High Rates of Fat Oxidation Induced by a Low-Carbohydrate, High-Fat Diet, Do Not Impair 5-km Running Performance in Competitive Recreational Athletes.

Dec 13, 2019Journal of sports science & medicine

High Fat Burning from a Low-Carb, High-Fat Diet Does Not Hurt 5-km Running in Competitive Recreational Athletes

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Abstract

Performance in 5-km running time trials was significantly slower on a low-carbohydrate, high-fat diet compared to a high-carbohydrate, low-fat diet during the initial trial.

Performance during maximal exercise tests remained unchanged regardless of diet.
Carbohydrate oxidation contributed 94% of energy on the high-carbohydrate, low-fat diet and only 65% on the low-carbohydrate, high-fat diet.
No significant performance differences were observed in subsequent 5-km running time trials after the initial trial.
The findings suggest that adapting to a low-carbohydrate diet may not impair performance in competitive recreational athletes exercising at high intensities.

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A common belief is that high intensity exercise (>60%VO) is best sustained by high rates of carbohydrate oxidation. The belief is based, in part, on an idea developed by Krogh and Lindhard in 1920. In the 100 years since, few studies have tested its validity. We tested the null hypothesis that performance in competitive recreational athletes exercising at >80% VO, during simulated 5-km running time trials (5KTT) would be impaired during a 6-week period of adaption to a low-carbohydrate, high-fat (LCHF) diet, compared to their performances when they ate a diet higher in carbohydrate and lower in fat (HCLF). Seven male athletes (age 35.6 ± 8.4 years, height 178.7 ± 4.1 cm, weight 68.6 ± 1.6 kg) completed two maximal exercise (VO) tests (Day 1 and 39) and four 5KTT (Day 4, 14, 28, and 42) in a fasted state during two 6-week periods when they ate either a HCLF or a LCHF diet, in a randomized counterbalanced, crossover design. Exercise performance during the VOtests was unchanged on either diet (p = 0.251). Performance in the initial 5KTT was significantly slower on the LCHF diet (p = 0.011). There were no diet-related performance differences in the remaining three 5KTT (p > 0.22). Subjects exercised at ~82%VO. Carbohydrate oxidation provided 94% of energy on the HCLF diet, but only 65% on the LCHF diet. 5KTT performance at ~82%VOwas independent of the runners' habitual diet. The HCLF diet offered no advantage over a diet with a high-fat content. Since these athletes run faster than 88% of recreational distance runners in the United States (U.S.), this finding may have wide general application. 2max2max2max2max2max2max

Abstract

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