¿LOW CARB AND ENDURANCE PERFORMANCE?
Krogh and Lindhart (1920) were among the first researchers to recognize the importance of carbohydrates as fuel during exercise itself.
In their research, subjects consuming a high-fat diet (bacon, butter, etc …) reported different symptoms of fatigue that dissipated when introducing foods rich in carbohydrates. In subsequent studies, Levine, Gordon, and Derick (1924) measured the blood glucose of different correctors of the Boston Marathon in 1923 and saw how glucose levels decreased after competing.
In this way they suggested that this decrease was related to fatigue and decreased sports performance. To test these hypotheses, a year later they encouraged many of these participants who consumed carbohydrates during the race (sweets), this curiously pre-hypoglycemic strategy and improved sports performance.
In the years following the late 1960s, Scandinavian scientists Bergstrom et al., (1966) introduced muscle biopsy methods finding the fundamental involvement of muscle glycogen (high carbohydrate diets = higher glycogen content).
Currently the glycogen particle is known not only for being found in muscle tissue but in many other tissues (liver, brain, kidneys …) and in different compartments at the cellular level with different functions. That is why, so it is not just an energy store but a cellular sensor and regulator of various signaling pathways, oxidative phenotype, autophagy, cortisol, appetite (liver glycogen) and even muscle contraction, relating intramiofibrillary glycogen with Calcium leakage from the sarcoplasmic reticulum and muscle fatigue.
Although all this is well known, the high-fat diet in performance has been booming quite a bit within social networks, most of the time due to extrapolating data from short-term studies, questionable methodology or suboptimal intensities.
Claiming that a high-fat diet by causing increased fat oxidation and its contribution to energy metabolism (unlimited energy) leading to savings in glycogen stores (a low-carbohydrate, high-fat keto diet can “K-LCHF” achieve a significant ~ 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 enzyme adaptations in skeletal muscle favoring fat oxidation, the performance effects may not be optimal. This is because an increase in fat oxidation is normally mistakenly interpreted as a synonym for improved performance. Although specifically the possible negative effects on performance in athletes who use 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 not being able to train 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 may be unmoderated or low.
The effect of acute form on bone metabolism (increased resorption and decreased metabolism / remodeling) is also known, specifically on energy availability, only reducing the carbohydrate content in the perientrene. There are even current studies that show that higher intakes of carbohydrates per hour (120 g / h) during the mountain marathon could limit exercise-related muscle damage, improve recovery and decrease internal load compared to CHO calculations. 60 and 90 g / h. Concluding by the authors themselves that the effects of this higher intake of CHO (120 g / h) compared to the recommended amount (90 g / h) could possibly be a novel and more appropriate strategy to improve performance in physiological exercises and metabolically demanding, such as mountain marathons and ultraendurance events.
The effect of acute form on bone metabolism is also known (increasing resorption and decreasing its metabolism / remodeling) regardless of energy availability, only reducing the content of carbohydrates in the perientrene. There are even current studies that show that higher intakes of carbohydrates per hour (120 g / h) during the mountain marathon could limit exercise-related muscle damage, improve recovery and decrease internal load compared to conventional CHO intakes. 60 and 90 g / h. Concluding by the authors themselves that the effects of this higher intake of CHO (120 g / h) compared to the recommended amount (90 g / h) could possibly be a novel and more appropriate strategy to optimize performance in physiological exercises and metabolically demanding, 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 a 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 reviews. Quoting Louise burke in her latest review “The availability and ability to use all muscle fuels to meet the specific demands of exercise” metabolic flexibility “is about the Holy Grail for high performance endurance athletes, which explains the fascination It continues for strategies to improve the use of unlimited energy reserves (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 may also worsen the oxidation of substrates such as carbohydrates that they need to be repositioned for proper operation and performance improvement during high intensities.
In high-level athletes, considerable individual variability is observed, but 3-4 weeks of K-LCHF retains the capacity and performance of moderate intensity exercise. The performance of higher intensity endurance exercise (> 80% VO2 max) is compromised, possibly due to the higher cost of oxygen from the production of energy from lipids.
Finally, the optimal adaptation period is currently in 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 resistance performance are currently unfounded and require further investigation.
Although the hypothesis that chronically 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.