Is aerobic exercise like running, cycling — or rugby — the new yogurt?
We'll explain the rugby reference, but let's first scan the microbe-gut-health situation.
Probiotics are wildly popular — for good reason, given the fast-growing evidence of their broad health benefits.
The term probiotic means "for life,” and refers to any living microorganism which, when consumed in adequate amounts, confers a health benefit.
And the term “prebiotic” refers to fiber-like chains of sugars such as FOS and inulin, which fuel the growth of one or more probiotic bacteria strains.
Most of the benefits associated with probiotic bacteria stems from their effects on your gut microbiota — the totality of bacteria and other microbes living in or on your body. (“Microbiome” refers to the genes in those microbes.)
These trillions of “friendly” microbes help break down your food and produce certain nutrients in the process.
The beneficial Lactobacilli and Bifidobacterium cultures commonly used to ferment milk into yogurt — and to naturally “pickle” vegetables — are prime examples of probiotic microbes.
Until now, it’s been believed that the only way to positively affect the microbiome in your gut is through probiotics, such as yogurt, or prebiotics, such as inulin and FOS.
Probiotics exert their beneficial effects by tipping the balance of bacteria in your gut toward the friendly kinds.
Growing the proportion of friendly bacteria in your gut keeps “unfriendly” bacteria in check. When unfriendly bacteria gain the upper hand in your gut, that imbalance can lead to a host of problems.
Aside from gut conditions like irritable bowel syndrome (IBS), ulcerative colitis, and Crohn’s disease, disorders links to the composition of your gut microbiota include asthma, cancer, candida, celiac disease, diabetes, eczema, heart disease, malnutrition, multiple sclerosis, and obesity.
And there’s growing evidence that the composition of your gut microbiota can improve or degrade your cognitive abilities and mood — see Live Cultures May Lift Mood and Cultured Foods for Social Comfort.
In part, this list of disorders related to the composition of your gut microbiota stems from the influence of gut microbes on inflammation and other aspects of the immune system.
Now, exciting evidence from two new studies suggests that fermented foods and probiotic supplements aren’t the only ways to tip the balance of your gut bacteria in a healthy direction.
So, if yogurt isn’t your thing — or you’re not sure which probiotic pills or powders pack the healthiest punch — these studies constitute great news.
Exercise benefits the bacterial balance in your gut
The two new companion studies — one in mice and one in people — come from researchers at the University of Illinois at Urbana-Champaign (Allen JM et al. 2017).
And the results deliver the first definitive evidence that exercise can tip the balance of gut bacteria in a healthy direction.
For their animal study, the Illinois researchers transplanted bacteria-rich fecal material from two groups of mice — those who had exercise and those who had not — into sedentary mice lacking gut microbes.
Changes in the microbiota of the recipient mice was identical to the mice from whom they’d received the microbiota.
In other words, the microbiota created by the transplant mirrored the microbiota profile of the mice from whom they received the transplants.
Next, the Illinois team exposed the mice to a substance that leads to inflammation in the colon — and the animals implanted with fecal material from the active mice were much better at resisting inflammation and healing, compared with mice that received a fecal transplant from couch-potato mice.
For the human study, the Illinois team recruited 32 adults, some at a healthy weight, and some obese.
The scientists took samples of the participants’ gut microbiota, then placed them all on a regimen of 30-60 minutes of aerobic/cardio exercise, three times a week for six weeks.
The researchers then re-sampled participants’ gut microbiomes at the end of the exercise time, and again after an additional six weeks of no exercise.
SCFAs (short-chain fatty acids) are produced by friendly gut bacteria in the gut, so SCFA levels were measured in fecal samples provided by the participants at the end of each six-week phase of the study.
The team found higher levels of SCFAs in both types of participants — healthy weight and obese — after six weeks of exercise.
Confirming that exercise had boosted levels of beneficial bacteria, the levels of SCFAs declined after the following six weeks of returning to a sedentary routine.
According to study leader Jeffrey Woods, “These are the first studies to show that exercise can affect your gut, independent of diet or other factors.”
Review linked exercise to gut health; Rugby players scored probiotic goals
The Illinois studies reinforce the findings of a recent evidence review — and echo the first-ever clinical study.
Recent exercise-gut evidence review
Last year, Italian researchers published a review that covered more than 80 studies, and concluded that exercise enriches the diversity of your microbiota, and raises the proportion of beneficial bacteria.
As they wrote, “… exercise can be used as a treatment to maintain the balance of the microflora or to rebalance ... dysbiosis [microbial imbalance], thus obtaining an improvement of the health status.” (Monda V et al. 2017)
Clinical study tested rugby players
An Irish clinical study published four years ago was the first-ever to find that exercise enhances people’s gut microbial diversity.
University researchers recruited 40 professional rugby players to assess the effects of exercise on gut bacteria (Clarke SF et al. 2014).
The scientists studied fecal and blood samples from the players, who routinely engaged in rigorous training, but nonetheless varied in terms of body mass index.
And each player completed a diet survey designed to determine the typical eating patterns.
This test group was compared to a control group of 46 healthy men who weren’t athletes, but matched the physical size and age of the rugby players.
All the participants completed food questionnaires and recorded their levels of activity.
And, even though the athletes had much higher levels of creatine kinase enzymes — which indicate muscular damage stemming from exercise — they had lower levels of inflammation.
They also had a broader range of gut microbiota than the control group, and higher levels of certain healthy bacteria, including a species (A. muciniphilla) linked to lower rates of obesity and diabetes.
Interestingly, the results also showed that the players who reported eating the most protein had the broadest, most desirable degree of microbial diversity.
That link which doesn’t prove a cause-effect connection, but with Paleo and other high-protein diets being so popular, it’s a correlation worth further probing.