I love the Book, just read it.
This was in his website - blog.

"Dr Fung, in regards to your comment “If you try to keep a constant diet, the body will adapt to it”, does this not apply to consistent IF? If I do 24h fasting every day (eating only dinner) wouldnt the body adapt to that type of dieting too after a while? Also, I am doing 2-3 24hr fasts per week and the weight is very slowly going down (I only have 3-4kg to loose, i’m helathy and not overweight and not on any meds) , is it dangerous to do 24h fasts every day until I reach my weight goal (and then go down to 1-2 times a week)? Or will it stress my body trying to get results too quickly (and being on constant calorie deficit as I dont eat more than 1000kcal when breaking my 24hr fasts)? Thanks!

Dr.Jason Fung: We often find, in our clinic, that daily 24 hour fasting is less effective than occasional longer fasts.

Kind of makes me think it is a waste of time to do less than 24 hour fast.