It's a wonder so many of you are worried about the medical. That should be of least worries as you can't really do much about your health at that point of time.
However, if your cholesterol is high, or blood sugar is high, or feel that there is anything wrong, do not apply yet. The medical can kill your application. If you fail that, SIA will not wait for you to get in shape. If you are already in the program, or advanced as a pilot, your status can be put on hold till you get back in shape like what SQ228 mentioned as it's CAAS ruling already and nothing to do with SIA's decision.
My advice, get yourself checked up first. Make sure you are fit and healthy. It would be a waste to get shown the door just because of a little problem.