It's a question worthy of discussion.

I like to think that my extended bachelorhood was the best training for this: famine and low quality food plus extensive physical exercise for days; counterbalanced by a bacchanal, a mass of steaks or pork chops on the barby, washed down with quantities of beer, fresh whole-grain bread, and uncooked veggies. This is the purest hunter-gatherer diet IMO.

If I tried that now, it would probably kill me. Eventually.

But to respond to the OP: I think I would try to put on the 10+ pounds, but without radically sacrificing cardio fitness and core strength. For me, that takes some work: the only way I can add a lot of weight is through cheap, lazy calories (specifically, sweet and complex dark ales). Broadly speaking, though: regardless of the situation, nobody can steal those calories from you; that's why we have the capability.

A (mostly) healthy body will respond and adjust to conditions. I had a practical test of this last year -- 60 hours with nothing but clear fluids in preparation for a medical test. I thought it would be a lot harder than it was. Did I miss food? Yeah, but I wasn't starving by any stretch. Mostly I was grossed out by the limited diet, but I needed the fluids and salts. But I was able to keep working (with the exception of highly creative problem solving), I was able to drive, etc. etc. And after 48 hours the food craving kind of stopped; it was there, but in the background, and I could ignore it. After the tests, I walked around a bit and realized I could have kept functioning quite a while longer. Nice to know.

Long-winded answer. Sorry.