Fasted training is becoming increasingly popular, especially among those looking to boost their endurance or lose weight. But is it suitable for everyone? This article highlights key points to consider before trying fasted training.
What is Fasted Training?
Fasted training involves exercising after a period of not eating, like after a night’s sleep. This approach applies to various physical activities, such as running or cycling, with the goal of using the body’s fat stores—primarily from the liver and adipose tissue—for energy. Stored fats are converted into fatty acids, which cells use for energy when carbohydrates, the body’s main energy source, are limited, as during a fast or intense exercise session (1).
However, while this approach enables the use of fat stores, it also has its limitations. After several hours without food, glycogen stores are depleted, forcing the body to draw on its sugar reserves, making it more challenging to maintain optimal performance, especially during prolonged or intense activities. While fasted training may work for certain exercises, it’s not suited for all. Consulting a sports dietitian or nutritionist is recommended to tailor your diet to your specific needs and goals (2).
Key Points Before Trying Fasted Training
Before exploring its benefits and risks, consider the guidance of sports nutrition experts. According to the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine, sufficient carbohydrate intake before exercise helps maintain high glycogen levels, essential for intense and extended activities (2).
Generally, experts advise against prolonged or intense fasted sessions, except under specific, well-monitored conditions, like metabolic adaptation strategies used by elite athletes. Note that more scientific evidence is needed to confirm the definitive effectiveness of fasted training on performance and body composition. A personalized approach guided by a registered dietitian nutritionist is highly recommended.
Potential Benefits of Fasted Training
Some studies suggest that fasted training may offer certain benefits:
1. Encourages Fat Use as an Energy Source
When fasted, glycogen reserves—sugars stored in muscles and the liver—are low, prompting the body to use its fat reserves for energy. This could theoretically support long-term fat loss. However, weight loss largely depends on the overall balance of calories consumed and expended throughout the day (3).
2. Improved Endurance in Athletes
Some research suggests that fasted training might improve the body’s ability to use fat as an energy source during endurance activities. This strategy may benefit prolonged activities like long-distance running or cycling (4). However, this area of research is still evolving, and it’s recommended not to base an entire training regimen solely on fasted sessions.
Risks of Fasted Training
Despite the potential advantages, fasted training also presents some significant risks:
1. Reduced Performance
Without fuel, it may be more difficult to maintain a high intensity, potentially decreasing performance during exercises that require power or speed, such as weightlifting or sprinting (2).
2. Increased Risk of Injury
With low energy levels, muscles may fatigue more quickly, increasing the risk of injuries. Concentration and coordination may also be compromised (2).
3. Loss of Muscle Mass
When glycogen stores are low, the body prioritizes using fat reserves as an energy source. However, if fat stores are insufficient or protein intake is not rapidly replenished post-exercise, the body may turn to muscle proteins to sustain energy levels. Over time, this could lead to muscle loss, particularly if fasted training is done regularly without adequate recovery (2).
The Importance of Recovery After Fasted Training
After a fasted workout, recovery is crucial to allow the body to recuperate effectively. Since glycogen stores are depleted during exercise, it’s essential to replenish them by consuming carbohydrates soon after the session. This helps restore energy and prepares muscles for future exertion.
Including protein in your post-workout meal aids in muscle repair, with average daily protein needs for athletes ranging from 1.2 to 2.4 grams per kilogram of body weight, depending on the type of sport and goals (e.g., fat loss or muscle gain) (5). Having a protein-rich snack or meal after fasted training helps support both muscle and energy recovery. It’s also essential to adjust your diet according to the volume and intensity of your workouts.
Protein-Rich Breakfast Ideas After Fasted Training
- Egg, Broccoli, and Turkey Protein Squares: A nourishing, high-protein breakfast.
- Protein Waffles (Low FODMAP): A healthy, delicious breakfast option served with Greek yogurt or a glass of high protein milk.
- Raspberry Cheesecake Cottage Cheese Mousse: Quick to make, high in protein, and refreshing.
- Strawberry and Date Protein Muffins: A satisfying, fibre-rich post-workout snack with Greek yogurt or cheese.
- Protein Breakfast Bars: Make in advance for quick breakfasts throughout the week.
For more ideas on post-workout protein recipes, check out the recipe section on TeamNutrition and use the "sports nutrition" filter or activate a free trial with KoalaPro Premium.
For most people, a light meal or small pre-workout snack (such as a smoothie bowl or a nutritious banana muffin) can help maintain adequate energy levels and enhance overall performance (6).
Is Fasted Training Right for You?
Fasted training may offer benefits, but it’s essential to choose an approach tailored to your needs. Before trying this method, consult a nutrition expert to ensure it aligns with your goals and health. Book an appointment with a sports dietitian nutritionist for personalized advice to optimize performance while safeguarding your well-being.
References
- Ranallo, R.F., Rhodes, E.C. Lipid Metabolism During Exercise. Sports Med 26, 29–42 (1998). https://doi.org/10.2165/00007256-199826010-00003
- Stannard, S. R., & Buckley, A. J. (2013). Effect of fasting on training and performance. Journal of Science and Medicine in Sport, 16(Supplement 1), e80. https://doi.org/10.1016/j.jand.2015.12.006
- Maughan RJ, Fallah J, Coyle EF. The effects of fasting on metabolism and performance, British Journal of Sports Medicine 2010;44:490-494. https://doi.org/10.1136/bjsm.2010.072181
- Howard EE, Margolis LM. Intramuscular Mechanisms Mediating Adaptation to Low-Carbohydrate, High-Fat Diets during Exercise Training. Nutrients. 2020; 12(9):2496. https://doi.org/10.3390/nu12092496
- Examine. (n.d.). Guide to protein intake. Examine.com. https://examine.com/guides/protein-intake/
- Ormsbee MJ, Bach CW, Baur DA. Pre-Exercise Nutrition: The Role of Macronutrients, Modified Starches and Supplements on Metabolism and Endurance Performance. Nutrients. 2014; 6(5):1782-1808. https://doi.org/10.3390/nu6051782
