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According to a study in the journal mSystems, consuming too much protein could come with added risks.Related video above: Probiotics: Do they work and are they safe?In the study, researchers assessed the stability of gut microbes in trained endurance athletes, and how microbial composition may change with protein and carbohydrate consumption.Albeit small (the study looked at just 16 runners), the results were informative. Researchers analyzed the participants�� athletic performance and gut bacteria diversity (via stool samples) for seven days while on a high-protein diet, which was made up of 40% protein, 30% carbs, and 30% fat. This was compared to a group on high-carb diet of 10% protein, 60% carbohydrate, and 30% fat.Researchers found that when protein was the biggest component, it resulted in a disturbance in the stability of the gut microbiome—with less bacterial diversity—and a notable reduction of about 23% in running performance, as measured by a time trial to exhaustion. With the high-carb diet, however, there was an improvement in performance of about 6%, as well as more stability in the gut microbiome. These results suggest that there’s a strong connection between your gut bacteria and athletic performance, study co-author Justin Roberts, Ph.D., associate professor in health and exercise nutrition at Anglia Ruskin University in the U.K. told Runner’s World. “We can’t be certain that the high amount of protein in the body was entirely responsible for the significant drop in performance,�� he said. “But it was found that there were certainly changes to the microbiome following a short-term, high-protein diet, which appeared to be associated with performance.�� All About the Influence Your Food Choices Have on the GutOne drawback to the recent study is its very small participant size, but previous, larger-scale research has also indicated that high amounts of protein could be a gut changer, according to Amanda Kostro Miller, R.D., registered dietitian and medical reviewer at Botanical Institute. For example, a research review published in Frontiers in Physiology in 2017 points out that different protein sources affect gut microbiota. Another meta-analysis published in February 2022 says protein can negatively and positively affect the microbiome, depending on sources, content, and diet as a whole, among other factors. (Keep in mind the 29 studies involved in the meta-analysis were not conducted on humans but rather on animals and in vitro.)The negative affects of high amounts of protein are particularly potent when accompanied by low carbohydrate consumption, Miller told Runner’s World.“High-protein, low-carb diets can have a detrimental effect on gut health by negatively changing the microbiota of the gut,�� she said. “Following that kind of diet can reduce the production of short-chain fatty acids (SCFAs) within the gut.�� Research published in Frontiers in Microbiology notes that SCFAs produced by gut microbiota are recognized as potential regulators of skeletal muscle metabolism.That’s a big deal, and not just for athletic performance, she added. Produced when you eat foods rich in fiber and resistant starch—such as bananas, cooked and cooled rice, beans, avocados, apples, and oats—SCFAs may influence the gut-brain connection, and also play an important role in maintaining the integrity of the intestinal barrier of the gut. These SCFAs may also reduce inflammation, regulate the immune response, and can lower risk of developing some cancers, particularly colon cancer. In fact, one particular type of SCFA called butyrate has been shown in studies to potentially inhibit tumor growth in a variety of colon cancer cell types. Butyrate may also help with inflammatory conditions, like inflammatory bowel disease, as other research suggests.“Because of this, following a diet with adequate carb intake is essential for optimal health within the gut, and for your overall health and athletic performance,�� said Miller.The bottom line here: While there is more research needed on the effects of gut bacteria on your health and athletic performance, studies do point to the importance of carbohydrates in creating a healthy microbiome which can play out in your well-being in various ways.