The Zero Calorie Ultra

Jun 19

Would you run 100 miles without eating? Some athletes have tried — but should you?

In this episode of Your Diet Sucks, we explore the history and science of fasting for endurance athletes. From early experiments in “train low” strategies to the modern hype around intermittent fasting, we dig into why runners and athletes are drawn to the idea of doing more with less fuel. We break down the potential benefits of fasting — fat adaptation, metabolic flexibility, and simplicity — alongside the risks and downsides, like reduced performance, higher injury risk, and impaired recovery.

If you’ve ever wondered whether fasting can actually help your running or if it’s just another diet trend, this episode gives you the evidence-based answers.

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Fensham NC, Heikura IA, McKay AKA, Tee N, Ackerman KE, Burke LM. Short-Term Carbohydrate Restriction Impairs Bone Formation at Rest and During Prolonged Exercise to a Greater Degree than Low Energy Availability. J Bone Miner Res. 2022 Oct;37(10):1915-1925. doi: 10.1002/jbmr.4658. Epub 2022 Aug 10.

Vilaça-Alves J, Muller F, Rosa C, Payan-Carreira R, Lund R, Matos F, Garrido N, Saavedra FJ, Machado Reis V. Cardiorespiratory, enzymatic and hormonal responses during and after walking while fasting. PLoS One. 2018 Mar 1;13(3):e0193702. doi: 10.1371/journal.pone.0193702. PMID: 29494664; PMCID: PMC5833199.

Roche, D. (2021, June 11). Fasted training may have long-term risks, especially for female athletes. Trail Runner Magazine. https://www.trailrunnermag.com/training/trail-tips-training/fasted-training-may-have-long-term-risks-especially-for-female-athletes/

Oakes, John. The Fast: The History, Science, Philosophy, and Promise of Doing Without. United States, Avid Reader Press / Simon & Schuster, 2024.

The works of Benjamin Franklin, Vol. xi letters and MISC. writings 1784-1788: Online library of liberty. The Works of Benjamin Franklin, Vol. XI Letters and Misc. Writings 1784-1788 | Online Library of Liberty. (n.d.).

Sandip T Gaikwad, "Apprehending Concept, Canons and Types of Fasting in Buddhism", International Journal of Innovative Research and Creative Technology vol. 2, issue 4, pp. 164–168. 2017.

Zoë Rom

Zoë Rom is a science and environmental journalist with bylines in The New York Times, Outside, and High Country News. She co-hosts Your Diet Sucks, an evidence-based nutrition and wellness podcast, with registered dietitian Kylee Van Horn, RDN, where they investigate how wellness culture distorts science and how athletes can do better. A Colorado-based ultrarunner, she finished second at the Leadville Trail 100 and top five at Run Rabbit Run 100. Her reporting and commentary focus on the intersection of sport, science, and the wellness industry's long history of selling women their own anxieties.