The post-exercise 'anabolic window' concept is based on subjects training after an overnight fast.

“So, John Ivy and Robert Portman put out this book called, 'Nutrient Timing', and they focused on this narrow post-exercise window of opportunity, they called it. So, the anabolic window. The concept was you needed to consume protein, and quickly digesting carbs. So, a fast-digesting protein, lightning fast, highly glycemic, highly insulinemic carb source, together within 30 to 60 minutes post-exercise, in order to maximize the anabolic response, maximize recovery, and then maximize your muscle gain.”