Research paper
Burke LM, Ross ML, Garvican-Lewis LA, Welvaert M, Heikura IA, Forbes SG, Mirtschin JG, Cato LE, Strobel N, Sharma AP, Hawley JA. Low carbohydrate, high fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers. Journal of Physiology. 2017 May 1;595(9):2785-2807. doi:10.1113/JP273230. PMID: 28012184; PMCID: PMC5407976.
Why we cite it
Randomised controlled trial in 21 elite male race walkers (world-class, including Olympic representatives) comparing three dietary strategies — high carbohydrate (HCHO), periodised carbohydrate (PCHO), and low-carbohydrate high-fat/ketogenic (LCHF) — during 3.5 weeks of intensified training. The study is an unusually well-controlled test of ketogenic diets in elite athletes, and the reasons are worth stating rather than summarising: it used world-class athletes, controlled energy intake, measured both metabolic and performance outcomes, and included a race-simulation test. Key finding: LCHF successfully produced dramatic fat oxidation (peak 1.57 g/min, among the highest ever reported), confirming metabolic adaptation is real. However, fat oxidation requires ~8% more oxygen per calorie than carbohydrate oxidation — an inherent biochemical limitation that impaired exercise economy at race-relevant speeds and negated the performance benefits of training (HCHO -6.6%, PCHO -5.3%, LCHF +1.6%). Provides the critical counterbalance to cfa08 (Volek & Phinney 2012): fat adaptation is real, but doesn’t automatically translate to performance.