Think this sums it up
"The human body is constantly shedding energy: mechanical energy is transferred to the surroundings by the muscles, and even when perfectly still, heat energy is being conducted to the surrounding air. The laws of thermodynamics imply that this process cannot continue indefinitely without the lost energy being replaced. The extraction of energy from lipids, saccharides, and proteins in the animal body is fairly well understood, and no other supply has been found which could possibly supply the energy required for the continuation of life. Anatomically, the only route by which these chemicals can be delivered to the respiratory processes is through absorption into the blood. There are no known reagents contained in air alone that could possibly deliver the kind of energy required for the sustenance of life. There is no photosynthetic process known to occur in the human body, nor could any conceivable such process supply energy to the body at the required rate, given the surface area and reflectivity of the human body. Tragically, there is ample evidence in history and the current time of the known effects of starvation and dehydration.
To explain their claimed ability, Breatharians explain that the energy for life is supplied by mystical or supernatural forces, such as Prana. Breatharian.info offers this explanation “for the scientifically minded”:
One explanation, purely scientific, which comes from a nuclear physic[sic] says as follows: the organism consists of tissues, which are built of chemical molecules, and next these molecules are built of atoms. Atoms consist of electrons and protons, which are built of smaller elements. As the result of this way of looking for an origin element, we reach the point, where the matter does not exist. There, we have only something, which we can call vibrational whirls of energy. […] All the matter which exists in the Universe, including the human body, is comprised of whirls of vibrational energy. […] There are centers in the brain, which manage body energy and chemistry […]. In this way, the organism lives and builds itself using these whirls of energy.
Skeptics will note that this explanation is pure Pseudoscience; it uses scientific terms such as energy in non-precise ways, and contradicts known facts discovered by science. Particularly, it does not address the problem of the continued loss of energy from the body. "
Seems like a dangerous practice to me...