Should you eat or fast before you exercise?

There always seems to be a debate on whether or not you should eat before you exercise.  A lot of people swear that performing fasted cardio first thing in the morning is the best way to lose weight. The rationale behind this strategy is that if you are in a fasted state your body will burn more fat while you exercise as insulin levels are low, glycogen levels are low (stored carbohydrates used for fuel) and therefore your body is forced to utilize fat as a fuel source which would lead to greater weight loss, specifically fat loss over time.


Dr. Brad Shoenfeld and fitness rock star Alan Aragon designed a study to find out (Research Article on Fasted Cardio). For the study, they recruited 20 young recreationally active females and put them through a 1 hour steady-state aerobic exercise session 3 days per week for a 4-week period. Half the subjects completed the workout after an overnight fast while the other group consumed a meal replacement shake prior to the workout.  After 4-weeks, both groups experienced the same amount of weight and body fat loss with no differences observed between groups. Moral of the story, fasted cardio is no more effective than consuming food prior to a workout in terms of promoting fat loss over time.  Therefore, find out whatever works best for you. Personally I don't function well without a little food in me before I exercise so I recommend eating something especially if you are completing a workout done at a higher intensity as some people may feel light headed or dizzy.

If you are interested in learning more, check out this interview with Dr. Shoenfeld as he discusses the topic in more detail (Fasted Cardio Interview).