An innovative study finds a link between our heart health and the health of our gut, highlighting the importance of physical exercise for keeping both at optimal levels.

If the latest medical research has taught us anything, it's that our gut bacteria hold the key to our health.

The trillions of micro-organisms that live in our gut seem to control every aspect of our well-being, from the size of our belly to the risk of chronic disease and even that of mental health conditions.

So, it's essential that we maintain a healthy gut. The bacteria we host inside us can keep us healthy and happy, but we must return the favor.

Keeping a diverse range of microbes ensures that we have more of the "friendly" bacteria that benefit our body. Having a healthful and varied diet is perhaps the most obvious way to do so, but new research adds a vital ingredient: a good workout.

Keeping our heart healthy and fit through physical exercise may also increase the number of beneficial gut bacteria, suggests the new study.

Ryan Durk, of the Department of Kinesiology at the San Francisco State University in California, is the first author of the new paper, which was published in the International Journal of Sport Nutrition and Exercise Metabolism.

Studying gut and heart health

Durk and colleagues examined the cardiovascular fitness of 20 men and 17 women, using a treadmill test.

The researchers also determined the participants' body fat composition by asking them to step inside a so-called BOD POD—a chamber that can measure a person's fat mass and their lean mass, using air displacement plethysmography.

Participants were also asked to keep a food diary for 7 days and to provide the researchers with stool samples at the end of the study period.

Durk and team examined the bacterial composition of the stool samples, focusing on the ratio of a class of bacteria called Firmicutes to another class of bacteria called Bacteroides.

The Firmicutes-to-Bacteroides ratio is a standard measure of gut health, with studies linking an imbalance in this ratio to conditions such as obesity or irritable bowel syndrome (IBS).

Exercise is key for healthy gut bacteria

The study revealed that people with the highest cardiovascular fitness also had a higher ratio of Firmicutes to Bacteroides.

As the researchers explain, a higher number of Firmicutes has been linked with metabolites that stop harmful bacteria in the gut from migrating to the rest of the body.

"These metabolic byproducts help strengthen the intestinal lining and help prevent leaky gut syndrome," says Durk, adding that the findings further support the idea of "exercise as medicine."

"When we say that phrase, we think of it as meaning that exercise will help people stay healthier and live longer. But you don't think about your gut bacteria," says the first author.

"We now know that exercise is crucial for increasing beneficial bacteria in the gut."

–Ryan Durk

In the future, the researchers hope that similar studies will replicate their findings, ultimately leading to personalized exercise programs that could be prescribed to improve gut health.

"We're not there yet," says Durk, "but this [study] helps create that foundation."