Is it a good idea to fast before exercise ?

Fasting before exercise can have benefits, especially if your goal is to burn more body fat. Here's what Andrew Huberman said about it:

1. Fat Oxidation: Training in a fasted state can lead to greater fat oxidation. Studies show that insulin inhibits fat burning, so exercising without eating beforehand can allow for more efficient fat oxidation 1.

2. Duration and Intensity: For moderate intensity exercise, the benefits become significant after about 90 minutes. If you have fasted for at least three hours before exercising, you will burn more fat from the 90-minute point onward compared to if you had eaten within the previous one to three hours 2.

3. General Preference: Andrew Huberman personally prefers doing his cardiovascular and resistance training in a fasted state. This includes drinking water and possibly caffeine, but generally avoiding food intake for about three to ten hours before exercise 3 4.

   
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   Fasted Exercise Insights
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   Fasted Exercise Benefits
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   Fasted Training
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   Training Fasted
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   Fasted or Fed?
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4. Flexibility: Feeding protocols can be highly individual. While some people perform better when fasted, others may need to eat to achieve optimal performance. It’s crucial to find what works best for your body and training regimen, taking care to avoid gastric distress and ensure performance 5.

In summary, training fasted can facilitate more fat burning and may enhance certain health benefits, but individual preferences and tolerances should guide your approach.

Exercising while fasted can have several drawbacks. Here are some key points highlighted by Andrew Huberman and other experts on the Huberman Lab:

1. Impaired Performance: Exercising in a fasted state can sometimes impair performance, particularly for high-intensity activities. If you don't have adequate glucose available, you might not be able to sustain the energy levels needed for optimal performance 1.

2. Increased Stress Levels: Dr. Stacy Sims, a guest on the podcast, mentions that fasted exercise can increase cortisol levels, which might lead to stress imbalances, especially in women. This can impact metabolic flexibility and overall health 2.

3. Cognitive Effects: Fasting can alter perception and cognitive function. While some may experience mental clarity, others might face issues with focus and precision due to lack of glucose, which is the preferred fuel for the brain 3.

   
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   Fasted Exercise Insights
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   Metabolic Flexibility Insights
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   Fasting and Perception
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   Cellular Growth vs Repair
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   Time-Restricted Feeding
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   Fasting and Glucose
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4. Nutrient Utilization: Exercise in a fasted state might limit glycogen replenishment and overall nutrient utilization necessary for muscle repair and growth. This could be a concern for those aiming for hypertrophy or intense resistance training 4.

5. Fatigue and Hypoglycemia: Acute fatigue and hypoglycemic episodes can occur, particularly if the fasting period is extended too long or if there isn’t adequate glycogen stored from prior meals. This can lead to lightheadedness, dizziness, or even serious health issues for some individuals 5.

6. Feeding and Fueling Timing: For many, balancing when to eat and train is critical. Skipping meals or eating too close to training can lead to suboptimal workouts or digestive discomfort 6.

In summary, while fasting before exercise may offer benefits like increased fat oxidation, it also presents several potential drawbacks. These range from impaired performance and higher stress levels to cognitive impacts and risks of fatigue or hypoglycemia. Individual tolerance and goals should guide whether fasted exercise is appropriate.