Fasted Workouts: Hype or Helpful?
Have you ever rushed out the door for a workout on an empty stomach? Maybe you’re just not hungry in the morning before your run, or grabbing a pre-workout snack isn’t top of mind? Believe you’ll burn more fat if you don’t eat before working out?
If so, whether intentional or not, you’re exercising in a fasted state, which is usually six to eight hours after your last meal.
Understanding how the body responds to a fasted vs fed workout can help you decide what’s best for your goals and recognize that not eating before a workout doesn’t inherently result in greater fat loss and can limit your progress.
When you exercise, your body is using a mix of fats and carbs for energy, with the balance shifting based on intensity and duration. Carbs fuel higher-intensity activity (HIIT, cycling, weightlifting, sprinting) while fats support lower-intensity, steady state movement (gentle yoga, casual walk). During a fasted workout, your body relies on fat stores for energy. This temporary dependence on your body’s fat storage does not translate to fat or weight loss unless you’re consuming fewer calories than you burn throughout the day.
What does the research say?
Resistance training done in fasted and fed states have similar effects on body composition. (systematic review)
Performing in a fasted state did not influence weight loss or changes in lean and fat mass. (systematic review)
Fasted and non-fasted groups did 1 hour of steady state cardio 3 days/week - Both groups showed weight and fat mass loss with no difference between the groups.
Short-term low volume HIIT in overweight and obese women - Fed and fasted state showed improvements in body composition but found no difference between the groups.
While research shows both fasted and fed workouts can lead to results, fueling your body before exercise can impact your energy, performance, and recovery in ways that the scale cannot measure. Additionally, fasted training tends to present itself as overall under fueling which can make recovery harder and result in the loss of lean mass.
If you need to skip your pre-workout snack, here are two important considerations:
Hypoglycemia (low blood sugar levels) can cause dizziness, weakness and even fainting. Keep a fast digesting carb source on hand such as a rice cake, apple, or candy.
Have a proper post-workout meal within 30 mins to an hour after exercise. This is a shorter window than if eating beforehand to prevent muscle breakdown.
At the end of the day, fasted workouts aren’t a secret weapon to fat loss and could hold you back during your fitness journey. Burning more fat during a session doesn’t mean you’ll lose more weight, and training without proper overall nutrition can make workouts feel harder while slowing down recovery and muscle growth. It’s important to always listen to your body and fuel it for the hard work you put in!