Low carbohydrate, high fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers

Abstract

Key points Three weeks of intensified training and mild energy deficit in elite race walkers increases peak aerobic capacity independent of dietary support.Adaptation to a ketogenic low carbohydrate, high fat (LCHF) diet markedly increases rates of whole‐body fat oxidation during exercise in race walkers over a range of exercise intensities.The increased rates of fat oxidation result in reduced economy (increased oxygen demand for a given speed) at velocities that translate to real‐life race performance in elite race walkers.In contrast to training with diets providing chronic or periodised high carbohydrate availability, adaptation to an LCHF diet impairs performance in elite endurance athletes despite a significant improvement in peak aerobic capacity. AbstractWe investigated the effects of adaptation to a ketogenic low carbohydrate (CHO), high fat diet (LCHF) during 3 weeks of intensified training on metabolism and performance of world‐class endurance athletes. We controlled three isoenergetic diets in elite race walkers: high CHO availability (g kg−1 day−1: 8.6 CHO, 2.1 protein, 1.2 fat) consumed before, during and after training (HCHO, n = 9); identical macronutrient intake, periodised within or between days to alternate between low and high CHO availability (PCHO, n = 10); LCHF (< 50 g day−1 CHO; 78% energy as fat; 2.1 g kg−1 day−1 protein; LCHF, n = 10). Post‐intervention, V˙O2 peak 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% V˙O2 peak . However, LCHF also increased the oxygen (O2) cost of race walking at velocities relevant to real‐life race performance: O2 uptake (expressed as a percentage of new V˙O2 peak ) 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 V˙O2 peak , adaptation to the topical LCHF diet negated performance benefits in elite endurance athletes, in part due to reduced exercise economy.

Changes in metabolism but not myocellular signaling by training with CHO-restriction in endurance athletes

“…However, exposure to a variety of different CHO‐ and energy restriction strategies also failed to demonstrate superimposing training effects in a recent comprehensive 3‐week study in highly trained race walkers (Burke et al. ).…”

Communicating Sports Science in the Age of the Twittersphere

“…Just before the preparation of this commentary, my research group was rewarded with the acceptance of a manuscript summarizing the effect of the low carbohydrate, high fat diet (LCHF) on the economy and performance of endurance exercise in elite race walkers (Burke et al 2017). This study achieved a number of Complex issues reduced to "sound bites"…”

Energy Balance During A Self-sufficient, Multistage Ultramarathon

“…Consequently, ultra-endurance athletes wishing to experiment with a LCHF diet should proceed with caution, particularly if the event involves periods of high-intensity (>75% VO 2max ) exercise (e.g. hill climbing), as a chronic LCHF diet can potentially lead to a reduction in exercise performance (Burke et al, 2017;Zajec et al, 2014) and potentially impair metabolic flexibility (i.e. the capacity to oxidize carbohydrates) (Burke & Kiens, 2006).…”