I'm almost 100% sure those 14 subjects were muslims fasting during ramadan. Which happen to be:
- 4 weeks in length
- from Dawn to sunset
- No food or drinks including water
- Easier to control group, as you cant monitor 14 people through 4 weeks and make sure they don't cheat. So the cheating is kept to the minimum because of the religious reasons.
I also assume, that those are men only. Women are not allowed to fast when on their period which happens to be once a month.