this nature result in chronic inflammation in the gut, which “can lead to conditions such as arthritis, heart disease, stroke, and diabetes,” and other chronic diseases, shares Cleveland Clinic.

Contrarily, the natural, fiber-dense foods are slowly absorbed by the microbes throughout your entire system (and even reach your large intestine!). This fiber comes from the fruits, vegetables, legumes, nuts and seeds we eat. By eating these foods, you can decrease inflammation in the gut and body and support your microbiome. This keeps your microbiome happy, which in turn keeps it diverse and populated.

A happy, populated microbiome is very important, as our microbiomes influence many things and are “very central to being obese, being depressed, having allergies, or how stressed or relaxed you’ll feel,” says Enders. “We don’t know how big the part that it plays in these entities is.” For some, the microbiome may be the biggest influencer, and for others, it may be a much smaller fraction of a particular condition’s cause.

Everyone’s Microbiome is Incredibly Unique

The microbiome is formed through every event and action of a person’s life. When a baby is born vaginally, they are exposed to their mother’s vaginal microbes. An exposure that is increased exponentially when the head exits the canal, right next to the mother’s butthole. Here, the baby is introduced to another round of microbes. This begins the gut’s colonization. Microbes continue to be introduced to infant guts through breastfeeding and exposure to different environments, people and pets.

Where you live, who you kiss or drink after and of course, what you eat, are all things that determine what microbes live in your gut – which in turn influence your brain, gut and overall health. The more diverse the microbial collection, the healthier the microbiome. A healthy microbiome is able to digest a wide variety of foods because it has been built by slowly evolving the diet to include as many foods as possible. Opposingly, an unhealthy microbiome comes from the limitation of foods and often leads to difficulty in digestion. 

The Challenges with SAD (the Standard American Diet)

Justin Sonnenburg, a microbiologist and professor at Stanford, says that experts in his field are “realizing now that the most important factors of determining the health of this microbial community is your diet,” which is what makes eating an arrangement of fruits, vegetables, beans, nuts and seeds so important. Because of our current diets, “we’ve lost hundreds of species in our gut,” he says “they’ve gone extinct,” which has caused our gut health to decline and be less diverse.

These less diverse microbiomes have become known as industrialized microbiomes, a product of “big changes to our environment, Western diet, the way babies are born, C-sections, baby formula, sanitation and antibiotics,” Sonnenburg says.

Food manufacturers strip food of its nutrients – replacing it with sugars, fats, sodium and chemicals during processing – denying microbes in the intestines nutrients, resulting in decreased counts of microbes. Antibiotic prescriptions, often given without instructions to take with prebiotics and probiotics, wipe out microbes at high rates and leave the microbiome barren.

Sonnenburg shares that these behaviors, paired with the changes mentioned above, “all lead to decreased microbiome diversity.” This is “exactly what we see in the industrialized microbiome” which is becoming more common, especially in developed nations like the United States.

“There are some major deficiencies in the typical American diet,” he says, even in an “American diet that’s healthy.” Which is putting it mildly. The Standard American Diet, which consists of “50% carbohydrates, 15% protein, and 35% fat,” according to this Fullscript article, is often void of the fiber-rich foods recommended. Instead, it is composed almost entirely of foods like refined grains, fried foods, sugary beverages and ultra-processed foods – all hefty contributors to the industrialized microbiome.

The Brain and Gut Are BFFs and Their Connection to Depression

Annie Gupta, a neuropsychologist at UCLA, says to “think of the brain and the gut as BFFs.” Like best friends, the brain and gut depend on each other for many things. “So, if either one is not working, the other eventually is gonna follow suit.” This is why when certain bacteria are introduced back into the gut, symptoms of psychological and neurological illnesses can be alleviated, and why eating a poor diet often leads to declines in mental health.

“The beautiful thing about the microbiome is it’s everywhere, and its effects are felt everywhere,” praises microbial ecology researcher Jack Gilbert. Through data gathered from stool samples, Gilbert has established ties between the microbiome and many health conditions. He shares that he and his team have “found that people with certain depression-like symptoms are missing bacteria in their gut that produce chemicals which shape brain chemistry.” When these bacteria are reintroduced to the microbiome, the depression-like symptoms are minimized and may even disappear entirely.

Our Two Brains and Their Connection — The Need for a New Whole Body View

Another important take is given by John Cryan, a neuroscience professor at University Cork College. He shares that we have two brains, one in our heads and one “within our tummies,” connected through the “gut-brain axis.” He explains this as, “the two-way street of communication between what’s going on in our bellies and what’s going on in our brains.” Cryan’s research recognizes that “co-occurrences of gut problems with brain problems” are “very common in autism, in Parkinson’s disease … high stress-related psychiatric illness like anxiety and depression,” and further proves the need to understand the mind-gut relationship.

Both believe the body needs to start being analyzed as a whole. Gilbert states, “Our study of the body as a whole unit is essential if we’re really gonna get a handle on some of these chronic diseases,” like obesity, diabetes, and even allergies. Cryan says, “We have to think more holistically” about our health. Doctors and researchers have to stop ignoring the relationships between the gut and the mind to care for their patients. As more research is published, one thing is made clear — ignoring the mind-gut connection is impossible and, frankly, unethical.

“70% of Our Immune System Lives in Our Gut”

The connections between neurological syndromes, chronic diseases, allergies and the gut are more easily believed after hearing Sonnenburg say that “approximately 70% of our immune system lives in our gut” and is trained by our microbes to “respond to bad organisms that might have a consequence on health.” This is one of the biggest reasons to foster a diverse collection of microbes in your gut: the richer the microbiome, the more bacteria for your immune system to learn from.

Tim Spector, an MD and genetic epidemiologist, says this richness and training is what “allows you to deal with allergies and intolerances better.” Because the diversity exposes your immune system to more, which prepares it to fight infection better, feeding our guts a wide range of foods is one of the biggest ways to improve our immune system. Sonnenburg adds it also often helps “to quiet inflammation and make the immune system less likely to cause autoimmune disease.”

Improving Your Own Gut Health With a Diversified Microbiome

“Knowing that the microbiome could be the key to health is really exciting,” Spector says, “because you can’t change your genes, but all of us have the ability to change our own microbes.” As inspiring as that may sound, how do we do it?

Because there is no “standard microbiome,” there is also no standard, one-size-fits-all method for repairing or improving one. And while there are ways to introduce more microbes to your body and improve your gut health, it is important to remember these changes cannot be rushed. Developing a diverse microbiome takes time, dedication and patience.

While improvement to the microbiome can be seen as early as 1 week. Gilbert shares that it may take up to “9 to 12 months to reshape the ecosystem,” for those that suffer from chronic digestive conditions like inflammatory bowel disease or irritable bowel syndrome, so it is important to keep going and making improvements for a longer time.

Microbiome reshaping comes from eating diverse, healthy foods and not just low-carb, low-sugar, fad diets. Ideally, you would include 50 grams of plant fiber a day, the new amount recommended by the field of microbe science. This would come from fruits, vegetables, legumes, nuts and seeds.