To begin your speech, I think that you need to define what you are talking about, i.e. anorexia, and what you want to come out of this speech.
That said, you need to define what exactly anorexia is -- yes, it's an eating disorder, but it's actually a "mental" disorder, not a physical one, though it certainly has physical consequences. It primarily affects women, but men aren't immune to it. In fact, 10% of reported cases are by men. I think that the statistics are key, but what usually has the greatest impact is someone's personal story -- do you have anecdotes from your classmates or someone you know? Even if you won't name them, just the personal example is good. Maybe you could read a passage from one of the many books on this topic. When you conclude your talk, I think you need to make sure that you leave people with a message or an action -- like changing your own behavior is likely to change other peoples, etc.