~ Annie Bothma, Elite Athlete, IOPN Performance Sports Nutritionist (EQF Level 7. Masters), Running & Strength Coach
Training in a fasted state, training without eating beforehand, has sparked considerable interest and discussion in fitness and endurance sports circles. The concept is straightforward: working out on an empty stomach prompts the body to rely on fat as its primary energy source, potentially leading to increased fat burning and improved metabolic efficiency. However, the science surrounding fasted training is complex, with various advantages and risks, particularly for female athletes.
The Science Behind Fasted Training
Research suggests that fasted training can indeed increase lipolysis (fat breakdown) and fat oxidation during exercise, which some athletes may leverage to enhance endurance by improving their ability to use fat as a fuel source. Studies like those by Zouhal et al. (2020) highlight these metabolic adaptations. However, the impact on actual performance is mixed. While some studies report no significant performance improvements, others, such as Levy & Chu (2019), indicate potential detriments to high-intensity performance.
Fasted training poses greater risks for female athletes due to hormonal differences, potentially worsening energy deficits and causing issues like menstrual dysfunction, decreased bone density, and impaired recovery (Mandal et al., 2022).
What Does the Science Say?
Here are four areas of concern with fasted training that athletes should consider before heading out the door with an empty fuel tank:
1. Physiological Adaptations and Performance
Fasted training can increase lipolysis (fat breakdown) and fat oxidation during exercise, which some athletes may utilize to enhance their endurance by improving their ability to use fat as a fuel source (Zouhal et al., 2020). However, the benefits on actual performance outcomes are mixed, with some studies indicating no significant performance improvements, while others suggest potential detriments to high-intensity performance (Levy & Chu, 2019).
2. Impact on Female Athletes
Female athletes might be more vulnerable to the adverse effects of fasted training due to hormonal differences, which could affect their metabolic responses to fasting. There is a concern that fasted training could exacerbate energy deficits, leading to negative outcomes such as menstrual dysfunction, decreased bone density, and impaired recovery over the long run (Mandal et al., 2022).
3. Potential Risks for RED-S
The energy restriction associated with fasted training could be harmful, particularly if not carefully managed. For female athletes, inadequate energy intake can result in the Female Athlete Triad, characterized by energy deficiency, menstrual disturbances, and decreased bone mineral density (Kobelkova et al., 2022). Chronic low energy availability over the long term could lead to RED-S (Relative Energy Deficiency in Sport) in both male and female athletes, a syndrome that negatively impacts nearly every system in the body. This makes fasted training potentially harmful, especially if it leads to prolonged caloric deficits.
4. Psychological and Cognitive Effects
Fasted training can lead to increased perceptions of fatigue and lower cognitive performance during exercise, which may impair training quality and consistency, particularly in more complex or skill-based sports (Chérif et al., 2015).
Practical Advice: How to Fuel Effectively Before Training
Given the potential risks of fasted training, particularly for performance and health, it’s often more beneficial for athletes to fuel adequately before their workouts. Proper fueling can enhance energy levels, improve recovery, and reduce the risk of injury, ultimately leading to better training adaptations and overall performance.
Here are some practical guidelines for pre-training fueling, tailored to the intensity and duration of your workout, along with multiple snack options to choose from:
Low to Moderate Intensity Exercise (< 60 minutes)
For shorter sessions, focus on quick, easy-to-digest carbs with a small amount of protein or fat. Each snack option provides roughly 30-40g of carbohydrates, depending on the brand of products you choose.
Slice of white toast with 1 tbsp jam
A medium-sized banana with 1 tbsp peanut butter
Two rice cakes with 1 small banana and 1 tbsp almond butter
A cup of hard pretzels with a piece of low-fat string cheese (30g)
A cup of low-fat yogurt with 1 cup berries and 1 tbsp honey
Medium Long Run or Workout (> 60 minutes)
For longer or more intense sessions, a slightly larger snack will help sustain your energy levels. Each snack option provides roughly 50-60g of carbohydrates, depending on the brand of products you choose.
Two slices of white toast with 1 medium banana and 1 tbsp peanut or almond butter
Two slices of white toast with 1 tbsp jam or maple syrup and 1 tbsp peanut butter
English muffin with 1 tbsp almond butter and 1 tbsp honey
Hot cross bun with 1 tbsp cream cheese
Oatmeal (40g before cooking) with 2 tbsp raisins and a few almonds and cinnamon
Plain bagel with 2 tbsp low-fat cream cheese
Long Run or Training Session (> 90 minutes)
For extended sessions, a more substantial snack is required to fuel your body adequately and maintain performance. Each snack option provides roughly 70+g of carbohydrates, depending on the brand of products you choose.
Two slices of white toast with 1 tbsp jam or maple syrup, 1 tbsp peanut butter, and a banana on the side
Two slices of white toast with 1 medium banana, 1 tbsp peanut or almond butter, plus 500ml sports drink
Plain bagel with 2 tbsp low-fat cottage cheese and 1 tbsp honey
Two hot cross buns with 2 tbsp low-fat cream cheese
Two English muffins with 2 tbsp almond butter and 1 tbsp honey
Plain bagel with 2 tbsp peanut butter and 1 medium-sized banana
Oatmeal (80g before cooking) with 1/2 cup blueberries, 1 tbsp maple syrup, and a few almonds
Conclusion
While fasted training may offer some metabolic benefits, the research suggests it doesn’t necessarily improve performance and could pose significant risks, especially for female athletes. Instead, fueling properly before your workouts can help you train harder, recover faster, and stay healthier in the long run.
By fueling effectively, you can unlock your full athletic potential and achieve your goals safely and efficiently!
If you’re unsure about how to fuel your training sessions properly or need personalized advice, I’m here to help. Let’s work together to tailor your nutrition and maximize your performance.
Contact me at anniesathletes@gmail.com for more information.
Follow @annies_athletes on Instagram for more content like this.
Resources
Zouhal, H., Saeidi, A., Salhi, A., Li, H., Essop, M., Laher, I., Rhibi, F., & Ben Abderrahman, A. (2020). Exercise Training and Fasting: Current Insights. Open Access Journal of Sports Medicine, 11, 1-28.
Levy, E., & Chu, T. (2019). Intermittent Fasting and Its Effects on Athletic Performance: A Review. Current Sports Medicine Reports, 18(7), 233-239.
Mandal, S., Simmons, N., Awan, S. A. A., Chamari, K., & Ahmed, I. (2022). Intermittent fasting: Eating by the clock for health and exercise performance. BMJ Open Sport & Exercise Medicine, 8(1), e001170.
Kobelkova, I., Korosteleva, M., & Kobelkova, M. (2022). Impact of Fasting on the Health and Performance of the Athlete. Journal of Applied Sports Science, 4(3), 45-52.
Chérif, A., Roelands, B., Meeusen, R., & Chamari, K. (2015). Effects of Intermittent Fasting, Caloric Restriction, and Ramadan Intermittent Fasting on Cognitive Performance at Rest and During Exercise in Adults. Sports Medicine, 46, 35-47.
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