Indian doctors are studying a remarkable 83-year-old holy man who claims to have spent the last seven decades without food and water.

Military medics hope the experiments on Prahlad Jani can help soldiers develop their survival strategies.

The long-haired and bearded yogi is under 24-hour observation by a team of 30 doctors during three weeks of tests at a hospital in the western city of Ahmedabad.

Two cameras have been set up in his room, while a mobile camera films him when he goes outside, guaranteeing round-the-clock observation.

His body will be scanned and his brain and heart activity measured with electrodes.

"The observation from this study may throw light on human survival without food and water," said Dr G. Ilavazahagan, who is directing the research.

"This may help in working out strategies for survival during natural calamities, extreme stressful conditions and extra-terrestrial explorations like future missions to the Moon and Mars by the human race."

Since the experiment began on April 22, Jani has neither eaten nor drunk and has not been to the toilet.

"The exercise of taking this yogi under the medical scanner is to understand what energy supports his existence," Dr Ilavazahagan added.

"Jani says he meditates to get energy. Our soldiers will not be able to meditate, but we would still like to find out more about the man and his body."

Jani, who dresses in red and wears a nose ring, grew up in Charod village in the Mehsana district in Gujarat.

He claims to have been blessed by a goddess when he was aged eight, which has enabled him to survive without sustenance.