Any topic suggestions for my senior project's persuasive research essay?

I am planning on doing weight training and eating a 'balanced diet' for my senior project, but I don't know what to write about for my research essay. The essay topic should be vaguely similar to what I'm doing for my senior project (it can even be about fast food or teen's eating habits), but it needs to persuasive and can't be on an obvious and well-accepted fact(I can't say "fast food is bad for you" or "eating a balanced diet is good for you"). The only thing I can think up of is to tackle the low carb diet craze (Atkins, South Beach) as unhealthy and that carbs are good for you. Any other suggestions? Thanks.