Low Carbohydrate, High Fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers
We investigated the effects of adaptation to a ketogenic low-carbohydrate (CHO), high-fat diet (LCHF) during 3 wk of intensified training on metabolism and performance of world-class endurance athletes. We controlled three isoenergetic diets in elite race walkers: High CHO availability (8.6 g.kg−1.d−1 CHO, 2.1 g.kg−1.d−1 protein; 1.2 g.kg−1.d−1 fat) consumed before/during/after training (HCHO, n = 9): identical macronutrient intake, periodised within/between days to alternate between low and high CHO availability (PCHO, n = 10); LCHF (<50 g.d−1 CHO; 78% energy as fat; 2.1 g.kg−1.d−1 protein; LCHF, n = 10). Post-intervention, VO2peak during race walking increased in all groups (P < 0.001, 90%CI: [2.55 - 5.20%]). LCHF was associated with markedly increased rates of whole-body fat oxidation, attaining peak rates of 1.57 ± 0.32 g.min−1 during 2 h of walking at ∼80%VO2peak. However, LCHF also increased the oxygen (O2) cost of race walking at velocities relevant to real-life race performance: O2 uptake (expressed as % of new VO2peak) at a speed approximating 20 km race pace was reduced in HCHO and PCHO (90%CI:[−7.047;−2.55] and [−5.18;−0.86], respectively, but was maintained at pre-intervention levels in LCHF. HCHO and PCHO groups improved times for 10 km race walk: 6.6% (90% CI: [4.1; 9.1%]) and 5.3% [3.4; 7.2%], with no improvement (−1.6% [−8.5; 5.3%] for the LCHF group. In contrast to training with diets providing chronic or periodised high-CHO availability, and despite a significant improvement in VO2peak, adaptation to the topical LCHF diet negated performance benefits in elite endurance athletes, in part, due to reduced exercise economy.
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Autor / Fonte:Louise M Burke, Megan L Ross, Laura A Garvican-Lewis, Marijke Welvaert, Ida A Heikura, Sara G Forbes, Joanne G Mirtschin, Louise E Cato, Nicki Strobel, Avish P Sharma, John A Hawley Journal of Physiology 2016 December 23