The ketogenic diet, or keto diet, has surged in popularity, particularly among athletes looking to optimise body composition, improve endurance, and enhance overall performance. However, there is an increasing body of scientific evidence that suggests the keto diet may not be the best choice for athletes focused on performance, speed, and strength.
While the keto diet may be effective for weight loss and certain medical conditions, it could backfire when applied to athletic contexts. This article examines the science behind the keto diet and explores why it may not be ideal for athletes.
Understanding the Keto Diet and Its Impact on Energy Systems
The keto diet is a high-fat, low-carbohydrate diet that forces the body into a state of ketosis, wherein it relies on fat for fuel rather than carbohydrates. This metabolic shift limits glycogen stores, which are the body’s primary source of energy during high-intensity exercise. Since carbohydrates provide rapid fuel for athletic performance, depleting glycogen can have significant impacts on athletes.
Ketosis and Glycogen: Why Carbs Matter for Athletes
Glycogen, stored in muscles and the liver, is crucial for athletic performance, especially in activities requiring short, intense bursts of energy. Research indicates that muscle glycogen stores are highly correlated with endurance capacity and performance in sports that require repeated high-intensity efforts (Cermak & van Loon, 2013).
The keto diet limits glycogen replenishment, which can lead to early fatigue and reduced performance during anaerobic and high-intensity activities, where carbohydrate metabolism is more efficient than fat oxidation (Burke et al., 2017).
In a review conducted by Egan and Zierath (2013), it was shown that muscle glycogen stores play a central role in performance during high-intensity exercise. When glycogen is depleted, athletes may struggle to maintain their performance levels. This is a particularly important consideration for sports that rely heavily on quick energy bursts, such as sprinting, powerlifting, and certain team sports like football and basketball.
The Downside of Low-Carbohydrate Diets for Strength and Power Athletes
A keto diet’s low-carbohydrate nature means that muscle glycogen levels are consistently lower than in athletes consuming a balanced diet. This can impact strength and power athletes significantly. A study published by Helms et al. (2014) found that low-carbohydrate diets may hinder strength training outcomes, especially in individuals who require a high level of anaerobic capacity.
Further, a 2020 study by Shaw et al. examined athletes on a ketogenic diet and found that their power output was compromised, particularly in activities that demand explosive strength. Athletes in power sports often rely on immediate energy sources, which come from carbohydrates, and without adequate glycogen, performance can decline.
Additionally, other studies have shown that following a low-carbohydrate diet can reduce both muscle protein synthesis and muscle repair, which may slow recovery time and affect muscle gain over the long term (Mettler et al., 2010).
The Effect of the Keto Diet on Endurance Athletes
While the keto diet might seem beneficial for endurance athletes due to its emphasis on fat metabolism, the science is mixed. Some studies suggest that endurance athletes may benefit from enhanced fat oxidation; however, this often comes at the expense of speed and overall performance.
Ketones and Endurance: Is Fat Enough?
A study by Burke et al. (2020) found that while keto-adapted athletes were able to maintain steady energy output, they faced challenges with high-intensity efforts and experienced reduced performance compared to carbohydrate-adapted athletes. This is because the body’s process of oxidising fat for fuel is slower than oxidising glycogen. During sustained efforts or intense bouts, athletes on a keto diet were unable to sustain high levels of output, which can be detrimental to performance in competitive scenarios.
A 2019 study by McSwiney et al. highlighted that, while athletes on a keto diet may exhibit increased rates of fat oxidation, they experienced impairments in speed and power. For long-distance events, the lack of carbohydrate intake means that athletes may be unable to respond to pacing changes or complete the final sprint effectively due to lower glycogen availability.
Risks of Reduced Recovery and Increased Muscle Breakdown
Muscle Protein Synthesis: The Role of Insulin and Carbohydrates
One of the keto diet’s significant drawbacks is its impact on muscle recovery and repair. Carbohydrates are essential for muscle protein synthesis, especially in the post-exercise period when muscles require glycogen replenishment for optimal recovery. Insulin, which is stimulated by carbohydrate intake, helps reduce muscle breakdown and enhances the uptake of amino acids into muscle cells (Morton et al., 2015).
Athletes following a keto diet might find that their recovery times are slower, and they experience more soreness. This is corroborated by a study from Volek et al. (2006), which found that low-carbohydrate diets can impede the body’s recovery process. Insufficient carbohydrate intake can impair insulin’s effectiveness in muscle repair, leading to slower recovery times and a potentially higher risk of injury.
Effects on Immune Function and Inflammation
Carbohydrate restriction may also negatively impact immune function and increase inflammation. A study by Nieman et al. (1997) observed that athletes on low-carbohydrate diets exhibited elevated levels of cortisol and inflammation, potentially due to inadequate glycogen stores. This is particularly important for athletes undergoing high-intensity training or competing frequently, as inflammation and cortisol levels impact overall recovery and resilience.
In contrast, moderate to high carbohydrate intake post-exercise has been associated with reduced markers of inflammation and oxidative stress (Gleeson et al., 2011). Athletes on a keto diet might, therefore, experience prolonged inflammation, which can hinder their training progress and contribute to overtraining symptoms.
