Congratulations on all your success. Unfortunately it isn’t surprising that a doc will not accept the truth of your experience vs. the (inadequate) training they have received or random content they have read.
He doesn’t properly understand the hormonal metabolic system in all its complexity hence his over-simplistic view of fat metabolism. You take in high levels of fat for several reasons…
- speed and efficiency of fat adaptation
- provision of sufficient energy to enable healing, etc.
- maintenance or raising of BMR through getting the body used to higher energy availability
- etc. (can’t remember others ones)
The key point is that the body is generally a better decision maker on how it processes inputs to its system than the brain could ever be. Insulin resistance (and resistance or sensitivity to other hormones) of various organs determines our reactions to inputs but this is difficult to understand, harder to measure and even harder to predict. The big trump to all of this is brute forcing things through calorie restriction which works because the body will put everything else on hold to adjust to an energy deficit until it has created a new homeostasis (usually at an unpleasantly low BMR). Docs think that because CR “works” it must be good and the best lever to pull and it is hard to get them to think otherwise since that would involve independent thinking… the very antithesis of modern medicine which is based on unthinking compliance to the “standards of care”.
From a purely definitional standpoint… lipolysis is the burning of fat, one of the products of which are ketones (and fatty acids), both of which are burned as fuels instead of glucose in many organs/parts of the body. The body fat vs. dietary fat burning question is far too murky to get a good answer. I have experienced high appetite, low appetite, weight loss, stalls and gains on exactly the same inputs suggesting that the missing X factor is the body’s metabolic evolution over time. At different times the body has been happy to use body fat, other times not, sometimes it uses body fat but replaces lipids with water in the adipose cells so the scale doesn’t show the change until way later, making it hard to tell when and why you burned the fat. It is so damn complicated and unproven, it is a fools errand to try to convince an MD who isn’t ready to be convinced. I would tell him/her to read what more enlightened MDs e.g. Fung, Unwin, Berry, etc. are saying and let him/her make their own minds up. In the meantime, do what you believe in since you probably know more than your doc.