So, I asked the nutritionist today whether I should be shooting for 600-800 gross calories (total eaten, period) or net calories (total eaten minus calories burned in exercise). The answer?

Net calories. She said that it's ridiculous to believe that a 6'1 man can live on 800 calories a day if he's burning 400 in exercise. That's effectively asking my body to live on 400 calories a day; no wonder I was feeling woozy and nauseous and not well.

Now that I'm eating about 1000 calories per day (and burning 200-300 on average), I'm feeling much, much better (and still losing about a pound a day!)

So good to have definitive answers to these things

That was a really smart question to ask! I don't know if I would have thought to ask that. Thanks for the info.