Comment on: Substrate Metabolism During Ironman Triathlon: Different Horses on the Same Courses
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LETTER TO THE EDITOR
Comment on: Substrate Metabolism During Ironman Triathlon: Different Horses on the Same Courses Christopher C. Webster1 · James A. Smith1
© Springer Nature Switzerland AG 2018
Dear Editor, We refer to Maunder et al. [1], in which the metabolic effects of performance-level-specific dietary recommendations for Ironman triathlon athletes were modelled. Fat adaptation via a low-carbohydrate, high-fat (LCHF) diet was included in the model. The authors concluded that LCHF diets may be “appropriate for some lower performance amateurs” and that at low-amateur level, “dietary fat adaptation might be sufficient to support energy expenditure.” It may not have been meant this way, but the authors strongly imply that LCHF diets are only appropriate for low-amateur athletes and slow Ironman triathlon times. However, we feel the model and conclusions in Maunder et al. [1] present the reader with a level of certainty about the performance limits of fat adaptation that is not supported by the most recent LCHF research. The authors also mentioned the polarized debate surrounding the science of fat adaptation and exercise performance; we feel that all sides of this debate would benefit from an acknowledgement of the possibilities and uncertainties that exist surrounding fat adaptation. In their model, Maunder et al. [1] used 1.1 g min−1 as the upper estimate for mean rates of fat oxidation in their top-amateur category. Recent research from the labs of the LCHF advocates [2] and high-carbohydrate advocates [3] identified by Maunder et al. [1] provided insight into the exercise capacity of high-level athletes after fat adaptation. Burke et al. [3] found that after 3 weeks of following an LCHF diet, elite-level speed walkers were able to achieve fat oxidation rates of ~ 1.5 g min−1 throughout a simulated endurance event. Similarly, Volek et al. [2] reported peak fat oxidation rates of ~ 1.5 g min−1 in endurance runners who were habituated to the LCHF diet, although average * Christopher C. Webster [email protected] 1
Division of Exercise Science and Sports Medicine, University of Cape Town, Cape Town, South Africa
fat oxidation rates during a 3-h steady-state trial were 1.2 g min−1. It is also important to note that fat-adaptation studies are typically characterised by a wide variety of individual responses, and some individuals in both Burke et al. [3] and Volek et al. [2] had fat oxidation rates exceeding 1.5 g min−1. Additionally, we recently documented the case of an LCHF athlete who fits exactly into the top-amateur category defined by Maunder et al. [1], with Ironman triathlon times of just over 9 h [4]. He had been racing and training on an LCHF diet for 2 years and had achieved these performances without significant carbohydrate supplementation during events. His fat oxidation rates throughout a cycling 100-km time trial in our laboratory were ~ 1.5 g min−1, and we measured fat oxidation rates of ~ 1.7 g min−1 during an incremental exercise test [4]. This case study serves as a practical demon
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