This Raises Cortisol, Atrophies Muscle and STOPS Fat Loss When Fasting
Thomas DeLauerPublished on April 27, 2026
Summary authored by editor@wellifi.com
TLDR Summary
To optimize fasting and exercise, avoid high-intensity workouts after 14 hours of fasting and replenish with simple carbohydrates post-workout. Focusing on moderate aerobic and resistance training can help maintain muscle while promoting fat loss.
Key Points
- Avoid high-intensity workouts when fasting for over 14 hours.
- Consume 20-30 grams of carbohydrates after high-intensity workouts to manage cortisol.
- Incorporate resistance training and zone 2 training for optimal fat oxidation.
- Consider blood flow restriction training to promote muscle growth with lighter weights.
The Science of Fasting and Exercise: What You Need to Know
Fasting has become a popular trend for those looking to improve their health, manage weight, and enhance performance. However, as we gain more knowledge from studies and expert experiences, it's clear that there are specific mistakes people often make while fasting—especially regarding exercise. In this blog post, we will explore what types of exercise to avoid when fasting, how to optimize your workouts, what to eat after training, and some effective training strategies.
Understanding the Impact of Fasting on Exercise
As we dive into the physiology of exercise during fasting, it is essential to understand the role of cortisol, the stress hormone, which can significantly impact our body’s performance and recovery. Many people experience symptoms of high cortisol during fasting such as midday fatigue, visceral fat gain, and poor glucose tolerance. Knowing how to manage cortisol is crucial for maximizing the benefits of fasting.
What Not to Do: Avoiding High-Intensity Workouts
A recent study published in Physiology Reports revealed that combining intermittent fasting with high-intensity interval training (HIIT) can lead to elevated cortisol levels, decreased muscle fiber quality, and increased myostatin levels—an inhibitor of muscle growth. This combination can be detrimental, especially if you are fasting for extended periods.
Optimal Training Guidelines
Here are some key guidelines for exercising while fasting:
- If fasting for over 14 hours, avoid high-intensity workouts.
- If fasting for 12 hours or less, you can safely incorporate HIIT.
- For workouts longer than 14 hours, consider switching to low to moderate-intensity exercises.
- Resistance training in a fasted state can be beneficial if done with proper volume and intensity.
What to Eat After Training
After completing a workout during extended fasting, especially high-intensity workouts, it's essential to replenish your body effectively. Consuming 20-30 grams of simple carbohydrates, such as honey, along with protein can help mitigate cortisol spikes and support recovery. This approach helps to balance the hormonal response in a way that prioritizes muscle preservation over fat loss.
Effective Training Strategies in a Fasted State
When training in a fasted state, consider the following strategies:
- Zone 2 Training: Focus on low to moderate-intensity aerobic exercises to maximize fat oxidation.
- Resistance Training: Performing moderate weight lifting in the 6-15 rep range can signal muscle growth without excessive stress.
- Blood Flow Restriction Training: This technique allows you to lift lighter weights while still promoting muscle growth by trapping metabolic byproducts.
Conclusion
Fasting can offer significant health benefits when approached correctly, especially in conjunction with exercise. By avoiding high-intensity workouts during prolonged fasting periods and strategically managing your post-workout nutrition, you can optimize your health and fitness outcomes. Remember to listen to your body and adjust your training as necessary to ensure you maintain a balance between stress and recovery.
For those interested in enhancing recovery and potentially lowering cortisol, consider using a sauna blanket. It provides the benefits of infrared sauna therapy in a convenient and portable format.