Ketogenic diet and metabolic flexibility

As we have discussed previously in other guides , nutritional periodization is key to maximizing athletic performance. Another way to train lightly (low-carb) would be to eliminate carbohydrates from the diet and follow a long-term, low-carb, high-fat diet. In the 1920s, it was demonstrated that reducing carbohydrate intake and increasing fat intake would result in higher rates of fat oxidation (1) . However, it was also observed that subjects felt more fatigued (1) and exercise capacity was reduced with this practice (2). Burke and colleagues (3 , 4 , 5) conducted a series of studies on short-term, low-carb, high-fat diets, and one of their observations was that just 5 days on a low-carb, high-fat diet already showed some adaptations to that diet that could not be completely reversed by replenishing muscle glycogen stores. The enzymes involved in fat oxidation increased, and fat oxidation increased (3) . In none of the studies, however, were improved effects on performance observed (4,5). When athletes trained for a longer period of time (7 weeks) on either a high-fat (62% fat, 21% carbohydrate) or high-carbohydrate (20% fat, 65% carbohydrate) diet, both groups were found to improve with training, but the training effects were more pronounced in the high-carbohydrate group.

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There is one study that is always cited as evidence of the benefits of a ketogenic diet. In the 1980s, a study with five subjects showed that a ketogenic diet, containing less than 20 g of carbohydrates per day, over a prolonged period (4 weeks) resulted in hyperketonemia and increases in fat oxidation (6) . In this study, exercise capacity was only tested at low intensity and showed a high degree of variation both between and within subjects. On average, there was no difference in exercise capacity before and after the ketogenic diet. As expected, fat oxidation increased, and some muscle adaptations occurred.

A study by Stellingwerff et al. (7) demonstrated that although a high-fat diet increases fat oxidation, perhaps by increasing enzyme activity related to fat metabolism, it may reduce enzyme activity related to carbohydrate metabolism. Thus, while many studies observed improvements in HAD, for example, Stellingwerff et al. (7) demonstrated compromised pyruvate dehydrogenase activity. Therefore, it may be that fat oxidation increases, at least in part, as a result of the inability to utilize carbohydrates. Because carbohydrates are important substrates for high-intensity exercise, such adaptations would be undesirable. In fact, a carefully controlled study by Burke et al. (8) demonstrated that there were no benefits of a ketogenic diet versus a high-carbohydrate diet, or a mixed approach (more or less carbohydrates depending on training) in elite endurance athletes.

In fact, high-intensity exercise performance did not improve with 3 weeks of intense training in the ketogenic diet group (−1.6%), while athletes who consumed the other diets achieved substantial improvements in performance (6.6% in the high-carbohydrate group and 5.5% in the mixed group).

The ketogenic diet has received considerable attention in the popular press, and many claims have been made recently. However, it is important to realize that, to date, no study has demonstrated the performance benefits of a ketogenic diet, including the initial study that is often referenced (6). Therefore, there is currently no data on ketogenic diets in athletes on which to base performance claims.

IS THE USE OF CARBOHYDRATES IMPORTANT DURING SPORTS?

Bergman and colleagues (9 , 10) trained nine amateur and professional male subjects for 9 weeks during 1 hour of cycling at two exercise intensities beforehand (45 and 65% of VO2max). They demonstrated that for both amateur and professional athletes, their main oxidation substrate was carbohydrates, not fats.

In 2000, a comprehensive review of the available literature on athletes' dietary practices was conducted to address some of the challenges surrounding athletes' self-chosen carbohydrate intakes (11). Male endurance athletes generally consumed daily carbohydrate intakes of 5–7 g/kg/day for general training needs, with some evidence that this was higher than that observed among athletes in previous studies (11). Some research related to competition nutrition, periods of increased training, or elite athletes such as Kenyan long-distance runners (12) or Tour de France cyclists (13) has reported higher intakes of 7–12 g of carbohydrates/kg/day for specific periods. These carbohydrate intakes, and the concomitant moderate fat intakes, are in line with the sports nutrition guidelines of the corresponding era (14). It should be noted that, unlike male endurance athletes, some women are less likely to meet the recommended carbohydrate intake guidelines, primarily due to their relatively lower energy intake (11). Despite the potential limitations of dietary survey techniques in assessing the adequacy of athletes' dietary practices (i.e., potential errors caused by lack of information or insufficient food intake during the survey period), the available data clearly demonstrate that endurance athletes from the 1990s to 2005 consumed high-carbohydrate, low-fat diets.

