Fasted Workouts: Yes or No?

March 2, 2015


This scenario probably sounds familiar:  you wake up at the crack of dawn for a quick, high-intensity workout before starting your day and contemplate to eat or not to eat. You want to have the most productive workout possible – feel energetic, non-sluggish and ready to take on the world.  Does this require shoveling in calories pre-workout?  Or does it mean skipping the pre-workout meal entirely?  Like many other aspects of fueling for sport, the answer is individual. 


When you consume a snack or meal before tackling that training session, the body will then use the food in the gastrointestinal (GI) tract to fuel the workout.  With the absence of food in the GI tract, the body is forced to pull from its reserves – glycogen (storage carbohydrate) stores or fat stores.  Since our glycogen stores are limited to 2-3 hours worth of energy, it is advantageous for athletes to train their bodies to use fat more efficiently as fuel.  This is the concept/strategy of Metabolic Efficiency Training! 


Here are some considerations for determining whether that pending workout should be fuel-fed or not:     



  • This factor is perhaps the most important to consider.  Workouts 3 hours or less in time can be performed in a fasted state.  Your body pulls energy from your internal stores.  Fat reserves are used in lower intensity training; carbohydrate jumps into effect when intensity increases.  The goal of Metabolic Efficiency Training is to encourage fat utilization whenever possible as these stores are prevalent.  Note that fasted workout training is a progression, meaning that it must be slowly worked into over time if the body is used to a pre-workout calorie supply.  If the workout duration is over 3 hours in length, a pre-session snack or meal will be in order – something that provides the body with carb + fat + protein (i.e. plain, full-fat Greek yogurt with fruit and nuts). 


  • The intensity of your training session determines the fuel source used – carbohydrate or fat.  As intensity climbs, fat utilization plummets and carbs become key.  Metabolic Efficiency Training involves fueling and exercise strategies designed to train the body to utilize fat more effectively at higher intensities.  This being said, even a high intensity workout of 2 hours can be fueled by tapping into internal fat stores (remember the 2-3 hours worth of carbohydrate reserve in the body) rather than by placing the body in a fed state with calories.  Over time, the goal is to activate fat-burn to occur even at higher intensities, which improves endurance capacity as an athlete.  If the high-intensity workout is over 2 hours in length, a pre-session snack or meal may be in order – something that again provides the body with carb + fat + protein.


  • The decision to fuel or not before a workout can have a profound effect on the GI system for many athletes.  When there is food in the stomach, high-intensity workouts may become more challenging – creating a feeling of fullness or sickness.  For some, it is easier to complete shorter workouts fasted to avoid this feeling entirely.  This is fine!  Training the body to use internal fuel stores is beneficial.  For those athletes who need to have something in the stomach before completing any training, this is fine too.  I just recommend ensuring the pre-workout meal or snack is something Metabolically Efficient, again carb + fat + protein. 


  • Whether the task at hand is a swim, a bike or a run, the workout can absolutely determine the pre-workout fueling strategy.   Each sport requires different breathing techniques, and different intensities.  Some athletes may be fine eating right before a bike ride, but not before a swim or run.  This is where the individuality comes into play.  Performing the workout in a fasted state is actually helpful, unless the workout exceeds the 3-hour maximum timeframe, in which the athlete will could potentially run out of storage fuel.  If the workout is done in a fed state (with breakfast), the combination of nutrients becomes the most important factor.  Avoid consuming an all-carb or very heavy high-carb snack or meal and therefore keep blood sugar stable before beginning your workout.  

These considerations are each important in determining whether to complete the workout in a fasted or fed state.  Fasted workouts can be very helpful when completed in the correct way!  Seek the help of a Metabolic Efficiency Training Specialist (METS) like myself for further guidance in the area of fasted workouts.  

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