Should you eat before exercising? Long story short, it depends on your goals and the type of exercising you plan on doing. If your goal is to burn the most amount of fat during exercise then yes, create a program that incorporates fasted, low intensity cardio. However, if your goal is performance or you plan on doing higher intensity exercises like CrossFit, then the science says it’s better to have a balanced meal with an emphasis on carbohydrates a few hours before training (PMID 27609363).
ATP, or more affectionately known as Adenosine Triphosphate, is a molecule within the body that provides cells in the body with energy through the conversion of protein, fats, and carbohydrates. Which macro is used during this conversion depends largely on the type and duration of exercise and energy expenditure. From an energy standpoint, the human body is broken up into 3 different systems:
The Phosphagen System- The energy system typically used during the first 10 seconds of an extreme exercise (short sprints) or for exercises like weightlifting. Typically considered an anaerobic system because the oxygen requirement for energy conversion is limited, this energy system uses primarily carbs and fat.
The Glycolytic System- This is the energy system used primarily during higher intensity workouts like CrossFit or longer, higher intensity running/swimming/biking. This energy system uses primarily carbs and oxygen for its fuel.
The Oxidative System- This is the primary system used during long duration, low intensity type exercises (like long walks, or low steady state cardio). The primary source of fuel for this energy system is fat.
While all forms of exercise burn calories, the best bang for your buck if you want to focus purely on fat burning would be to incorporate in some fasted, low intensity cardio into your routine. According to PMID 27609363, performing low to moderate intensity aerobic exercise in a fasted state induces a significant increase in fat oxidation during exercise (Cambridge University, 2016).
However, if your goal is more performance oriented or your workout regimen consists of more higher intensity/weightlifting type of exercises, a small meal with some carbs and fat might be more beneficial to your overall goals. Speaking from personal experience, there is very little that’s worse than hitting a wall halfway through a CrossFit mashup.
No matter the exercise, it’s important to have a plan and incorporate the right forms of preparation into that plan. If you’re goal is burning fat, try some fasted cardio first thing in the morning. If your goal is to get stronger or fitter through lifting and higher intensity programs, then fuel your body with some carbs and fats about an hour before your session.
Cambridge University (2016). Retrieved from https://www.cambridge.org/core/journals/british-journal-of-nutrition/article/effects-of-aerobic-exercise-performed-in-fasted-v-fed-state-on-fat-and-carbohydrate-metabolism-in-adults-a-systematic-review-and-metaanalysis/0EA2328A0FF91703C95FD39A38716811