Official dietary guidelines for athletes have evolved in recent decades to better define the goals and targets for optimal carbohydrate (CHO) intake during training and competition. These guidelines now promote the goal of "high CHO availability" (CHO intake intended to meet the specific substrate needs of training/competition) rather than absolute (daily) CHO intake per se. Furthermore, this goal is aligned with training sessions or events when optimal performance is required, and there is an implicit recognition that higher CHO intakes or high CHO availability may not be necessary during other sessions (15 , 16). In fact, there are evolving dietary periodization practices in which some sessions are deliberately conducted with low CHO availability to promote training adaptations. However, it should be emphasized that these strategies are implemented acutely, periodized to constitute a small proportion of the training program, avoided when high-quality/intensity training outcomes are required, and generally not achieved through the admission of a high-fat diet (17 , 18) , as explained above in the carbohydrate periodization guide.

The core philosophy of undertaking high-quality training and competition with high carbohydrate availability is maintained to promote training adaptations and the optimal use of carbohydrates as a substrate for the brain and central nervous system (16). While data on how highly trained competitive endurance athletes implement such practices are lacking, evidence supports the idea that these athletes freely select carbohydrate-rich or carbohydrate-periodized diets instead of high-fat diets. Such a strategy is essential for maintaining muscle energy stores and meeting the daily demands of strenuous endurance training sessions.

THE EVIDENCE BETRAYS THEM

There are numerous studies that demonstrate to the ketogenic community that the use of fats is much better than the consumption of carbohydrates.

One of the studies known for its use in supporting the ketogenic diet for athletic performance is that of McKenzie and colleagues (19 , 20). This study evaluated changes in muscle glycogen (MG) and triglyceride (MT) concentrations in aerobically conditioned sled dogs during prolonged exercise. The study concluded (read carefully and then tell us what they have in common) that significantly more triglycerides (fats) were used during the first 140 km run compared to the amount used during the last 140 km, suggesting that extramuscular substrates likely play an important role in supporting muscle work in sled dogs undergoing repeated bouts of prolonged exercise. Results from another study of dogs subjected to prolonged submaximal exercise indicated that plasma free fatty acids are the predominant energy substrate used during lower-intensity exercise in this species.

A study of 18 human cyclists who consumed a high-fat diet revealed an increased capacity for fat metabolism and a fourfold decrease in fat utilization during exercise, compared to cyclists who consumed a standard diet; these changes did not negatively impact performance. Furthermore, consuming a high-fat diet has a synergistic effect with conditioning in rats, resulting in greater submaximal running endurance.

As you will see, the common factor is the use of claims with animals, rats, dogs, etc. Furthermore, they are cross-sectional studies, which is observational, so not much data is collected from their daily lives and only post-diet data (without verifying if they actually follow the required diet).

On the other hand, they claim the ketogenic diet is the holy grail of sports nutrition, citing another common study (21) that asserts muscle glycogen can be replenished without carbohydrate intake, solely through fats. In this study, horses fed a high-fat diet showed glycogen replenishment "similar" to that of horses fed a high-carbohydrate diet.

As you can see, their common factor is animals and observational studies to defend the use of fats over the use of carbohydrates.

As you already know, the only way to achieve optimal muscle and liver glycogen replenishment is through the use of post- and intra-exercise carbohydrates with a proper combination of simple and complex carbohydrates. Check out all our muscle glycogen guides to learn more and our products based on current scientific evidence.

