Julia consumes huge meals throughout the day and then to prevent weight gain she hits the gym for hours of exercise each night. which type of eating disorder does julia most likely have?

The answer is nonpurging type bulimia nervosa.

In non-purging bulimia nervosa, the person uses different methods from normal to try compensating for binge episodes (eating huge meals), such as excessive exercising or fasting.  
Non-purging is different from purging because in purging, people induce their vomits or abuse of laxatives, diuretics, or enemas.