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Ketogenic Diet Benefits Body Composition and Well-Being but Not Performance in a Pilot Case Study of New Zealand Endurance Athletes

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Ketogenic Diet Benefits Body Composition and Well-Being but Not Performance in a Pilot Case Study of New Zealand Endurance Athletes

Caryn Zinn et al. J Int Soc Sports Nutr.

Abstract

Background: Low-carbohydrate, high-fat and ketogenic diets are increasingly adopted by athletes for body composition and sports performance enhancements. However, as yet, there is no consensus on their efficacy in improving performance. There is also no comprehensive literature on athletes' experiences while undertaking this diet. The purpose of this pilot work was two-fold: i. to examine the effects of a non-calorie controlled ketogenic diet on body composition and performance outcomes of endurance athletes, and ii. to evaluate the athletes' experiences of the ketogenic diet during the 10-week intervention.

Methods: Using a case study design, five New Zealand endurance athletes (4 females, 1 male) underwent a 10-week ketogenic dietary intervention. Body composition (sum of 8 skinfolds), performance indicators (time to exhaustion, VO2 max, peak power and ventilatory threshold), and gas exchange thresholds were measured at baseline and at 10 weeks. Mean change scores were calculated, and analysed using t-tests; Cohen's effect sizes and 90% confidence limits were applied to quantify change. Individual interviews conducted at 5 weeks and a focus group at 10 weeks assessed athletes' ketogenic diet experiences. Data was transcribed and analysed using thematic analysis.

Results: All athletes increased their ability to utilise fat as a fuel source, including at higher exercise intensities. Mean body weight was reduced by 4 kg ± SD 3.1 (p = 0.046; effect size (ES):0.62), and sum of 8 skinfolds by 25.9 mm ± SD 6.9; ES: 1.27; p = 0.001). Mean time to exhaustion dropped by ~2 min (±SD 0.7; p = 0.004; ES: 0.53). Other performance outcomes showed mean reductions, with some increases or unchanged results in two individuals (VO2 Max: -1.69 ml.kg.min ± SD 3.4 (p = 0.63); peak power: -18 W ± SD 16.4 (p = 0.07), and VT2: -6 W ± SD 44.5 (p = 0.77). Athletes reported experiencing reduced energy levels initially, followed by a return of high levels thereafter, especially during exercise, but an inability to easily undertake high intense bouts. Each athlete reported experiencing enhanced well-being, included improved recovery, improvements in skin conditions and reduced inflammation.

Conclusions: Despite performance decrements and some negative experiences, athletes were keen to pursue a modified low-carbohydrate, high-fat eating style moving forward due to the unexpected health benefits they experienced.

Trial registration: ACTRN: ACTRN12617000613303. Registered 28 April 2017, retrospectively registered.

Keywords: Endurance athletes; LCHF; Low-carbohydrate, high-fat; Performance; Well-being.

Conflict of interest statement

Ethics approval and consent to participate

Ethics was approved by the AUT Ethics Committee (application 15/415).

Consent for publication

All participants provided their consent for their individual data to be published.

Competing interests

The corresponding author, CZ, has co-authored two books called “What The Fat? - Fat’s in, Sugar’s out”, and “What The Fat – Sports performance”. These books were constructed and published after the study was concluded.

Publisher’s Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Figures

Fig. 1
Fig. 1
Pre, and post intervention metabolic efficiency curves for each participant. * PFox: Peak Fat Oxidation (g/min). † Fatmax: Maximum fat oxidation at % WRmax
Fig. 2
Fig. 2
Individual responses and effect sizes of anthropometry and performance variables

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References

    1. Burke LM, Hawley JA, Wong SH, Jeukendrup AE. Carbohydrates for training and competition. J Sports Sci. 2011;29(Suppl 1):S17–S27. doi: 10.1080/02640414.2011.585473. - DOI - PubMed
    1. Lambert EV, Hawley JA, Goedecke J, Noakes T. Nutritional strategies for promoting fat utilization and delaying the onset of fatigue during prolonged exercise. J Sports Sci. 1997;15(3):315–324. doi: 10.1080/026404197367326. - DOI - PubMed
    1. Phinney SD. Ketogenic diets and physical performance. Nutr Metab. 2004;1(1):2. doi: 10.1186/1743-7075-1-2. - DOI - PMC - PubMed
    1. Noakes T, Volek JS, Phinney SD. Low-carbohydrate diets for athletes: what evidence? Br J Sports Med. 2014;48(14):1077–1078. doi: 10.1136/bjsports-2014-093824. - DOI - PubMed
    1. Phinney SD, Bistrian BR, Evans WJ, Gervino E, Blackburn GL. The human metabolic response to chronic ketosis without caloric restriction: preservation of submaximal exercise capability with reduced carbohydrate oxidation. Metab Clin Exp. 1983;32(8):769–776. doi: 10.1016/0026-0495(83)90106-3. - DOI - PubMed
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