"You're eating for two" may be a cute adage, but it shouldn't give you license to eat too much -- or the wrong foods ... Women who gain too little weight risk having a premature baby or one ...

"How many Weet-Bix can you eat?" one teenage boy asks his mates ... When is a lot of food too much? "Most boys gain about 20 kilograms in the four years of high school," Scrivin says.