Adherence Challenges: Practical Considerations for Athletes
Another critical factor is the practical difficulty of sustaining the keto diet, particularly for athletes with high energy demands. Adhering to a diet that is high in fat and low in carbohydrates can be challenging for those with intense training schedules. Furthermore, the keto diet lacks variety and may lead to reduced intake of certain micronutrients vital for athletes.
Nutrient Deficiencies and Long-Term Risks
A study by Phinney et al. (2004) highlighted that prolonged adherence to the keto diet could result in deficiencies in micronutrients such as vitamin C, potassium, magnesium, and calcium. For athletes, these deficiencies could impair performance and increase the risk of injury. For example, inadequate calcium intake can lead to weakened bone health over time, while low magnesium levels can impact muscle function and recovery.
Gastrointestinal Issues and Energy Intake
The keto diet, with its high fat intake, can also lead to gastrointestinal discomfort, which can affect athletic performance. Some athletes may experience nausea, diarrhoea, or constipation, which can disrupt training and competition routines. Moreover, meeting the caloric requirements of an athlete while maintaining the macronutrient ratios of the keto diet can be difficult, which may lead to insufficient energy intake and unintended weight loss, reducing muscle mass and overall athletic performance (Paoli et al., 2012).
Psychological Impacts: The Role of Carbohydrates in Mental Performance
Athletic performance is not solely about physical fitness; mental sharpness and focus are equally important. Carbohydrates play a significant role in supporting cognitive function and mood, as they increase serotonin levels, which are associated with a positive mental state. A 2015 study by Markus et al. demonstrated that low carbohydrate intake can lead to increased perceived effort, making workouts feel more challenging and potentially impacting motivation.
Additionally, athletes who adopt low-carbohydrate diets may experience reduced mental clarity, leading to difficulties with strategy, focus, and decision-making during competition. This is particularly important in sports that require split-second decisions and quick reflexes.
Summary: The Potential Drawbacks of the Keto Diet for Athletes
While the keto diet has benefits in certain contexts, the evidence suggests that it may be less suitable for athletes due to its impact on glycogen stores, muscle recovery, mental focus, and performance. Athletes considering a keto diet should carefully weigh these factors against the demands of their specific sport and consult with a dietitian or sports nutritionist to explore dietary options that better support their performance and recovery needs.
| Key Takeaways |
|---|
| Low glycogen availability may lead to early fatigue in high-intensity sports. |
| Reduced muscle protein synthesis can slow recovery and impair strength gains. |
| Endurance athletes may suffer from reduced speed and high-intensity performance. |
| Increased inflammation and prolonged recovery can impact training progress. |
| Nutrient deficiencies and GI issues can affect overall health and performance. |
| Mental performance may suffer without sufficient carbohydrates, affecting focus and motivation. |
References
Burke, L. M., Hawley, J. A., Wong, S. H. & Jeukendrup, A. E. (2017). Carbohydrates for training and competition. Journal of Sports Sciences, 35(sup1), 29-38.
Cermak, N. M. & van Loon, L. J. C. (2013). The use of carbohydrates during exercise as an ergogenic aid. Sports Medicine, 43(11), 1139-1155.
Egan, B. & Zierath, J. R. (2013). Exercise metabolism and the molecular regulation of skeletal muscle adaptation. Cell Metabolism, 17(2), 162-184.
Gleeson, M., Bishop, N. C., Oliveira, M. & Tauler, P. (2011). Influence of training load on immune function in elite athletes. Journal of Sports Sciences, 29(sup1), S67-S76.
Helms, E. R., Aragon, A. A. & Fitschen, P. J. (2014). Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. Journal of the International Society of Sports Nutrition, 11(1), 20.
Markus, C. R., et al. (2015). Effects of carbohydrate supplementation on perceived exertion and mood. Appetite, 89, 162-168.
McSwiney, F. T., Wardrop, B., Hyde, P. N., Lafountain, R. A., Volek, J. S. & Diulus, C. (2019). Keto-adaptation enhances endurance exercise performance without a diet-glycogen relationship. Medicine & Science in Sports & Exercise, 51(2), 427-435.
Mettler, S., Mitchell, N. & Tipton, K. D. (2010). Increased protein intake reduces lean body mass loss during weight loss in athletes. Medicine and Science in Sports and Exercise, 42(2), 326-337.
Morton, R. W., et al. (2015). Carbohydrate intake and protein synthesis post-exercise. Journal of Applied Physiology, 119(6), 628-636.
Nieman, D. C., et al. (1997). Influence of carbohydrate intake on immune function. American Journal of Clinical Nutrition, 66(2), 505S-512S.
Paoli, A., et al. (2012). Beyond weight loss: a review of the therapeutic uses of very-low-carbohydrate ketogenic diets. European Journal of Clinical Nutrition, 67(8), 789-796.
Phinney, S. D., et al. (2004). The human metabolic response to chronic ketosis without caloric restriction. Metabolism, 53(8), 1022-1028.
Shaw, D. M., et al. (2020). The impact of a ketogenic diet on endurance performance. Journal of Sports Sciences, 38(7), 818-824.
Volek, J. S., et al. (2006). Dietary carbohydrate restriction in active individuals. Journal of Nutrition and Metabolism, 2006(3), 34-39.
image sources
- keto-and-crossfit: Millennial Methods
- Running Female Athlete: Stevie D Photography
