There is some debate about how much weight women should put on during pregnancy, but the debate centers on the total amount - NOT whether they should put on weight. Every study I've seen recommends women eat more calories when pregnant - this is absolutely important. In other words, women should put on weight while pregnant.
Several new studies say that being pregnant does not give women a blank check to eat as much or whatever they want. What the correct amount of calories is at the center of the debate. Every pregnant women should consult with their doctor and be as honest and forthcoming about what they are eating, how much they are eating, and what they can and cannot keep down if they have morning sickness.
What you are describing, however, does not appear to be morning sickness, but rather sounds like an eating disorder. I know bringing up the subject can be touchy, but your brother needs to get his wife some counseling. At the very least, have him to talk to his wife's doctor about her eating (and purging) habits. Her purging will not only impact the health of the fetus, but her own health and potentially her ability to get pregnant with another child in the future.
I hope that the current pregnancy encounters no problems and you are blessed with a happy and healthy niece or nephew.