Literature

1. Krogh A, Lindhard J. The relative value of fat and carbohydrate as sources of muscular energy. Biochem J. 1920;14:290–363.
2. Christensen EH, Hansen O. Carbohydrate Supplements During and Immediately Post Exercise. Arbeitsfähigkeit und Ernährung. Scand Arch Physiol. 1939;81:160–71.
3. Burke LM, Angus DJ, Cox GR, et al. Effect of fat adaptation and carbohydrate restoration on metabolism and performance during prolonged cycling. J Appl Physiol. 2000;89:2413–21.
4. Burke LM, Hawley JA, Angus DJ, et al. Adaptations to short-term high-fat diet persist during exercise despite high carbohydrate availability. Med Sci Sports Exerc. 2002;34:83–91.
5. Burke LM, Hawley JA. Effects of short-term fat adaptation on metabolism and performance of prolonged exercise. Med Sci Sports Exerc. 2002;34:1492–8.
6. Phinney SD, Bistrian BR, Evans WJ, et al. The human metabolic response to chronic ketosis without caloric restriction: preservation of submaximal exercise capability with reduced carbohydrate oxidation. Metabolism. 1983;32:769–76.
7. Stellingwerff T, Spriet LL, Watt MJ, et al. Decreased PDH activation and glycogenolysis during exercise following fat adaptation with carbohydrate restoration. Am J Physiol. 2006;290:E380–8.
8. Burke LM, Ross ML, Garvican-Lewis LA, et al. Low carbohydrate, high fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers. 2016.
9. Bergman BC, Butterfield GE, Wolfel EE, et al. Evaluation of exercise and training on muscle lipid metabolism. Am J Physiol. 1999;276:E106–17.
10. 10.Bergman BC, Brooks GA. Respiratory gas-exchange ratios during graded exercise in fed and fasted trained and untrained men. J Appl Physiol. 1999;86:479–87.
11. Burke LM, Cox GR, Cummings NK, et al. Guidelines for daily carbohydrate intake: do athletes achieve them? Sports Med. 2001;31:267–99.
12. Onywera VO, Kiplamai FK, Boit MK, et al. Food and macronutrient intake of elite Kenyan distance runners. Int J Sport Nutr Exerc Metab. 2004;14:709–19.
13. Saris WHM, Van Erp-Baart MA, Brouns F, et al. Study on food intake and energy expenditure during extreme sustained exercise: the Tour de France. Int J of Sports Medicine. 1989;10:S26–31.
14. Burke LM, Kiens B, Ivy JL. Carbohydrates and fat for training and recovery. J Sports Sci. 2004;22:15–30.
15. Burke L.M. Re-examining high-fat diets for sports performance: did we call the 'nail in the coffin' too soon? Sports Med. 2015;45.
16. Burke LM, Hawley JA, Wong SH, et al. Carbohydrates for training and competition. J Sports Sci. 2011;29:S17–27.
17. Hansen AK, Fischer CP, Plomgaard P, et al. Skeletal muscle adaptation: training twice every second day vs. training once daily. J Appl Physiol. 2005;98:93–9.
18. Yeo WK, Paton CD, Garnham AP, et al. Skeletal muscle adaptation and performance responses to once a day versus twice every second day endurance training regimens. J Appl Physiol. 2008;105:1462–70.
19. Erica C. McKenzie, Kenneth W. Hinchcliff, Stephanie J. Valberg, Katherine K. Williamson, Mark E. Payton and Michael S. Davis. Assessment of alterations in triglyceride and glycogen concentrations in muscle tissue of Alaskan sled dogs during repetitive prolonged exercise. Volume 69: Issue 8
20. McKenzie, Erica; Holbrook, Todd; Williamson, Kathy; Royer, Christopher; Valberg, Stephanie; Hinchcliff, Ken; jose-cunilleras, eduard; Nelson, Stuart; Willard, Michael; davis, michael. Recovery of Muscle Glycogen Concentrations in Sled Dogs During Prolonged Exercise. Medicine & Science in Sports & Exercise: August 2005 – Volume 37 – Issue 8 – p 1307-1312
21. S. HYYPPä,M. SAASTAMOINEN,A. REETA PÖSÖ. Effect of a post exercise fat-supplemented diet on muscle glycogen repletion. June 10, 2010