basically, the only true staple is that we binge, then purge in some way after - be it vomiting(which can be done MANY different ways), starving or exercising aggressively after or taking things like laxatives and diuretics.
i would have added bad body image to that, but some people who are not bulimic or anorexic have problems with their images too
everything else changes for every person.
we all have different causes, triggers, binge foods and amounts.
also, not all bulimics and anorexics are skinny. it could be the 300 pound mom, the teenage boy with a little extra chub or it could be the bony 11 year old in grade 5.
bulimia does not discriminate against weight, age, gender, class or race
usually depression goes along with bulimia, whether your depressed when its starts, or after you realize your in too deep.