The Gut-Brain Connection: How Stress and Gut Health Affect Each Other

Almost everyone has felt the gut-brain connection: butterflies before a big moment, a nervous stomach before a presentation, losing your appetite when you're upset. But the connection runs much deeper than that, and it runs in both directions.

When people come to me with brain fog, anxiety or mood issues, gut health is one of the root causes I look at. Honestly, it's hard to say which comes first. Stress is at the root of just about everything, and a struggling gut is itself a source of stress. Stress and gut health aren't the only foundations of health, but they sit at the root of so many of the conditions I see.

In this article, I'll explain how the gut and brain talk to each other, why stress shows up in your stomach, how an unhealthy gut can affect your mood and energy, and the practical steps I use to support both sides.

In this article 7 sections

What Is the Gut-Brain Connection?

The gut-brain connection, often called the gut-brain axis, is the communication network between your digestive tract and your brain. It works through several channels at once:

• The vagus nerve. A long nerve running from the brainstem to the gut, carrying signals in both directions.

• Stress hormones. Cortisol and related hormones change how your gut moves, secretes and protects itself.

• The immune system. Much of your immune activity sits along the gut lining, and inflammation there can affect how you feel overall.

• Chemicals made with the help of gut bacteria. Your microbes help produce or regulate compounds that act on your nervous system.

Animal research gives a sense of how direct this can be. In mice, feeding a specific probiotic strain reduced anxiety- and depression-like behavior and lowered stress hormones, but the effect disappeared when the vagus nerve was cut [4]. Mouse studies don't translate neatly to people, but they show the gut and brain are wired together.

How Stress Shows Up in Your Stomach

If you've ever had a stress stomach ache or a nervous stomach, you've felt the brain-to-gut direction. Your gut works best in rest-and-digest mode. When you're stressed, your body shifts into fight or flight, and digestion moves to the bottom of the list. That can mean:

• Cramping, a knotted or nervous stomach, or nausea

• Bloating, even after normal meals

• Diarrhea, or the opposite, constipation

• Heartburn or feeling heavy after eating

• Loss of appetite, or cravings for sugar and comfort food

Stress can also affect the gut lining itself. In a study of healthy volunteers, the stress of giving a public speech increased small intestinal permeability, and only in people whose cortisol rose [2]. In other words, stress alone can make the gut lining leakier, at least temporarily.

Can stress cause stomach problems? Yes, and it's one of the most direct drivers of poor gut health I know of. But if your symptoms are persistent, don't assume it's "just stress." It's rarely one thing, and other causes are worth ruling out. Our guide to why you might always be bloated walks through the common ones.

How Your Gut Affects Your Mood, Energy and Focus

Serotonin starts in the gut

Most people think of serotonin as a brain chemical, but an estimated 90% of the body's serotonin is made in the digestive tract. Research in mice found that gut bacteria help drive that production: without their normal microbes, the gut cells that make serotonin produced about 60% less of it [1]. Gut serotonin doesn't simply travel to the brain, but it shows how much your microbes influence the chemistry of your whole body.

Your body runs on precursors

One of the things Richard Helfrich, our co-founder, has taught me is that the body always runs on precursors. That's why we generally prefer to give the body the building blocks it needs rather than the finished product. But your gut bacteria are a big part of turning those building blocks into the finished compounds your body uses, including neurotransmitters and important cofactors and nutrients.

So when your gut bacteria are out of balance, a state called dysbiosis, that process breaks down. Instead of producing what your body needs, you end up bloated, in pain, sluggish and tired. And feeling that way day after day is going to drag down your mood and feed anxiety and depression.

Research is starting to back up the connection. In a study of more than 2,000 adults, two groups of gut bacteria, Coprococcus and Dialister, were consistently lower in people with depression [3]. That shows an association, not that the bacteria cause depression, and it may run both ways, which is exactly the chicken-and-egg problem.

Running on empty

Something I've noticed with anxiety is how often it shows up when people are trying to do something they don't have the energy for. If you're pushing through a very intense job several days in a row while you're exhausted, you're going to feel stressed, flat and depressed. And if your gut isn't digesting and absorbing well, you're running on even less fuel to begin with. There's a direct connection there.

Physical Stress Counts Too

We usually think of stress as emotional: work, money, relationships. But there are physical stressors too, and in my experience they can sometimes be even more taxing on the brain than emotional ones.

