The Connection Between Gut Health and Depression

By Laura Rodriguez, Spoon University

In the world of medicine and nutrition, there’s been a lot of buzz about the connection between gut health and mental disorders over the past several years. As a health junkie and nutrition enthusiast, I was hearing about this constantly, so I decided to delve into the deep and complex subject that is our gut health and the microbiota, and just how it is that our brain is involved in all this because – I gotta admit – I’m a kind of a nerd when it comes to evidence-based nutrition.

Multiple studies and scientific articles now relate a variety of both mental and physical diseases to specific kinds of bacteria – or lack thereof – that call our gastrointestinal (GI) tract home. If you want to know how the countless microbes that line our gut and body play a big role in how we feel both physically and emotionally, you’ll find all the info down below.

What Is The Gut Microbiota?

Our microbiota is made up of 10-100 trillion microbial cells located all over our body, but primarily in our GI tract, better known as our gut. The term microbiota is used to refer to the microbial species that live on or inside of us, whereas the term microbiome also includes the genes in the bacterial cells. Yes, bacteria have their own set of genes.

More fun facts on the microbiota: for every human cell there are 10 microbial cells, and for every human gene, there are 100 microbial genes. So we’re basically more bacteria than human. Literally. This is precisely why it’s estimated that up to 90% of diseases can be in some way traced back to a disturbed microbiome.

The Gut-Brain Axis

The link between our gut health and our brain has become an actual scientific term, given the wide evidence that suggests the systemic communication between our central nervous system and gut microbiota.

It’s well documented that “Hormones, neurotransmitters and immunological factors released from the gut are known to send signals to the brain either directly or via autonomic neurons.” This is also why antidepressants are a common pharmaceutical intervention for irritable bowel syndrome, and why a great number of GI patients also suffer from mood disorders, and conversely why psychiatric patients often have GI problems.

How Does My Gut Health Affect My State Of Mind?

Our gut microbiome is in charge of the secretion of short-chain fatty acids, hormones, and neurotransmitters, all of which contribute to proper brain function.

In an interview with Paulina Ortiz Roel, graduate of Universidad de Monterrey (UDEM) with a degree in Nutrition, and expert in all things microbiome, she said, “In the case of depression, it’s well known that there are certain types of bacteria that participate in the secretion of serotonin,” which is a neurotransmitter that makes us happy. A person with depression probably doesn’t get the “happy signal” to their brain because they lack the bacteria responsible for secreting serotonin.

Our gut bacteria creates 95% of our body’s serotonin. If those little guys aren’t in our favor, our feelings of happiness can be compromised.

There seems to be a parallel between gut dysbiosis and psychiatric conditions such as chronic depression and even schizophrenia. Antibiotic exposure – especially early in life – in addition to a high-fat diet can promote “pro-inflammatory bacterial metabolites”. When we undergo antibiotic treatment, the bacteria-killers can’t tell the difference between good bacteria or bad bacteria, so they go ahead and wipe us all out, depleting us of the good guys in the gut that take care of our brain, mood, weight, and immune function, which leaves us more susceptible to infection.

The gut and brain have a symbiotic relationship, where one affects the other equally. “SCFAs, produced by the bacterial fermentation of dietary carbohydrates, have immunomodulatory properties and can interact with nerve cells by stimulating the sympathetic and autonomic nervous system via G-protein-coupled (GPR) receptor 41 (GPR41).” Translation: the production of short-chain fatty acids that comes from quality carbohydrate consumption is good for our nervous system.

Does What I Eat Matter?

To put it briefly, yes. When you eat, you’re not only feeding yourself, but you’re also feeding the bacteria living in your gut. For instance, if you eat sugar all the time, you’re feeding the sugar-loving bacteria, making them proliferate, which in turn increases sugar cravings. There’s a reason why snacking on donuts and cookies all the time won’t make you crave apples and kale. However, if you snack on fiber-rich fruits and veggies, nuts, and whole grains, your body (or should I say bacteria?) will definitely be asking you to keep those green smoothies coming.

If you want to know what eating junk food consistently does to your gut, check this out. This kind of damage has serious physiological implications. Not only is your physical health at risk, but this study concludes that these types of dietary patterns can actually lead to depression. This is because calorie-dense and nutrient and fiber-poor foods can cause an overgrowth in the bad type of bacteria, along with the systemic death of good bacterial strains. As said in this article, “Diet is another important determinant of gut microbiota composition and function that is strongly linked with psychopathological outcomes.”

Paulina mentions that despite the fact that a high-protein diet can be effective for weight loss, “it makes substantial changes in the microbiota, given there are now more bacteria that ferment protein. In that fermentation, there are good byproducts, but there are also bad byproducts which, in the long-term, can lead to disease.” It turns out that the diet that may be giving you major gains at the gym could possibly cause complications in the long-run, both physically and mentally.

