So I saw Chai's last post on the way to the gym, and it buzzed around in my head in the background as I watched the Mets hammer the Yankees, and I formulated a response, and get back here and it's already covered...
Basically, what I was gonna get at is that, first, flushd's example already pretty much covered the 10,000 calorie thing ("keep eating 10,000 calories a day until the baby is born, just make it good food"). One would assume from the "health nut" part that she wasn't taking in anywhere near 10,000 calories a day, yet she still gained weight rather than losing it (though not much, and she lost weight later on).
The other part is what's been covered about it not being necessary to take in nearly that many calories to stay really fat. Most people (I'd say all, but who knows) don't enjoy being fat, and have repeatedly attempted to lose weight, often by dieting. Our bodies react to starvation (taking in few enough calories that weight is lost) by holding on to those fat cells ever-more tightly. It becomes harder and harder to lose weight (and KEEP it off) every time someone goes on one of those diets.
So a person who's been doing that for a long time can just eat a plain ol' regular diet and still not be able to lose weight.
That's not going into metabolic disorders, etc., etc. Person A and person B can eat the exact same thing and get the exact same amount of exercise and still wind up at completely different weights because of biological factors.
IF a person was really taking in 10,000 calories a day, that'd probably be something pathological, and something as simple as a doc telling them to stop probably wouldn't have any effect.
In sum, I think (but don't know! any OB-GYNs here?) that a doc would say "eat as healthily as you can, get enough exercise, but don't
try to lose weight right now."