A doctor says looking after your gut will take care of your brain and immune system, too. Here are 3 things he does himself, including 'gut gardening.'

• The evidence that gut health affects our overall health is growing. 
• Dr. Monty Lyman explained that growing evidence suggests the brain, gut, and immune system are linked.
• He shared what he does to nurture his gut health, including making his own sauerkraut.

Growing research on the trillions of microbes that make up what's known as our gut microbiome is changing the way we think about our bodies.

The brain, immune system, and gut appear to be interconnected — suggesting taking care of our gut health is key to both physical and mental health.

In his latest book, "The Immune Mind," Dr. Monty Lyman, a medical doctor specializing in psychiatry and a research fellow at the University of Oxford, argues that "we're part of a loop of mind, body, and microbe."

For instance, the gut microbiome helps to "train" our immune system to distinguish friend from foe to prevent chronic inflammation, Lyman told Business Insider. Chronic inflammation is linked to symptoms including fatigue, pain, and persistent infections, as well as longer-term health concerns including dementia, depression, and diabetes.

And in the early 2010s, scientists discovered that lymphatic vessels — the veins and arteries of the immune system — exist in the meninges — the protective membranes that surround the brain — proving the immune system and brain are linked, Lyman writes in the book.

"In the last 10 or so years, we've discovered new anatomy that links the immune system to the brain and discovered immune cells in the brain that we previously thought weren't in there," he told Business Insider.

He hopes this knowledge will provide a new, more holistic framework for the way we look at our health.

"There's no mental health condition that isn't also physical. And there's no physical health condition that doesn't have a mental aspect to it," Lyman said.

With this in mind, it may be tempting to reach for products that promise to boost our gut health: the US digestive health market is forecast to continue to grow over the next five years, making up to $7.2 billion by 2028, according to Mintel. But most experts, Lyman included, emphasize that there's no quick fix to health and that eating a healthy diet is the best way to achieve good gut health.

"Instead of thinking about it as trying to look for a silver bullet pill, the idea of caring for the community within you, realizing that you are a community, and every time you have a meal, even if there are no other humans around you, you are partaking in a communal meal," Lyman said.

Lyman shared three things he does to cultivate a healthy gut microbiome for his mind and body with BI.

Gut gardening

Lyman finds it helpful to think of his gut microbiome as a garden that needs tending to. He calls this "gut gardening," and makes sure he eats enough of the right foods to feed his microbial community.

"So providing them [the microbes] with the right fertilizer, which is the fiber, and also the right seeds, which is the fermented foods," he said.

Dietary fiber, which comes from plants including fruits and vegetables, legumes, nuts, and seeds, is prebiotic, meaning it feeds the microbes that live in the gut lining. There's strong evidence to suggest that a diverse microbial community is a healthier one, and eating a wide range of plants helps to create this biodiversity, Lyman said.

Meanwhile, fermented foods, such as kimchi, sauerkraut, and kombucha, are probiotics, meaning they contain live bacteria that can help populate the gut microbiome, he said.

Making his own sauerkraut

A 2021 study from Stanford University found that people who ate a diet high in fermented foods for 10 weeks had even more diverse microbiomes than those who ate a high-fiber diet. They also had reduced inflammation biomarkers.

"There was evidence that basically people didn't have enough bacteria to break down all of the fiber," Lyman said of the study. The daily recommended intake of fiber is 30 grams in the US, but most Americans eat around 15g a day, he said. So while eating more fiber is good, you should introduce it slowly and eat probiotic-rich foods at the same time.

After reading the findings, Lyman started experimenting with fermentation himself, and he eats fermented foods every day, he said. His favorite fermented food is sauerkraut made with cabbage, salt, and thyme.

Making more time for rest

Lyman has also started to be more intentional about what he commits to so he can ensure he has time to rest. "I've tried to be more proactive and ruthless in cutting out potential sources of stress, even if it's at the expense of various ambitions and plans," he said.

This is because chronic stress can cause chronic inflammation.