Where people most commonly come unstuck with fasting is when they refeed.
"Every fool can fast, but only the wise man knows how to break a fast."
-George Bernard Shaw
We believe what you eat after you fast is critical to achieving any long term benefit from your sacrifice during your fasting. Unfortunately, many fasting proponents, with their fear of the short term insulin response to food actually cause their followers to consume low satiety, energy-dense nutrient-poor foods that leave them in a constant binge/restrict cycle.
Sadly, they continue to lose and regain the same few pounds without achieving the meaningful, long term results they hoped for, in spite of their deprivation and sacrifice.