Probablem with those is low bulk when they get in your belly, even though they swell. When you are hungry, your body wants to feel full, and they can't warm you up like a hot meal can.

Food plays a much greater role in morale than most people think- that's what gets Les Stroud, his body is doing all kinds of funny things to conserve energy before it starts to autocannibalise. I'd bet (a little) money that he's mostly fine in terms of caloric consumption when he's gone three days without so much as a cricket. Instead, I wouldn't be at all suprised if it's neurochemistry messing with him. Tired, feeling a bit blue, we've probably all seen him hit that point around the third or fourth day. That isn't so much starvation as it is depression. They've known for decades that below a certain caloric consumption, you emotions and ability to think start to shut down, but if you still have sufficent reserves on your body and you get some food in you, you are good to go. (Thank you Herr Mengelev (sp), may he rest in torment.)

I know from my experinces that holds true, at least for me.