Hi folks. I was looking for information as to where the body gets energy during a fast in a fat adapted individual. Assuming that this person is also weight lifting and expends more energy than the body can liberate from fat stores alone.
From what I read there is a limit as to how much of ones body fat can be converted to energy per day - (290±25) kJ/kg day or (31.5053±2.72) kCal/lb day:
So assuming based on the formula above, that for a person that has 63.5 lbs of body fat that 2,000 Calories of energy can be used for fuel. But what if this same person needs 3,000 Calories a day due to activity/exercise? Where does the delta come from?
Autophagy? - I would hope that this would be the case, but I can’t see the human body being able to quickly figure out where to find 250g (1000 Calories / 4 Calories per gram of protein) of old protein to destroy a day to continue to fuel demand. I hope that I’m wrong.
Glycogen? - I would have thought that’s near depleted since starting keto. I figured that the first 10+ lbs or so of weight loss when starting keto was glycogen and water. So I wouldn’t suspect that this would be a large source of energy to fill that delta.
Burning muscle? - I hope this isn’t the case, but I don’t know what other sources of energy are left. If one is fasting and lifting weights, Dr Jason Fung says that HGH is secreted and it’s muscle sparing. But I would suspect that would only apply to the parts of the body that where exercised during the fast leaving other parts ‘fair game’ since they where no being used.