Does ____ break a fast?
That might be the most common question I've seen from people new to fasting.
From my point of view, the answer comes down to two things:
1. What are your goals?
2. What's in the food (or drink, etc) you want to use?
First, why are you fasting? What do you hope to accomplish?
Maybe you want to lower your blood sugar, reduce your risk of diabetes, reduce your body fat, or improve your mental clarity.
Or something else.
Whatever your goals are, instead of asking whether something will "break" your fast, ask whether it will prevent you from reaching your goal(s).
Second, what's in the food (or drink, etc.)?
If you're thinking about eating or drinking something while you fast (i.e. a sort of "dirty" fasting), it helps to know exactly what's in it.
How many grams of carbohydrates, protein, and fat does it have? How many calories?
It also helps to know what carbs, protein, etc do inside the body. Then you can relate that back to your goals.
Obviously this isn't comprehensive, but in general:
-- avoid carbs as much as possible, because they raise your blood sugar and insulin, and promote fat storage
-- protein is kind of okay, but may limit some more "advanced" benefits from fasting (like maximal autophagy)
-- dietary fat (like mct or coconut oil) is the best thing to supplement with, but doing so can reduce how much of your own body fat you burn in the short term
I also wrote a longer article on this topic recently, going into more detail and covering a lot of specific examples that people ask about a lot. I'd love to hear any feedback if anyone cares to share. :)
https://fastingwell.com/what-breaks-fast/
Answer
Was just searching on this topic, so very timely. I am particularly interested in proper supplementation of electrolytes whilst fasting, and in particular potassium and magnesium, and whether they have any impact on autophagy. But as you pointed out it is a big topic where little work has been done.
I enjoyed your last thought - that it is better to have fasted with supplements than to not have fasted at all. All too often we get caught up in the science of it and diminish our efforts. But what better time to be proud of ourselves!