Krogh and Lindhardt (1920) were among the first researchers to recognize the importance of carbohydrates as fuel during exercise itself.
In their research, subjects who consumed a high-fat diet (bacon, butter, etc...) reported different symptoms of fatigue that dissipated when they introduced foods rich in carbohydrates. In later studies, Levine, Gordon, and Derick (1924) measured the blood glucose of different runners in the Boston Marathon in 1923 and saw glucose levels drop after competing.
They suggested that this decrease was related to fatigue and decreased athletic performance. To test this hypothesis, a year later they encouraged many of these participants to consume carbohydrates during the race (sweets), this strategy curiously prevented hypoglycemia and improved sports performance.
In the late 1960s, Scandinavian scientists Bergström et al. (1966) introduced muscle-biopsy methods and demonstrated the fundamental role of muscle glycogen (diets high in carbohydrates = higher glycogen content).
Currently the glycogen particle is known not only for being found in muscle tissue but also in many other tissues (liver, brain, kidneys...) and in different compartments at the cellular level with different functions. That is why it is not only an energy store but also a cellular sensor and regulator of various signaling pathways, oxidative phenotype, autophagy, cortisol, appetite (hepatic glycogen) and even muscle contraction, with intramyofibrillary glycogen being related to the outflow of calcium from the sarcoplasmic reticulum and muscle fatigue.
Role of glycogen availability as an appetite regulator. Gonzalez et al., 2019
Although all this is well known, the diet high in fat in performance has been gaining a lot of popularity within social networks, most of the time because of extrapolating data from studies of short duration, dubious methodology or suboptimal intensities.
Claiming that a high-fat diet by causing increased fat oxidation and contribution to energy metabolism (unlimited energy) leading to a saving of glycogen stores (a low-carb, high-fat ketogenic diet "K-LCHF" can achieve a substantial ~200% increase in peak fat oxidation rates during exercise in endurance-trained athletes ~1.5 g.min-1 to ~ 70% of maximum aerobic capacity).
In the long term, although high-fat diets may induce certain persistent enzymatic adaptations in skeletal muscle favoring fat oxidation, the effects on performance may not be ideal. This is because an increase in fat oxidation is usually mistakenly interpreted as a synonym for improved performance. Although precisely the possible negative effects on performance in athletes using a high-fat diet are not caused by the loss of muscle glycogen per se (up to a certain threshold) but by a suboptimal adaptation to training (by failing to train at the same intensity or maintain the same weekly volume, week after week) worsening the use of certain key enzymes involved in the proper functioning of glycolytic metabolism during competition, where the relative and absolute intensity is surely not moderate or low.
Physiological adaptations of the ketogenic diet – low-carb/high-fat over time Burke., 2020
The acute effect on bone metabolism (increasing resorption and decreasing its metabolism/remodeling) is also known regardless of energy availability, only reducing the carbohydrate content in the periworkout. There are even current studies where they prove that higher carbohydrate intakes per hour (120 g/h) during mountain marathon could limit exercise-associated muscle damage, improve recovery and decrease internal load compared to conventional CHO intakes of 60 and 90 g/h. The authors themselves conclude that the effects of this higher CHO intake (120 g/h) compared to the recommended amount (90 g/h) could possibly be a novel and more suitable strategy to optimize performance in physiologically and metabolically demanding exercises, such as mountain marathons and ultraendurance events.
In fact, during the implementation of poorly planned nutritional periodization strategies (train low/compete high). There are authors who value the deleterious effect that this can have being linked to low energy availability in sport (RED-S) in the long term with all its consequences on health and/or sports performance.
Concluding with this entry that would give for a hundred doctoral theses and that we could not summarize even in a thousand revisions. To quote Louise Burke in her latest review "The availability and ability to use all muscle fuels to meet the specific demands of exercise" is the Holy Grail for high-performance endurance athletes, which explains the ongoing fascination with strategies to improve the utilization of unlimited energy stores (fats).
There is strong evidence that adaptation to an LCHF creates substantial cellular changes to increase fat mobilization, transport, absorption, and oxidation during exercise, although these strategies can also worsen the oxidation of substrates such as carbohydrates that need to be repositioned for proper functioning and improved performance during high intensities.
In high-level athletes, considerable individual variability is observed, but 3-4 weeks of K-LCHF preserves moderate-intensity exercise capacity and performance. Performance from higher-intensity resistance exercise (> 80% VO 2 max) is compromised, possibly due to the higher oxygen cost of producing energy from lipids.
Finally, the optimal adaptation period is in current controversy; Substantial changes in substrate utilization are likely to occur within 5-10 days. Claims that longer adaptation (> 3-4 months) to K-LCHF create additional changes in substrate utilization and improvement in strength performance are currently unsubstantiated and require further research.
Although the hypothesis that chronic high-fat diets can increase the ability to oxidize fat while improving performance during competition is an attractive idea, little evidence indicates that such a hypothesis is true.
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AUTHOR:
Marcos Rueda Córdoba
Dietitian-nutritionist at Myosport Clinic and The Strength Society
Instagram: @marcosnutrition
Bibliography
- Burke, L. M. (2020). Ketogenic low CHO, high fat diet: the future of elite endurance sport?. The Journal of Physiology.
- Murray B, Rosenbloom C. Fundamentals of glycogen metabolism for coaches and athletes. Nutr Rev. 2018;76(4):243–59
- Diaz‐Lara, F. J., Botella, J., & Reisman, E. (2020). Are enhanced muscle adaptations associated with carbohydrate restriction regulated by absolute muscle glycogen concentration?. The Journal of Physiology, 598(2), 221-223.
- Hammond, K. M., Sale, C., Fraser, W., Tang, J., Shepherd, S. O., Strauss, J. A., … & Stewart, C. (2019). Post‐exercise carbohydrate and energy availability induce independent effects on skeletal muscle cell signalling and bone turnover: implications for training adaptation. The Journal of physiology, 597(18), 4779-4796.
- Viribay A, Arribalzaga S, Mielgo-ayuso J, Castañeda-babarro A. Effects of 120 g / h of Carbohydrates Intake during a Mountain Marathon on Exercise-Induced Muscle.
- Heikura IA, Burke LM, Hawley JA, Ross ML, Garvican-Lewis L, Sharma AP, et al. A Short-Term Ketogenic Diet Impairs Markers of Bone Health in Response to Exercise. Front Endocrinol (Lausanne). 2020;10(January):1–10.
- Jeukendrup, A., & Gleeson, M. (2018). Sport nutrition. Human Kinetics.
- Mujika I. Case study: Long-term low-carbohydrate, high-fat diet impairs performance and subjective well-being in a world-class vegetarian long-distance triathlete. Int J Sport Nutr Exerc Metab. 2019;29(3):339–44.
- Hearris MA, Hammond KM, Fell JM, Morton JP. Regulation of muscle glycogen metabolism during exercise: Implications for endurance performance and training adaptations. Nutrients. 2018;10(3):1–21.
- Mata-ordoñez F, Grimaldi-puyana M, Jesús A. Reposición del Glucógeno Muscular en la Recuperación del Deportista Replenishment of muscle glycogen in the recovery of the athlete. 2019;(February).
