My point was that muscle protein catabolism isn't simply stopped at a certain calorie number. Yes, it is spared (less used) with adaptation to less food, to a certain point. That point will depend on the individual.

Any food is better than no food, as long as you have water also, as Doug's nutrition page states. A rough estimate for a person to maintain their body weight at rest is (body weight x 10 = calories/day needed to maintain body weight at rest). With physical exertion that number goes up. If you lose some weight, so what. Most of us need to anyway.