By Jennifer Kurtz, PhD(c), CISSN, CSCS, EP-C

Photo: Justin Luau

Jennifer Kurtz is an exercise physiologist with expertise in nutrition, energetics and metabolism, and sport and exercise. Her research covers all aspects of cycling performance, ranging from power output to oxygen consumption, heart rate, perceived exertion, NO metabolite production, GI distress, and more. Kurtz favors interdisciplinary approaches to human health-related questions, incorporating physiological approaches and nutritional methods to understand the whole-human response to exercise and nutrition, with a focus on elevating awareness of research on female athletes. In addition to all that, she still has time to compete as a CAT 1 mountain bike racer.


Consuming supplements for endurance performance has become much more widespread in the past decade. Dietary supplements are not intended to replace a healthy balanced diet, but they can play a meaningful role in helping athletes consume the proper amounts of macronutrients, micronutrients, and calories; however, the overall need and efficacy of certain ingredients remain controversial.

Numerous supplements have been investigated to help improve or optimize endurance performance and recovery, support adaptations, or exhibit health benefits. Before using those supplements, athletes should be aware of the latest research recommendations, and efficacy of certain supplements. There are thousands of ingredients and supplements on the market, but below I will highlight some common ones. 


Caffeine is a naturally derived stimulant found in nutritional supplements and can also be found in coffee, tea, energy drinks and gels, chocolate, etc. There is consistent and strong scientific evidence to show that caffeine operates as an ergogenic aid in several endurance situations.

Studies show that – when 3-9 mg/kg of caffeine are ingested 30-90 minutes before exercise – caffeine can improve endurance exercise capacity (Kerksick et al., 2017). It’s also been shown to be the most effective ergogenic aid for aerobic exercise due to its ability to increase energy expenditure, time-trial performance in cyclists, spare muscle glycogen, repeated-sprint performance, lower ratings of perceived exertion, and decreased perception of muscle pain (Kerksick et al., 2017).

The findings on caffeine for its ability to impact strength and muscular performance are equivocal, though, and more research is needed to better determine how caffeine affects strength performance for endurance athletes.

Editor’s note: For more on caffeine, see Caffeine as a Nootropic.

Medium-chain triglycerides (MCTs)

MCTs can enter directly into the mitochondria and can be used for energy via the beta-oxidation, the process where fats are broken down to yield energy (Vitale & Getzin, 2019). In theory, this provides the athlete with a readily available fat source for energy, thereby sparing glycogen (Kerksick et al., 2017). Given that theory, it’s little surprise that there has been a recent focus on medium-chain triglycerides (MCTs) to enhance endurance performance. 

Some studies suggest improved cycling performance with MCTs, and other studies actually show ergogenic effects when taking MCTs versus CHOs; however – and this is a big “however” – most studies also report MCTs can cause GI distress (Kerksick et al., 2017). Given the currently available evidence, the International Society of Sports Nutrition (ISSN) currently considers MCTs in the category of “little to no evidence to support efficacy and/or safety.”


Nitrates are often found in beets, beetroot juice, and dark green leafy vegetables. Once consumed, nitrates are converted to nitrite by oral bacteria and then to nitric oxide in the gut. Nitrates have gained significant attention in the endurance athlete population for the proposed benefits of improving oxygen consumption, and there is promising evidence to show that dietary nitrates can improve exercise performance (Gao et al., 2021).

Research shows that nitric oxide has beneficial effects on the human body, especially for endurance athletes, by improving vasodilation, blood flow, oxygen utilization, mitochondrial respiration and biogenesis, glucose uptake, muscle contraction/ relaxation, and blood pressure (Vitale & Getzin, 2019).

Dietary nitrates can improve muscle economy and efficiency, mitigate fatigue, improve cardiorespiratory performance, decrease effort at submaximal loads, and reduce oxygen cost during exercise (i.e., cycling). Lowering oxygen cost helps improve mitochondrial efficiency, ATP synthesis, exercise tolerance, and performance.

Editor’s note: For more on how PreRace 2.0 achieves many of the effects of nitrates using a non-nitrate source, see Nitrosigine® Circulation Booster.


Probiotics are considered “live food ingredients,” and are often found in kombucha, yogurt, kimchee, sauerkraut, miso, and other fermented foods. They can also be taken in a supplement form.

Probiotics are shown to improve health, gut microbiota, and immune function while assisting with lactose intolerance, antimicrobial activity – in short, reducing GI distress by improving gut function (Verna & Lucak, 2010).

Recently, there has also been focus on a crosstalk between the gut microbiota and mitochondrial function through metabolites such as short-chain fatty acids (SCFAs) (Verna & Lucak, 2010; Clark & Mach, 2017). The interaction between microbiota and mitochondria appears to occur primarily through hormone, immune, and humoral signaling in a back-and-forth involving SCFAs. SCFAs are produced by the gut, and there’s evidence suggesting they might influence mitochondrial functions related to energy production, mitochondrial biogenesis, redox balance, and inflammatory cascade, making probiotics a potential aid for endurance performance (Clark & Mach, 2017).

Only a few studies exist to show the beneficial effects of probiotics on endurance performance, so more research is needed to better define the ergogenic effects. However, research does suggest that probiotics may benefit endurance athletes susceptible to URI or GI symptoms, athletes who travel frequently, or athletes who are susceptible to infection.


The Sports Nutrition field is constantly evolving, so it is essential to stay up to date with the latest nutritional strategies for endurance athletes. This blog highlighted and summarized the latest evidence-based research and strategies to equip endurance athletes and coaches with current knowledge related to dietary supplements.

Of the supplements considered here, caffeine has the largest body of evidence to support its ergogenic effects for endurance performance and nitrates have moderate supporting evidence. There is a paucity of quality research on probiotics and MCTs. Though there is some evidence suggesting beneficial effects for endurance performance, more research would help confirm those benefits.

Note with any new supplement, FDA is not required to review the ingredients for safety and effectiveness before they are marketed, so there is a risk when consuming supplements. It is recommended that endurance athletes should consume whole-food and nutritionally dense food sources to acquire their nutritional needs; however, we understand that athletes consume supplements, but they are encouraged to consume supplements from trusted and FDA-approved sources.

Editor’s note: For more on First Endurance’s approach to purity and quality, see our Statement on Manufacturing Standards.


Clark, A., & Mach, N. (2017). The crosstalk between the gut microbiota and mitochondria during exercise. Frontiers in physiology, 319.

Kerksick, C. M., Arent, S., Schoenfeld, B. J., Stout, J. R., Campbell, B., Wilborn, C. D., . . . Kreider, R. B. (2017). International Society of Sports Nutrition position stand: nutrient timing. Journal of the international society of sports nutrition, 14(1), 1-21.

Verna, E. C., & Lucak, S. (2010). Use of probiotics in gastrointestinal disorders: what to recommend? Therapeutic advances in gastroenterology, 3(5), 307-319. 

Vitale, K., & Getzin, A. (2019). Nutrition and supplement update for the endurance athlete: Review and recommendations. Nutrients, 11(6), 1289.

August 10, 2023 — First Endurance
Tags: research

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