Nutritional science indicates that fasting for extended periods leads to starvation, dehydration, and eventual death.
I suspect that even most people who are not nutritional scientists would be in generally broad agreement with the above conclusion.
Mr. Wiley Brooks appears to recognise that new practitioners will need some kind of transitional period, from his website:
Brooks explains that the "Double Quarter-Pounder with Cheese" meal from McDonald's possesses a special "base frequency" and that he thus recommends it as occasional food for beginning breatharians.
You may contact him on his fifth-dimensional telephone to ask about it.
Valeria Lukyanova, the self-styled Ukrainian Barbie doll, is trying to take it up.