Trillions of microscopic organisms live inside our bodies. They’re concentrated in our digestive system, especially in the large intestine, where they help break down the food we eat.

But that’s only the beginning of the story. A growing body of research reveals that those microbes have far-reaching effects. In fact, the gut microbiome has a powerful influence on how much we weigh, what foods we crave, how we feel and even how our minds work.

Reset explores the mind-gut connection with UChicago Medicine psychogastroenterologist Alyse Bedell.

What is the gut microbiome?

The human gut is home to trillions of bacteria, viruses, fungi, parasites and other microorganisms. Around 5,000 species in all. Many of them are beneficial and play key roles in the digestive, endocrine, immune and nervous systems. Others can make us sick.

Like a forest or a coral reef, a gut microbiome is an ecosystem. It’s constantly in flux based in part on what a person eats, and it’s constantly in touch with other parts of the body, including the brain. What happens in the brain and mind affects the gut. And vice versa.

“This is a bi-directional, two-way street,” Bedell says.

Each person, by the way, has a unique gut microbiome influenced by their genes, environment, diet and other factors.

How does the mind-gut connection work?

It’s easy to understand how our thoughts affect our gut. Just think of the phrases “butterflies in the stomach” or “a punch to the gut.”

“Those are figures of speech for a reason because we actually have that experience of stress that manifests in our body,” she says. “Our GI tract is intricately involved.”

It’s when influence moves in the opposite direction — from the gut microbiome to the brain — that we need a bit more explanation. Here are some examples.

• If you eat a lot of leafy greens, the microbes in your gut that prefer them over, say, cheeseburgers, will multiply. And that will make you crave leafy greens more often.

• Some bacteria in the gut synthesize neurotransmitters like serotonin, dopamine and GABA, and that synthesis shapes our moods and emotions.

• A 2018 study suggests the interaction between gut bacteria and the brain can shape structures in the brain responsible for learning and cell growth.

In her work as a therapist, Bedell says she often sees patients affected by the mind, the gut or both.

“Some of the most common times that people might present for treatment is after a loss, after a breakup, or conversely, it might be after a horrible bout of gastroenteritis,” Bedell says.

How can we foster a productive gut microbiome and mind-gut health?

Eating a nutritious diet will have an impact on both your physical health and mental health.

Beyond that, if you notice something off with your gut, Bedell says don’t ignore it.

She recommends consulting with a gastroenterologist, especially one who is part of a multidisciplinary team that includes a GI specialist, a dietitian and a psychologist who has expertise with GI conditions.

In some cases, experts may prescribe cognitive behavioral therapy or gut-directed hypnotherapy to help ease a condition, Bedell says.

On the flip side, it’s crucial to pay attention to your mental health. Anxiety, depression, chronic stress and other issues often affect the gut microbiome and lead to symptoms in the gut.

“If you’re only working on the gut, you’re really just working with one half of that important puzzle,” she says.

Reset host Sasha-Ann Simons spoke with Alyse Bedell, an assistant professor of psychiatry, behavioral neuroscience and medicine at UChicago Medicine.

You can listen to the full conversation above.