There are many Hindu priests who can do this. I have tried it on multiple occassions, but just as fasting i.e. not eating at all, not over drinking and not 'living off the air/light', for periods of upto 6 days and as Ama-Gi said; I also felt normal if not stronger. I felt I could have continued but would get tempted by chocolate or something or couldn't be bothered to continue
. Once the initial hunger pains subsided in the first day or day and a half it was fine. Hence those with proper training and knowledge in breathing in nourishment can do it for much longer and there are stunning examples that I have known others to complete in religious/spiritual devotion.