I am newer to the forum but hope your fine with me responding.
As far as what constitutes a fast. Most people agree whatever you consider a fast is one. You can do a fast that is water only, which usually also allows coffee and tea. A lot of people add broth into extended fasts. Some people do a fat fast, where they eat no carbs or protein and try to keep insulin down. Some people have BPC on a fast because it helps them not be as hungry.
Which fast you do depends on what you want from it.
If you are looking for a health benefit like autophagy I believe you need to do a water fast, as calories limit autophagy. Im not sure how calorie restricted your fast has to be @brenda might be more helpful here as she does more fasts and is joining the Intensive Dietary Management Program with Dr. Fung.
Speaking of, a lot of the information I am sharing on Fasting can be found in The complete guide to Fasting which is a book from Dr. Fung
As far as tips and tricks from my experience.
Don’t start with a Giant Fast. It is much easier to do several smaller fasts working your way up to a five day fast.
If you begin to feel bad STOP. If you get hungry you should eat. if you are light headed you should eat. if you get a headache you should eat.
Day two is the hardest. If I get any notes of hunger from my brain they come on day two for me. after day two I don’t even really notice I am not eating.
Make sure you are getting salt.
Breaking a fast is important. You shouldn’t just go back into eating normally. and most people overeat when they begin eating again. You should slowly reintroduce food. start with a handful of nuts, in a couple hours have a couple eggs. then have a regular meal later.
I may have missed some things, and I am willing to answer more questions if you have them. Also feel free to check out the Fasting Section for some more information and personal stories.