While there is a lot of contradictory research, as there is with most health information, there are some studies that support this protocol.

"We conclude that aerobic exercise performed in the fasted state induces higher fat oxidation than exercise performed in the fed state."

https://pubmed.ncbi.nlm.nih.gov/27609363/

"The effect of coffee, decaffeinated coffee and a control beverage on plasma FFA [free fatty acids] was studied in a group of normal human subjects.... Significant elevations in FFA were observed after coffee and caffeine which usually reached their peak in 3 or 4 hours. The administration of sucrose significantly reduced the immediate FFA response."

https://www.sciencedirect.com/science/article/abs/pii/0026049568900541

"This study for the first time shows that fasted training is more potent than fed training to facilitate adaptations in muscle and to improve whole‐body glucose tolerance and insulin sensitivity during hyper‐caloric fat‐rich diet."

https://physoc.onlinelibrary.wiley.com/doi/full/10.1113/jphysiol.2010.196493

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