Holmes,
Looking at your "what we know for sure" list:
1) There is an elderly man who was able to go without food and water for 10 days
2) he claims this ability was granted by a goddess, and
3) he claims he has not eaten in 40 years.
I'd change number 1 to:
1. According to the doctors in the hospital, there is an elderly man who was able to go without food and water for 10 days.
Often scientists are the worst people in the world to detect fraudulent claims of the supernatural as they tend to be too trusting. It sometimes takes a professional conman to detect where any chicanery is taking place (e.g was he allowed visitors during the period? Could they have slipped him something?). I'd like to have seen James Randi there to cast his eye over the conditions of the experiment.
The most we can say is that the doctor's are baffled.
Its also pretty weird that the guy lost some weight over the ten days - that just doesn't add up to me. As you say, what difference does a week of not consuming make over an entire lifetime of not consuming?
As for demon possession, I once heard this story about a guy some time ago who was crucified, pronounced dead and came to life three days later. He also claimed to hear voices from God. Seems like a surefire case of demonic possession to me.
PE