Asian J Sports Med. 2019 March; 10(1):e82404. Published online 2019 February 24. doi: 10.5812/asjsm.82404. Research Article Impact of Ketone Salt Containing Supplement on Cardiorespiratory and Oxidative Stress Response in Firefighters Exercising in Personal Protective Equipment Matthew John McAllister 1, * , Angelia Maleah Holland 2 , Harish Chander 3 , Hunter Scott Waldman 3 , JohnEric William Smith 3 and Steven Allen Basham 3 1 Metabolic and Applied Physiology Lab, Department of Health and Human Performance, Texas State University, San Marcos, United States 2 Nutrition, Exercise and Stress Lab, Department of Kinesiology, Augusta University, Augusta, United States 3 Department of Kinesiology, Mississippi State University, Starkville, United States * Corresponding author: Metabolic and Applied Physiology Lab, Department of Health and Human Performance, Texas State University, San Marcos, United States. Email: mjm445@txstate.edu Received 2018 July 19; Revised 2018 November 02; Accepted 2018 December 28. Abstract Background: Firefighters have the highest risk of on duty death due to cardiovascular disease which may be caused by excessive oxidative stress (OS). Animal studies have shown that ketone bodies may reduce OS; however, human trials are needed. Objectives: To examine the effects of a supplement containing ketone salts (KS) on blood OS and cardiorespiratory responses in firefighters exercising in personal protective equipment. Methods: Nine firefighters supplemented with KS or a calorie- and flavor-matched placebo (PLA) twice per day for 7 days in a random- ized, crossover design. On the eighth day, firefighters arrived for testing after ≥ 8 hour fast and ingested the assigned supplement 35 minutes before performing the exercise task (35 minutes at 60% VO2peak intensity) wearing personal protective equipment (i.e., turnout gear, self-contained breathing apparatus, air tank, gloves). Blood was sampled pre- and post-exercise (post periods: imme- diately, 30 minutes and 24 hours) and analyzed for markers of OS including red blood cell (RBC) levels of glutathione (GSH), oxidized glutathione, superoxide dismutase (SOD), as well as plasma levels of SOD, catalase, total antioxidant capacity, malondialdehyde, and glucose. Results: There was no treatment effect or treatment × time interaction (P > 0.05) for any of the markers of OS. However, the exercise protocol resulted in significant increases in RBC levels of SOD from pre- to immediately post-exercise and decreased RBC levels of GSH from pre- to 30 minutes post-exercise. Ingestion of KS resulted in a significant increase in ketone levels and reduction in heart rate during the exercise test. Conclusions: These findings suggest that 7 days of supplementation with a KS supplement does not impact markers of OS but reduces heart rate. Keywords: Beta-Hydroxybutyrate, Ketosis, Substrate Oxidation, Central Nervous System, Heart Rate, Ergogenic Aid 1. Background Firefighters (FF) have the largest occupational-related risk of death due to cardiovascular disease (CVD) which may be caused by excessive oxidative stress (OS) (1). Fire- fighter occupational activities have been shown to pro- duce increases in markers of OS due to increased metabolic demand from a variety of stressors (2-4). While acute expo- sure to moderate amounts of OS and inflammation is ben- eficial for stimulating favorable adaptations (5), chronic OS exposure may be a major contributor to increased CVD prevalence in FF (6). OS is associated with reactive oxygen species (ROS) pro- duction that overwhelms endogenous antioxidants. Di- etary interventions such as caloric-restriction (7) exoge- nous antioxidants (8), and a low-carbohydrate, ketogenic diet (9), have demonstrated improvements in endogenous antioxidant capacity and decreased OS. In addition, a keto- genic diet is associated with improved mitochondrial func- tion via increased levels of uncoupling proteins (9), which results in less ROS production reducing OS (10-12). Exogenous ketones may facilitate ketosis without fol- lowing a ketogenic diet which involves extreme restric- tions on carbohydrate intake (13, 14). It is not clear whether or not ketone bodies themselves are responsible for im- Copyright © 2019, Author(s). This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International License (http://creativecommons.org/licenses/by-nc/4.0/) which permits copy and redistribute the material just in noncommercial usages, provided the original work is properly cited.