Think adding Splenda to sweeten your drinks is a health habit? You might want to reconsider that, given Paulina talked about how “Artificial sweeteners act as antibiotics. It has been studied that in a matter of weeks [of frequent consumption] there can be severe changes in the microbiota,” as seen in this article and this study.

Unfortunately, we can’t outsmart our body’s sweetness-receptors with Splenda (or any sweetener that contains sucralose, saccharin, or aspartame, to name a few). If, however, you can’t stand the taste of your morning coffee solo, consider adding pure stevia extract (in the form of drops or green powder, which is ground stevia leaves), or honey, agave nectar, or brown sugar in moderate quantities. Or, better yet, you could try to cut down on how much you sweeten your food and beverages. You’d be surprised at how quickly our taste-buds (and microbes) adapt to a lightly sweetened lifestyle.

What Can I Do To Improve My Gut Health?

Eat more fiber! Experts corroborate on the fact that complex, non-refined carbs are the preferred food of our gut bacteria, providing them with the most nutrients for optimal development. This is because fiber is a prebiotic, which is what our bacteria eat to multiply and improve our health.

I’m sure we’ve all heard at some point that fiber is indigestible right? Well, it doesn’t just sit there in our GI tract; even though we don’t actually digest it, our gut microbes feast on it. Cool huh? In other words, “the fiber fermentation process in the colon promotes bacterial growth.” Sources of prebiotics include fruits, vegetables, nuts, seeds, whole grains, and legumes. Basically, unprocessed foods of plant-origin are your gut’s best friend.

Also, apple cider vinegar (with The Mother – the prebiotic fiber) “create[s] a certain type of pH in your body that supports the growth of probiotics in your system.” Drink 1-2 tablespoons of this diluted in a glass of water regularly to promote healthy bacteria growth.

Now that we’ve mentioned prebiotics (what our bacteria eat) let’s talk about probiotics and fermented foods. Probiotics are actual living bacteria that can colonize and diversify our gut microbiota, improving the “body’s ability to absorb nutrients and fight infection.” The consumption of probiotics in the form of capsules, powders, or fermented foods (sauerkraut, kimichi, kefir, yogurt, kombucha, miso, tempeh) is highly beneficial for optimal microbiome function. So sipping your favorite kombucha is not only delicious and refreshing, but it’s giving your gut health a major boost.

As Paulina states, “What’s best for the microbiota is a Mediterranean diet: rich in legumes, fiber, vegetables, fruit, and moderate in protein,” Basically a diet that is mostly centered around whole plant foods with lots of fiber, healthy fats, and with minimally processed foods, no trans fat, and limited in animal protein (if consumed, make sure it’s not conventional, always grass-fed, and not treated with added hormones or antibiotics, given antibiotic residues in animal tissues can have also have detrimental gut microbiota effects and excess hormonesin our body can make our endocrine system go haywire).

Paulina also highly recommends adding fermented foods into our daily diets to increase our microbial diversity and ward off disease. For more gut-friendly advice, make sure to follow her on Instagram @nutritionforguthealth.

Photo courtesy of Paulina Ortiz Roel

Also, as world-renowned gastroenterologist and microbiome know-it-all Dr. Robynne Chutkan says, “live dirty, eat clean.” Skip the Purell and other anti-bacterial products – plain soap and warm water will do. Go outside, get your hands dirty – literally. Interacting with microbes familiarizes our immune system with them and makes us less susceptible to infection, in addition to diversifying our microbiome, further protecting us from mental illnesses as well.

In her interview on the Rich Roll Podcast, Dr. Chutkan talks about the hygiene hypothesis and how our obsession with sanitizing everything and overuse of antibiotics has led to a world of autoimmune, infectious, and chronic diseases. So don’t be afraid of a little dirt now and then; it does more good than harm.

Now that you have a sense of what depressive behaviors can be interpreted as in terms of gut microbiota health and the factors that can interfere with a healthy microbiome, you can try to implement small lifestyle changes that can potentially turn your gut health around.

The wellbeing of our gut microbiota dictates not only our digestive patterns and immune system function, but also how we feel on an emotional level. Who knew a simple thing such as adding sauerkraut to your favorite foods can help colonize your gut and provide overall health, (apart from tangy deliciousness)?

Even though depression is a complex mental disorder that has many contributory factors, keeping your little guys in the gut happy and well-fed can have beneficial effects towards brain health and overall wellbeing.

This article is not intended to serve as medical advice and does not substitute professional medical recommendations imparted by a physician or psychiatrist.

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