Exercising on an Empty Stomach and Fat Loss

Young woman sitting in the gym with a bottle of juice and other person behind her
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This is a popular theory based on the idea that your blood sugar levels are low when you've gone all night without eating which, supposedly, targets more fat burning during exercise. But does working out when you're hungry help you burn more fat?

Not necessarily. The problem is that just because you're using more fat as fuel doesn't mean you're actually burning more fat off your body. Burning fat is more about overall calorie expenditure, not just about the type of energy your body is using for your workout.

Fasted Workouts

A 2019 study reports that aerobic exercise after an overnight fast increases fat utilization, improved lipid profiles, enhanced metabolism signals to skeletal muscle and adipose tissue, and overall decreased caloric intake throughout the day.

However, these studies are short-term, done mostly in young healthy men, and seems most beneficial for people at risk for cardio-metabolic disease. Although the 2019 study may seem promising, the larger body of research for continues to recommend proper fueling with carbohydrates for athletes.

At least one other study, published in the National Strength and Conditioning Journal, has shown that your calorie burn is the same during cardio whether you eat or not. In fact, the study's author Brad Schoenfeld suggests that working out in a fasted state at higher intensities may affect your protein stores, reducing it by up to 10.4%. If you're trying to build muscle, that's a big loss. Furthermore, performance will be negatively affected.

As he says: "As a general rule, if you burn more carbohydrate during a workout, you inevitably burn more fat in the post-exercise period and vice versa." Other experts advise that the 24-hour energy balance is the best determinant in reducing body fat.

Finally, if you skip your meal or snack, you may not be able to work out as long or as hard if you're hungry. That means you may end up burning fewer calories than if you'd eaten something and worked harder. Also, inadequate fueling for your performance overall can affect performance, muscle building, and weight loss goals.

Benefits of Eating Before Exercise

We each have to find a system that works for us. You may be fine doing cardio without a meal in the morning, but strength training may require more fuel to really challenge your muscles. Here are some of the benefits to eating before working out:

  • Avoid low blood sugar, which can make you feel dizzy or nauseous (this is especially dangerous for people with existing blood sugar issues such as diabetes.)
  • Boost recovery and strength gains
  • Make your workouts more enjoyable (since you're not thinking about eating the whole time)
  • Sustain longer, more intense workouts and greater performance

The best answer is to do what works for you. Don't go hungry just because you think you're burning more fat. After all, if you cut it short or lower the intensity because of low energy, how much fat are you burning anyway? The thing is, you may need to experiment before you find what works and what doesn't. Whatever plan you choose, if you're preparing for an event make sure your training is consistent with your plan for the day of the event.

If you do eat before a workout, make sure you give your body time to digest. Large meals should be consumed 4–6 hours prior to a workout. Then choose a light, simple, low-fiber, low fat snack that includes 50 grams of carbohydrate and 5 to 10 grams of protein 30 to 60 minutes before your scheduled workout.

Pre-Workout Snack Ideas

  • Apple with cheese
  • Banana or any other type of fruit
  • Energy bar or gel
  • Fruit smoothie
  • Greek yogurt with fruit
  • Oatmeal
  • Sports drink

If you just can't stomach eating anything early, just try a sip of orange juice or maybe a couple of bites of a granola bar. Even just a little energy can make a difference in your workouts.

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5 Sources
Verywell Fit uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. Kerksick, C.M., Arent, S., Schoenfeld, B.J. et al. International society of sports nutrition position stand: nutrient timingJ Int Soc Sports Nutr 14, 33 (2017). doi:10.1186/s12970-017-0189-4

  3. Schoenfeld, Brad MS, CSCS. Does Cardio After an Overnight Fast Maximize Fat Loss?. Strength & Conditioning Journal 33.1 (2011): 23-25. doi:10.1519/SSC.0b013e31820396ec

  4. Fekih S, Zguira MS, Koubaa A, Masmoudi L, Bragazzi NL, Jarraya M. Effects of motor mental imagery training on tennis service performance during the ramadan fasting: a randomized, controlled trialNutrients. 2020;12(4):1035. doi:10.3390/nu12041035

  5. Kerksick, C.M., Wilborn, C.D., Roberts, M.D. et al. ISSN exercise & sports nutrition review update: research & recommendationsJ Int Soc Sports Nutr 15, 38 (2018). doi:10.1186/s12970-018-0242-y