For Keto:
According to this timeline A metabolic switch occurs after ruffly 48 hours. I'm sure this varies on how healthy a person's health is and also their last meals..
It appears that as soon as you eat something that turns to sugar your system will go into glucose burning mode and fat will be spared. Although some eat a keto diet after fasting to stay in ketosis, but I contend anything you eat will turn to glucose.. Fasting is the most efficient, but once you break it, you'll have to start the cycle over again and it can take some time to get back into fat burning mode.
According to this timeline, after approximately 72 hours, the ketone index will hit near a maximum or what's stated as the 'therapeutic zone'. Fat burning mode occurs after glucose is depleated... Glucose appears to dramatically drop after ruffly 24 hours and seems to tip into a strong bottoming pattern after ruffly less than 48 hours.
