depends on your medical issues.
For me fasting is a bad idea as I am hypoglycemic so my blood sugar would drop. I get shacky if when I get hungry and have not eatten. Plus my mood goes pretty far south. Much more than normal people.
I personally will not take parts in fast and I point to that reason of my hypoglycemay and my friends would accept that as my answer for not taking part in it. I would support them when they would do it by not eating around them or talking about food.