You'd be amazed at how much your metabolism can slow down when you fast. When in college I saw a presentation at the medical school where they showed the effect of low calorie diets.

It's not unusual for people on low calorie diets to see a 30-40% drop in their basal metabolic rates. And those are diet where the person is getting some food.

I agree that 980 kcal/day is pretty low, especially for someone of his size, but it's not completely out of the question.

It will apparently also go the other direction, speeding up to consume excess calories in order to maintain your "normal" weight - http://www.youtube.com/watch?v=MHQshbJATVQ - skip to about 49 minutes. One of the guys in this experiment, where they doubled their caloric intake for about 6 weeks, had his metabolic rate go up 30% to compensate.

> Once you make fat cells, they never ever go away.

Well, that's pretty depressing. Maybe the next big thing in combating obesity would be finding some mechanism to get rid of extra fat cells?

Seems like you can make them look for fat and burn it. Google "brown fat". It seems that cold exposure activates this mechanism.

I think the fat cells in your body have a ratio skewed much more towards fat, and are an exception to the "your body is 2/3rds water" rule-of-thumb.

I suspect this is the answer.

Also note that he was consuming nutritional yeast & vitamins which may have offset a small part of his energy use.