A Breatharian is one who follows a Dieting in which no food (and possibly no water) is consumed. Breatharians claim that they are sustained by 'light energy' (or prana) alone, and that this 'diet' is an option for anybody, once the proper techniques for accessing it are made known.
Both current scientific theories about nutrition and generally accepted common sense indicate that a person who followed these diets would die of starvation or dehydration.
Indeed, there is no accepted scientific evidence for any of the claims put forward by the breatharians. The only breatharian to undergo scrutiny -- Ellen Greve (aka Jasmuheen), on Australia's 60 Minutes http://sixtyminutes.ninemsn.com.au/60/stories/1999_10_24/story_57.asp http://www.ratbags.com/rsoles/comment/jasmuheen.htm -- became ill and bowed out after a few days without food or water, citing Stress (medicine) and pollution as the cause for her symptoms.
The well-publicized deaths of Verity Linn and Lani Marcia Roslyn Morris whilst attempting to enter the breatharian "diet" have drawn further criticism of the movement. To date, three deaths have been linked to breatharianism. http://news.bbc.co.uk/1/hi/scotland/453661.stm http://www.rickross.com/reference/breat/breat08.html
The breatharian movement also suffered a credibility blow some years ago when another of its leading lights, Wiley Brooks, was caught sneaking into a hotel and ordering a chicken pie.
However, Paramahansa Yogananda's Autobiography of a Yogi details two alleged historical examples of breatharianism, Giri Bala and Teresa Neumann.