Fasting has never been a tradition in my family. I tried it few times in order to see how it affects chronic inflammation. My longest attempt was for 5 days, already with the pouch. Well, inflammation did not subside, I had fluid BM but not much less, and after eating again things were all the same pretty soon. But it was an interesting experience.
I found it important to have mainly warm drinks, so I wouldn't lose too much energy. In fact fasting was easier for me than sticking to a certain kind of limited diet, because I simply didn't have to think about eating.
I you are worried about weight or nutrients you might consider soup fasting or some kind of intermittent fasting.