Attention, couch potatoes. As if it weren’t enough that exercise has a positive impact on your mood, weight and ability to ward off numerous chronic diseases, now it’s been linked to gut health — in a good way. The study, published in Experimental Physiology, is the first to look at a link between gut microbiota diversity and cardiorespiratory fitness. While gut bacteria doesn’t immediately come to mind as a healthy phenomenon, a growing body of research indicates that having different species of bacteria in the gut with populations that approach even distribution can be related to good health.

This newest research draws a closer correlation, suggesting that humans with higher cardiorespiratory fitness levels are more likely to have this desirable level of gut microbiota diversity. Further, the study revealed the oxygen-to-tissue transport efficiency is a far better indicator of good gut bacteria diversity than either body fat levels or how much general physical activity a person gets.

The importance of bacteria in your belly

It can be a queasy thought, but the microbes in our body or on our skin have been proven again and again to affect human health in epic proportions. This is particularly true of the bacteria in your digestive tract, which is the fundamental indicator of GI health. No one wants to dwell on it, but the gut acts almost like a second brain, and its balance of beneficial and harmful bacteria keeps the body in peak health.

The term for a disturbance in this balance is “dysbiosis,” which is generally caused by unhealthy levels of bad “bugs” like bacteria, yeast or even internal parasites. When the gut’s balance gets out of whack, the GI tract’s mucosal layer can be damaged. This leads food proteins to head directly to the bloodstream. It sounds bad, and it is: Food proteins in the blood cause everything from inflammation to food sensitivities, all due to the body activating its immune system in response. The Central Nervous System soon gets in on the act if the digestive tract is irritated, and conditions from mood swings to diminished cognitive functions can be the result.

Not all scientists agree that enough research has been conducted to make wide claims about the relationship of gut bacteria and certain health issues. Lots of gut bacteria research still needs to be done before we can fully understand its role in health. Long-established mainstream medical experts like the Mayo Clinic recognize that gut bacteria differ between obese and lean people, for example. But it doesn’t draw hard-and-fast conclusions from this finding. Mayo notes that research has not established whether the variance in gut bacteria contributes to obesity or could result from obesity, instead. It further advised that taking probiotics probably won’t harm anyone, but the subject has not been researched fully enough to determine clear answers on a gut bacteria-obesity connection.

The exercise-good health link

The medical community has increasingly embraced the benefits of exercise to promote good health in recent decades. The most obvious is its role in controlling excess weight by burning calories, but being active also boosts HDL “good” cholesterol while diminishing triglycerides, which wreak havoc with heart health. Other health benefits of regular exercise including prevention of depression, different types of cancer, arthritis and of course type 2 diabetes.

This most recent research linking exercise and good health explored the effects of optimal activity levels on gut bacteria. This is a one-two punch. The first part of the improvement in health involves exercise at intensities high enough to encourage the heart to increase the volume of blood it pumps with each beat. Peripheral adaptations, aka an increase in the number of capillaries bringing oxygen from the blood to the muscles, also play a role. Both factors contributed to intensified cardiorespiratory fitness that in turn supports health by altering the presence and activity of gut microbes, along with the way they cluster.

How the gut bacteria-exercise study worked

Even before the study, scientists had correlated higher cardiorespiratory fitness and greater gut microbiota diversity. But they were undecided on whether the benefit was linked to better body fat percentages or simply the physical activities involved in daily living. This study examined 37 non-metastatic breast cancer survivors, a group chosen because the research community has already established that cancer treatment can trigger negative changes in cardio-metabolic health, from higher body fat percentage to decreased cardiorespiratory fitness to a predictable lowering of physical activity levels. Each of the women had finished treatment at least a year earlier.

To estimate their peak cardiorespiratory fitness, the participants each took a graded test that gauged how much energy they expended and estimate their highest level of cardiorespiratory fitness. Researchers also examined their gut microbiota levels using fecal wipes. The results did not support either body fat percentage or physical activity levels as primary indicators of gut bacteria diversity.

Instead, the subjects with the best cardiorespiratory fitness were clearly indicated as the ones with significantly higher gut microbiota diversity. Participants who weren’t as fit simply did not have the same levels of the type of gut bacteria diversity linked to better health. More analysis underscored the value of cardiorespiratory fitness. Researchers determined it made up almost a quarter of the gut bacteria diversity variance, even when body fat percentage was not factored.

Next steps

The team plans to expand on this finding, in part by studying how the gut microbiota diversity reacts to varying levels of exercise intensity. The end game would include assessing ways prescribed exercise could help clinical groups with their health.