Appropriate article since I just completed a fast of 19hrs. No water and no food. Muslims do this every year. Last year, on average our fast was just over 18hrs. We fast each day from sunrise to sunset for 30days. Of course, we as a group of people have been doing it for over a thousand years. Cant say we started it due to science, but cant say we noticed the lack of aging either. ;)
I have never met a Muslim that didn't put on 5 kilos during ramadan from ridiculous iftars and judicious day light napping. I suspect that may cancel out any benefit fasting might have.
Personally though, it went fine in terms of productivity and energy. Trying to work out without that nap was pretty brutal but fasts are long enough to fit it in after work.