If you start out weighing ~450 pounds, the math on living without eating is pretty straightforward. The person in question did a medically supervised fast. He consumed water, a multivitamin and a small amount of yeast. (Also potassium tablets for a few months) His weight went from 456 to 180 pounds over the period of the fast; he regained about 15 pounds in the following 5 years.

He apparently defecated every 40-50 days.

(Though the stories about this are pretty recent, the event being described happened in 1965.)

http://www.abc.net.au/science/articles/2012/07/24/3549931.ht...