An 83-year-old Indian holy man who says he has spent seven decades without food or water has astounded a team of military doctors who studied him during a two-week observation period.

Prahlad Jani spent a fortnight in a hospital in the western India state of Gujarat under constant surveillance from a team of 30 medics equipped with cameras and closed circuit television.

Prahlad Jani ... confounded doctors who don't understand how he survives. Credit:AFP

During the period, he neither ate nor drank and did not go to the toilet.

"We still do not know how he survives," neurologist Sudhir Shah told reporters after the end of the experiment.