Re-Examining High-Fat Diets for Sports Performance: Did We Call the 'Nail in the Coffin' Too Soon? - PubMed (original) (raw)

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Re-Examining High-Fat Diets for Sports Performance: Did We Call the 'Nail in the Coffin' Too Soon?

Louise M Burke. Sports Med. 2015 Nov.

Abstract

During the period 1985-2005, studies examined the proposal that adaptation to a low-carbohydrate (<25 % energy), high-fat (>60 % energy) diet (LCHF) to increase muscle fat utilization during exercise could enhance performance in trained individuals by reducing reliance on muscle glycogen. As little as 5 days of training with LCHF retools the muscle to enhance fat-burning capacity with robust changes that persist despite acute strategies to restore carbohydrate availability (e.g., glycogen supercompensation, carbohydrate intake during exercise). Furthermore, a 2- to 3-week exposure to minimal carbohydrate (<20 g/day) intake achieves adaptation to high blood ketone concentrations. However, the failure to detect clear performance benefits during endurance/ultra-endurance protocols, combined with evidence of impaired performance of high-intensity exercise via a down-regulation of carbohydrate metabolism led this author to dismiss the use of such fat-adaptation strategies by competitive athletes in conventional sports. Recent re-emergence of interest in LCHF diets, coupled with anecdotes of improved performance by sportspeople who follow them, has created a need to re-examine the potential benefits of this eating style. Unfortunately, the absence of new data prevents a different conclusion from being made. Notwithstanding the outcomes of future research, there is a need for better recognition of current sports nutrition guidelines that promote an individualized and periodized approach to fuel availability during training, allowing the athlete to prepare for competition performance with metabolic flexibility and optimal utilization of all muscle substrates. Nevertheless, there may be a few scenarios where LCHF diets are of benefit, or at least are not detrimental, for sports performance.

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Figures

Fig. 1

Fig. 1

Exercise capacity (time to exhaustion at 62–64 % maximal aerobic capacity, equivalent to ~185 W after 7 days of high-carbohydrate diet followed by 28 days of low-carbohydrate high-fat diet. Data represent mean ± standard error of the mean from five well-trained cyclists (not significantly different), with individual data points represented by O. Redrawn from Phinney et al. [30] CHO carbohydrate

Fig. 2

Fig. 2

Effect of 5 days of adaptation to a low-carbohydrate high-fat diet and 1 day of a high-carbohydrate diet to restore muscle glycogen (FAT-adapt) on rate of carbohydrate oxidation (a) and rate of fat oxidation (b) during cycling at 70 % maximal aerobic capacity compared with control trial (6 days of a high-carbohydrate diet). Data are taken from two studies in which no additional carbohydrate was consumed on the day of a 120-min cycling bout at this same workload (−carbohydrate) [45] or where carbohydrate was consumed before and throughout the 120-min cycling task (+carbohydrate) [41]. Values are mean ± SEM for eight well-trained cyclists at day 1 (baseline), day 6 (after 5 days of low-carbohydrate high-fat diet or 5 days of high-carbohydrate diet) and during 120 min of steady-state cycling on day 7 (following 1 day of high-carbohydrate diet). The adaptation to 5 days of high-fat diet increased fat utilization and reduced carbohydrate utilization during submaximal exercise, persisting despite the restoration of muscle glycogen on day 6 or the intake of additional carbohydrate before/during exercise on day 7. Reproduced from Burke et al. [41] with permission. CHO carbohydrate, HCHO high carbohydrate

Fig. 3

Fig. 3

Power outputs during 1- and 4-km sprints undertaken within a 100-km self-paced cycling time trial after a 6-day high-carbohydrate diet and 5 days of a low-carbohydrate high-fat diet followed by 1 day of a high-carbohydrate diet (fat-adapt) [1]. 100-km total time: 153:10 vs. 156:54 min for carbohydrate vs. FAT-adapt, not significant. Values are means ± standard deviation for eight well-trained cyclists. Power outputs decreased over time in both trials with 4-km sprints (# p < 0.05), but did not differ between trials. However, with the 1-km sprints, mean power was significantly lower after the fat-adaptation treatment (Fat-adapt) compared with the high-carbohydrate diet (*p < 0.05). Reproduced from Havemann et al. [1] with permission. HCHO high carbohydrate

Fig. 4

Fig. 4

Pyruvate dehydrogenase activity in the active form at rest, during 20 min of cycling at ~70 % maximal aerobic capacity followed by a 1-min sprint at 150 % of peak power output after either a 5-day adaptation to a low-carbohydrate high-fat diet followed by a 1-day high-carbohydrate diet (FAT-adapt) or 6 days of a high-carbohydrate diet. Values are means ± standard error of the mean for seven well-trained cyclists. *Different from 0 min, ‡trial effect: HCHO trial > FAT-adapt trial; †time point: HCHO trial > FAT-adapt where significance is set at p < 0.05. Reproduced from Stellingwerff et al. [46] with permission. HCHO high carbohydrate, PDH pyruvate dehydrogenase, PPO peak power output, VO 2 max maximal aerobic capacity

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References

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