This question is about Running
Studies have shown that a fasted morning run may increase the utilization of fat as a fuel source, improve skeletal muscle function, enhance metabolism, and reduce appetite [ 1 2
1]. Exercising in the fasted state may also reduce intake of food throughout the day, which can translate to weight loss [
2]. However, running in a fasted state may impair performance if you're doing maximal or near-maximal efforts since glycogen stores decrease overnight. In this case, eating something small before a morning run can be beneficial.
Wallis, G. A., & Gonzalez, J. T. (2019). Is exercise best served on an empty stomach?. The Proceedings of the Nutrition Society, 78(1), 110–117. https://doi.org/10.1017/S0029665118002574
Bachman, J. L., Deitrick, R. W., & Hillman, A. R. (2016). Exercising in the Fasted State Reduced 24-Hour Energy Intake in Active Male Adults. Journal of nutrition and metabolism, 2016, 1984198. https://doi.org/10.1155/2016/1984198
McCall, P. (2015). Does Fasted Cardio Provide Significant Benefits? ACE Fitness. Retrieved from https://www.acefitness.org/education-and-resources/professional/expert-articles/5696/does-fasted-cardio-provide-significant-benefits/