• Overgrowths and parasites. A significant bacterial or fungal overgrowth, or picking up a parasite, puts real, ongoing stress on the body. See our guides to SIBO and parasite symptoms in adults.

• Mycotoxins. Toxins from mold affect the gut, but they can also build up in other places in the body. More in our guide to mycotoxin testing.

• Lifestyle choices. Say you have a stressful week at work, so you go out and drink with friends. You wake up the next day with your liver overloaded, and now you have physical stress stacked on top of emotional stress.

That's why I don't look at mood in isolation. If you've been dealing with brain fog or anxiety alongside gut symptoms, it's worth testing rather than guessing, ideally with a practitioner.

How to Support Your Gut-Brain Connection

1. Eat in rest-and-digest mode

You can't digest well when you're stressed. Eating a burrito while driving and talking on the phone is about the worst thing you can do for your gut. Sit down, take a few breaths before your first bite and be present with your food. One of my favorite authors, Thich Nhat Hanh, wrote a small book called How to Eat about exactly this.

2. Build small daily rituals

A few minutes of meditation and some sunlight before work, and a walk without your phone when you feel anxious, go a long way. Our simple breathing practice is an easy place to start.

3. Protect your sleep

The biggest sleep mistake I see is blue light at night. Cut screens around 8 p.m., use blue blockers if you need to, and start an unwind routine so your cortisol can come down and your brain can make its own melatonin.

4. Don't eat on the run, and don't overdo it

Don't take your digestion for granted. Digestion takes hours for some foods. People on the go take a handful of vitamins, eat fast and assume they're absorbing everything. Give your gut the time it needs.

5. Feed the gut terrain

Cut back on constant high-glycemic foods, high-fructose corn syrup and sugar-loaded smoothies. Make half your plate vegetables, add bitter greens, and drink good spring or mineral-rich water. If certain foods seem to set you off, a structured elimination diet can help you find them. Keep things moving too, since constipation adds its own load on the body.

6. Support your microbiome

A healthy microbiome comes down mostly to diet and stress management. When you add a probiotic, it doesn't need to be complicated: specific strains that colonize the gut, in an enteric-coated, shelf-stable capsule. Our Multi-Strain Probiotic Complex has eight strains in that format.† Short-chain fatty acids like butyrate matter too, since they fuel the gut lining; our Butyric Acid can help while you rebuild, and our butyric acid guide covers the foods that support it.†

7. Support your stress response

Lifestyle comes first, but some people need extra support while they rebuild. Our Adrenal Calm & Restore is a liposomal ashwagandha tonic made to support your body's stress response.† More on the stress side in our guides to how stress affects your body and how to lower cortisol.

When to See a Doctor

Talk to a doctor or mental health professional if anxiety, low mood or brain fog is affecting your daily life, or if you have thoughts of harming yourself. See a doctor promptly for digestive warning signs like blood in your stool, unexplained weight loss, persistent vomiting or symptoms that wake you up at night. Supporting your gut can be a helpful part of the picture, but it isn't a replacement for medical or mental health care.

The Bottom Line

Your gut and brain are in constant conversation. Stress shows up in your stomach, and a struggling gut can show up as anxiety, low mood, fatigue and brain fog. Since it's hard to know which came first, work on both: manage stress, eat in rest-and-digest mode, protect your sleep and build a healthy gut terrain. And remember that physical stressors, like overgrowths, mycotoxins and a hard week of drinking, count too.

References

1. Yano JM, Yu K, Donaldson GP, et al. Indigenous bacteria from the gut microbiota regulate host serotonin biosynthesis. Cell. 2015;161(2):264. PMID 25860609

2. Vanuytsel T, van Wanrooy S, Vanheel H, et al. Psychological stress and corticotropin-releasing hormone increase intestinal permeability in humans by a mast cell-dependent mechanism. Gut. 2014;63(8):1293. PMID 24153250

3. Valles-Colomer M, et al. The neuroactive potential of the human gut microbiota in quality of life and depression. Nat Microbiol. 2019. doi:10.1038/s41564-018-0337-x

4. Bravo JA, Forsythe P, Chew MV, et al. Ingestion of Lactobacillus strain regulates emotional behavior and central GABA receptor expression in a mouse via the vagus nerve. Proc Natl Acad Sci USA. 2011;108(38):16050–16055. PMID 21876150