Pardon my ignorance, but how does the research account for the benefits of caloric reduction? How do we know if it's the disciplined fasting, or if simple caloric reduction is part of the equation?

That information would help me decide whether I have to be strict about no eating. Much of the advice I've seen amounts to allowing some leeway in small caloric inputs.

While BCAAs do break your fast, that's not entirely true. For example, green tea, black coffee, ACV, and likely others do not break your fast.

This is a pretty hardline approach.

Most people allow for coffee and tea without sugar or cream.

If there are no calories you're not breaking a fast in my opinion.

BCAA's do have calories so I would say they would break a fast though.