It's not even that tough. My whole youth group would do it with no complaints. I remember doing liquid fasting as a teen for days to raise money for starving people. We would get sponsors based on the length of our fasting with a maximum time period and supervision on  safely breaking the fast together. It was meant to help others and breed compassion and empathy in ourselves. Pretty easy when you tell yourself that every hour of discomfort can feed dozens for days. Based on the size of Christians I see today, my guess is that churches today don't do this.