I absolutely detest counting calories (same goes for counting carbs, so no keto for me). I find it a lot easier to make simple home made meals that are healthy (reduced carb, lots of protein and veggies and some fat). Then I eat slowly till I feel pleasantly full so I don’t overeat.
I have watched a lot of Fung’s videos on youtube and he does say that you still need to watch the amounts you eat since you need to consume less energy than you burn. Fasting won’t work for weight loss if you eat too much in your eating window.
I finished it last night. My understanding is that counting calories is advised against as calorie restriction itself is not the goal and this alone does not work. However in the final chapter (or Appendix B, I read them together) he points out that even feasting over the usual daily calories for the meal breaking the fast, there is a calorie deficit over the two days (for alternate day fasting) and this is a good thing, as it is essentially a dual benefit.
He does emphasise repeatedly that reduced calories generally = reduced metabolism so I was not fixating on that. Also his five steps (+fasting) focus on eating the right things, not a reduced quantity.
Ultimately do what works for you, I lose motivation quickly when focussing on calories (I have done IF successfully before but put on a lot of baby weight in the last year and couldn’t fast!) but if you’d rather have the data then go for it, just make sure to follow the fasting and type of food aims as your primary goal. The calorie reduction will then likely follow naturally as a result of IF in any case.
CICO is “controversial” because so many people want to believe they can consume more calories, i.e., food energy, than their body’s daily energy expenditure needs and magically lose or not gain weight.
CICO does still matter, but with IF your “calories in” will include the fat stores that your body was previously unable to efficiently tap due to high insulin levels. If you compress your eating into two high satiety meals during a shorter time period during the day, then hopefully you will have consumed less calories than your body’s requirements (especially when adding some moderate exercise) and the remaining balance of “calories in” will come from your fat stores.
Even a 72-hour fast is a balanced CICO: you have a caloric output that you need to meet, but you aren’t eating any calories during this time (temporary 100% calorie restriction diet), but that is OK since your body is efficiently pulling the calories in from fat stores.
I recommend watching this talk on how food becomes addictive, as managing this factor may naturally help you reduce “calories in” without it being a struggle: https://youtu.be/kN83jppeI7Q