There are benefits and disadvantages to exercise while fasting. If you are trying to lose weight or body fat, it might help you achieve your goal. However, if your goal is to improve athletic performance, it may hinder your progress.
Fasted Exercise for Weight Loss
If you are exercising to lose weight, doing so while fasting can be beneficial. A 2016 study in the Journal of Nutrition and Metabolism showed that exercising while fasting increases fat oxidation. Similar findings were published the same year in the Journal of Translational Medicine. The study worked specifically with athletes, who fasted for 16 hours and completed resistance training before their first meal at 1:00PM. Researchers found that body fat decreased while muscle mass was maintained.
There's a reason why these results came about. They're based on the way your body creates energy. When food is available, your body uses what you consume. Just like a car needs gas, your body needs food for fuel. Once all the food in your system has been digested, your body seeks another source of fuel. That's when it begins to tap into your fat stores.
Exercising while fasting can also reduce hunger levels, as shown in a 2013 study. After fasted exercise, meals are more filling and satisfying, which ultimately leads to better weight management.
Fed Exercise for Performance
On the other side of the coin, if you don't have a weight loss goal, there's no need to exercise while fasting. Food fuels performance, so if you're looking to improve your strength and endurance, it may be best to focus on eating items that will give you the energy you need for your workouts.
A recent study in the Scandinavian Journal of Medicine and Science In Sports compared a group of participants who fasted during exercise to a group that ate prior to their workout. They confirmed what previous studies found, which is that fasted exercise results in desired changes in body composition. They also concluded that eating before exercise is the ideal choice for aerobic performance and overall endurance. Participants who were fed before workouts were able to progress their training while those who fasted regressed.
This result is particularly significant for athletes when practiced over time, as indicated in a study that focused on Muslim Judo competitors fasting and training during Ramadan. The study found that for the first few days, performance was unchanged, but as the month continued, performance slowly decreased.
Precautions for Working Out While Fasting
While there aren't any specific rules about how long you should exercise while fasting, it's important to listen to your body. If you choose to exercise while fasting, take measures that will keep you safe and healthy.
- Make sure that you are properly hydrated. Drinking water aides in blood circulation, keeps your energy high, and prevents heat exhaustion.
- Monitor your energy levels. You may feel slightly fatigued during your workout. This is completely normal while fasting. If this happens, slow down. Choose lighter weights, lower your tempo, and take more breaks. If you start feeling dizzy, stop exercising.
- Rest. You may need more recovery time than normal while fasting. You can either cut your workouts down so that they are shorter or rest a full day between each session.
- Focus on form over speed. Since your endurance may be impaired, focus on maintaining proper form and alignment instead of pushing yourself to work at a high intensity. This will prevent you from unintentionally injuring yourself as fatigue sets in.
Test the Waters
Exercising while fasting can be a great tool for weight and body fat loss, but not for performance-based fitness. If you do have a weight loss goal, try it out. Just be sure to ease into it slowly and take precautions that will keep you safe and injury free. Start with one to three days of fasted workouts and see how your body reacts. Work your way up from there.