Hi
@Pipp
I have found Jason Fung's comments on fasting, low cal and dropping basal metabolic rate fascinating - and totally supported by my personal experiences.
His website holds all the info, in a series of short articles (some of which seem to be identical to pages in his book, Obesity Code).
He quotes studies done on both fasting, and on low calorie eating, and there seem to be a few things that I have gleaned you may find interesting. Intermittent fasting, longer fasting, 5:2 and similar diets don't seem to drop BSR (basal metabolic rate) even when conducted in the long run. Whereas reduced cal diet where consistent calories are eaten every day, do drop the BSR after a while weeks? months? He quotes some fascinating studies on this.
For this reason I have chosen to fast on only 3 days a week, and am making a deliberate effort to eat my normal amount of food on non-fasting days. Like you, blood glucose control is more important for me, than weight loss. And in my case, my main goal is reducing insulin resistance.
The graph he quotes (will try and find the link)
https://intensivedietarymanagement.com/obesity-solving-the-two-compartment-problem/
and accompanying references, seem to suggest that ketosis is pivotal in reaching this state of sustained BSR while fasting. The chart shows how glycogen reserves are used up, and as they fall, ketosis steps up to replace the fuel.
I remember Voleck and Phinney quote a study (in the book referenced in my sig) that glycogen reserves in the liver/large muscles vary WILDLY from person to person, and obese metabolically challenged people can carry many times the 'usual' amount of glycogen. Obviously, I am both of those things, so am assuming that I have equally large reserves that I need to get rid off before reaching ketosis. V&P go as far as to suggest that it may be necessary for some people (often middle aged women => Me, of course) to drop their carbs lower than 20g carbs a day to remain in ketosis, and prevent refilling their glycogen reserves. Joyous news, eh?
Sadly, since my body isn't reaching ketosis on 24 hr fasts, even after 2-3 years of very low carb eating, I am thinking I carry a large amount of glycogen
I still get small glycogen dumps for at least 1-2 days of fasting.
so I may have to increase the length of the fasts.
and eliminate carbs almost completely.
Otherwise it is like taking two steps forward and once step back, whereas if I could reach ketosis and stay in it, even when not fasting, I would be walking slowly forwards all the time, rather than this 2forward, 1back nonsense.
The most benefit (in terms of insulin resistance reduction and nearing ketosis) was when I fasted 24 hrs, then fat fasted 24 hrs, then fasted another 24. Best readings I have seen yet for both bg and ketones.