Trillions of bacteria inhabit the human gut. While some of the bacteria are unhealthy pathogens, a large number are beneficial to their hosts. Known as the gut microbiota, these bacteria influence digestion, mood and other aspects of human health.
Some of the lifestyle decisions we make can change the composition of the microbiota, for the better, and for the worse. The typical American diet is filled with processed foods and a sedentary lifestyle can negatively affect bacterial colony size and diversity within the body. Many people now take probiotics to help their microbiota overcome these effects. Now there is evidence that probiotics may provide special benefits to athletes.
Diversity in the microbiota could be beneficial to athletes for several reasons. A 2015 study on mice published in The Journal of Strength & Conditioning Research suggests that gut microbial status is crucial for exercise performance. In this study, Taiwanese scientists found that mice with greater intestinal flora diversity lasted longer in swim-to-exhaustion tests. The mice also produced more antioxidant enzymes, which protect the body from the stress of intense physical activity.
A 2014 study published in the European Journal of Applied Physiology found that taking a probiotic helped runners perform better on a treadmill in 95-degree heat. Bacteria can often leak from the gut into the bloodstream during strenuous activity, which can trigger inflammation that could raise core temperature. Higher core temperatures interfere with the body’s ability to tolerate hot conditions. Probiotics make the gut lining healthier to reduce leakage of pathogenic molecules or bacteria and control temperature-raising inflammation. The subjects of this study demonstrated this theory in that those who took probiotics were able to exercise longer than those who did not.
Microbes in the gut release hormones that may benefit the athlete both physically and mentally. Gut microbes can initiate the release of dopamine, for example, which is a brain chemical involved in movement, motivation, and reward. The microbiota may stimulate the release of serotonin, which helps to transmit impulses between nerve cells and regulate body processes, and GABA, norepinephrine, acetylcholine and melatonin that regulate mood.
Intestinal microbiota interacts with the host’s immune system to help the host’s body tell the difference between friendly and harmful bacteria. This property could help keep athletes from getting sick during heavy training.
Scientists already know that gut bacteria can vary widely between individuals, but they are just beginning to understand why some people have healthier numbers of beneficial gut bacteria than others.
Shifts in the microbiota composition are often correlated with certain conditions, including allergies, asthma, obesity and obesity-related disorders. Now there is evidence that physical activity itself not only benefits from the microbiota but exercise actually increases the diversity and number of gut bacteria.
A 2014 study published in Gut investigates this effect. In this study, researchers compared the gut microbes of 40 professional rugby players with those from non-athletes. They found the rugby players had twice the microbial diversity on average.
Another study on diabetic mice suggests exercise has a direct effect on the variety of microbes inside the gut. Researchers at University of Calgary compared intestinal microbes collected from physically active mice and sedentary mice for six weeks. They found greater numbers of select Firmicutes species and Bifidobacterium in the active mice. The scientists said more research is necessary to determine exactly how exercise influences gut microbiota.
People who exercise report catching fewer colds, according to studies cited by the American College of Sports Medicine (ACSM), but at the same time, too much exertion has been shown to have the opposite effect and may increase the risk for upper respiratory infections (URIs). One of the studies followed 2,311 marathon runners who ran the Los Angeles Marathon and found that one out of seven runners got sick in the week following the marathon, a rate five times higher than for people who trained for the race but did not run. Researchers in South Africa confirmed the results in a different trial of marathon-type exertion.
The ACSM researchers concluded that a steep drop occurs in the immune systems of marathon runners, and this lag in immune function gives viruses and other pathogens an opportunity to gain a foothold. Taking probiotics could lessen this steep drop in immune function and reduce the development of upper respiratory infections and other infectious diseases among extreme athletes.
Researchers continue to study the different ways probiotics may help athletes. These studies will likely yield information that leads to greater understanding of how probiotics support the immune system, control core temperature, extend endurance and more.