Imagine the hustle and bustle of a large city, people streaming along the sidewalks and crosswalks to get where they’re going. This mirrors the patterns of the microbiome within an athlete’s body at a microscopic level. Trillions of microorganisms consisting of thousands of different species, including bacteria, fungi, viruses, and parasites, happily coexist in a healthy gut and throughout the body in all stages of life.
The importance of these microscopic organisms has undergone increased scrutiny as athletes try to stay healthy to continue the demanding routines of training and racing. As we gain knowledge of the impact of these microbes on the human body, research has begun to focus on how various training methods and dietary choices affect physiological functions and, ultimately, athletic performance.
Addressing your gut microbiome is not a one-and-done situation. This unique combination of microorganisms is defined at birth by our DNA and influenced by everything from our environment and food choices. Certain microbes benefit both the human body and the microbiota itself (symbiotic), while others have the potential to promote disease (pathogenic). The delicate balance of symbiotic to pathogenic flora is critical for proper physiological function within the body.
High-carb or high-protein? What to feed your microbiome for athletic performance
Many endurance athletes utilize a nutrition strategy that adjusts the proportion of carbohydrates and protein consumed as training changes throughout the year. This method of strategic use of exercise training and nutrition, or nutrition only—with the goal of physiological adaptations to support exercise performance is termed “dietary periodization.” But how do changes to what you eat affect your gut microbiome?
Furber et al. (2022) examined the differences in microbial flora and performance among endurance athletes who undertook a short-term high-carbohydrate or a high-protein diet. The study assessed the impact of short-term (7 days) high-protein (40% protein, 30% carbohydrate, and 30% fat macronutrient distribution) versus an energy-matched high-carbohydrate diet (10% protein, 60% carbohydrate, and 30% fat macronutrient distribution) on gut bacterial, viral and fungal communities using a double-blind, randomized control trial design within a cohort of well-matched, highly trained endurance runners (n =16).
From these 16 participants, eight participants were assigned a high-protein diet intervention and eight a high-carbohydrate intervention. Through the examination of stool samples, athletes were assessed for pre-dietary, mid-, and post-dietary change in gut microbiota. Additionally, each participant performed a time trial to exhaustion at three time points: pre-intervention, mid-intervention, and post-intervention, to assess the relative impact of the dietary change and the resulting microbiome on performance.
Results suggested that athletes following the high-protein regime experienced a less stable gut microbiome. All participants in the high-protein group saw a decreased performance at some level: on average, the high-protein group experienced a performance reduction of 23.3% in the mid-intervention time trial to exhaustion. But once the high-protein group returned to their pre-intervention dietary pattern, their performance in the time trial was comparable to pre-intervention data.
In contrast, those participants following a high-carbohydrate diet improved mid-intervention time trial performance by 6.5%, and seven of the eight improved their performance relative to the pre-intervention values.
The analysis of types of gut phagosome revealed significantly reduced diversity and altered composition within the high-protein diet. In essence, the results suggest the high-carbohydrate diet supports a more stable gut microbiome associated with better performance during time trials in a group of endurance athletes.
The authors acknowledge several limitations, including small sample size, lack of a mechanism for linking changes in microbial communities more definitively to performance, and the inability to guarantee participant compliance with the dietary intervention. Regardless, the authors contend that the diets in this study were well-controlled and carefully balanced, which makes it unlikely that the protein content alone caused the decrease in performance.
Happy gut, happy racing
Though dietary advice is not one-size-fits all, there is a large and loud consensus in the research that carbs are the endurance athlete’s best friend. Adequate carbohydrate consumption is more than eating to fuel your workouts: carbs can reduce GI distress in runners, keep hormone levels in check, and keep your microbiome happy, which may help you hit that PR in your next race.
We know that consuming a variety of probiotics, a variety of grains, fruits, vegetables, and fermented foods is associated with greater gut stability, which may have positive health and performance benefits. Future research should focus on how changes in gut flora may impact nutrient absorption or intestinal permeability, which ultimately could change the communication between the gut and the brain. This connection and its associated implications for the athlete’s perceived effort and performance could provide vital information for elite and recreational athletes.
Kim Schwabenbauer, PhD, RD, CSSD, LDN, is a former professional triathlete turned registered dietitian, professor, consultant, speaker and triathlon coach with an emphasis in overall health, wellness and sports nutrition.