BMI is a method used to determine how much fat you are carrying. BMI of 35 is the limit for the licencing authorities to accept you without basicaly any questions.
BMI over 35 will be accepted, however, you most very probably will be asked to present a report from your Cardiologist and also a report from your Flight Testing Officer of your counties licencing authority, or from your Training Capt. or simulator instructor of the airline you work for, in that you have no problems of maniputaling the aircraft that you are on, and that you can perform all the emegency procedures without any difficulties. In Australia, a stress ECG is also asked for by CASA.
So, all being equal and you are in good health otherwise, then a BMI of over 35 is acceptable, BMI does not take into account your hereditary predisposition, its just a mathematical weight for height equation and that's it, so as some one said somewhere, maybe Arnie would fail the BMI test as muscle is heavier than fat.
p.s. I'm going on a diet after the festive season, as they (the authorities) are on my back over this as well...cheers.