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.

Abstract: We 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, V̇O2 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% V̇O2 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 V̇O2 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 V̇O2 peak , adaptation to the topical LCHF diet negated performance benefits in elite endurance athletes, in part due to reduced exercise economy.

Keywords: athletic performance; ketogenic diet; sports nutrition.

Figure 1. Overview of 3‐week training–diet intervention and testing blocks in elite race walkers undertaking high carbohydrate availability (HCHO, n = 9), periodised carbohydrate availability (PCHO, n = 10) or ketogenic low carbohydrate, high fat (LCHF, n = 10) diet

Figure 2. Oxygen uptake during graded economy test at second stage approximating 50 km race speed (A, ml kg⁻¹ min⁻¹ and B, % V˙O2 peak ) and fourth stage approximating 20 km race speed (C, ml kg⁻¹ min⁻¹ and D, % V˙O2 peak ) in elite race walkers pre‐ and post‐3 weeks of intensified training and high carbohydrate availability (HCHO, n = 9), periodised carbohydrate availability (PCHO, n = 10), or ketogenic low carbohydrate, high fat (LCHF, n = 10) diets

^*Significantly different from pre‐treatment (P <  0.01).

Figure 3. Blood metabolite concentrations (blood glucose (mmol l⁻¹, A), blood lactate (mmol l⁻¹, B) and blood ketones (β‐hydroxybutyrate, mmol l⁻¹, C)) during graded economy test and test for peak aerobic capacity in elite race walkers pre‐ and post‐3 weeks of intensified training and high carbohydrate availability (HCHO, n = 9), periodised carbohydrate availability (PCHO, n = 10), or ketogenic low carbohydrate high fat (LCHF, n = 10) diets

^*Significantly different from pre‐treatment (P <  0.01).

Figure 4. Race times for IAAF sanctioned 10 km race walk events in elite race walkers undertaken pre‐ (Race 1) and post‐ (Race 2) 3 weeks of intensified training and high carbohydrate availability (HCHO, n = 9), periodised carbohydrate availability (PCHO, n = 8), or ketogenic low carbohydrate, high fat (LCHF, n = 9) diets

^*Significantly different from pre‐treatment (P <  0.01).

Figure 5. Oxygen uptake (A, ml kg⁻¹ min⁻¹; and B, % V˙O2 peak ) and substrate utilisation (C, rates of carbohydrate (CHO) oxidation in g min⁻¹; and D, rates of fat oxidation in g min⁻¹) during 25 km standardised long walk in elite race walkers pre‐ and post‐3 weeks of intensified training and high carbohydrate availability (HCHO, n = 8), periodised carbohydrate availability (PCHO, n = 9) or ketogenic low carbohydrate, high fat (LCHF, n = 10) diets

^*Significantly different from pre‐treatment (P <  0.01); †significant change over the 25 km walking session.

Figure 6. Blood metabolite concentrations (blood glucose (mmol l⁻¹, A), blood lactate (mmol l⁻¹, B) and blood ketones (β‐hydroxybutyrate, mmol l⁻¹, C) during 25 km standardised long walk in elite race walkers pre‐ and post‐3 weeks of intensified training and high carbohydrate availability (HCHO, n = 8), periodised carbohydrate availability (PCHO, n = 9), or ketogenic low carbohydrate, high fat (LCHF, n = 10) diets

^*Significantly different from pre‐treatment (P <  0.01).