80/20 - Really?

Did you know that a person's weight loss/gain is 80% to due with what a person eats? 

(I was told this today by a fitness expert)

80%!!!!!

I've been working my butt off with P90X and while I am attaining results it's nothing dramatic.

I don't eat poorly at at all but I do have my vices and "bad" foods I enjoy.

So that explains it.  Assuming you believe that, which I actually do.

Darn.