Lots of people complain that their athletic performance is reduced with a Low Carbohydrate diet. Dr Volek contends that these issues are due to various reasons:
- Insufficient adaption time – it can take between weeks to months to fully adapt to the ketogenic diet. That is because the body is fueled by ketones rather than glucose.
- Electrolyte Imbalances – The ketogenic diet causes a shift in the body’s electrolytes and requires supplementation. This is even more the case with athletes who sweat a lot.
- Incorrect Amount of Protein – Too little or too much is a problem (between 15% and 25% of calories per day from Protein seems optimal).
See also, the book “The Art and Science of Low Carbohydrate Performance“.
Note that this may be limited to endurance activities rather than higher intensity activities.
…one caveat that anaerobic (ie, weight lifting or sprint) performance is limited by the low muscle glycogen levels induced by a ketogenic diet, and this would strongly discourage its use under most conditions of competitive athletics.
[Added the following studies 2018-02-22]
Here’s another study which has fairly positive results (Nutr Metab (Lond). 2017 Feb 20;14:17. doi: 10.1186/s12986-017-0175-5. eCollection 2017. Impact of a 6-week non-energy-restricted ketogenic diet on physical fitness, body composition and biochemical parameters in healthy adults. Urbain P, Strom L, Morawski L, Wehrle A, Deibert P, Bertz H.). They concluded:
We detected a mildly negative impact from this 6-week non-energy-restricted KD on physical performance (endurance capacity, peak power and faster exhaustion). Our findings lead us to assume that a KD does not impact physical fitness in a clinically relevant manner that would impair activities of daily living and aerobic training. However, a KD may be a matter of concern in competitive athletes.
Another study (J Int Soc Sports Nutr. 2017 Jul 12;14:22. doi: 10.1186/s12970-017-0180-0. eCollection 2017. Ketogenic diet benefits body composition and well-being but not performance in a pilot case study of New Zealand endurance athletes. Zinn C, Wood M, Williden M, Chatterton S, Maunder E.) concluded:
All athletes increased their ability to utilize 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.