I agree with the
New York Times link from bloke (although I didn't read the entire thing).
I think it is more serious than a "hormonal imbalance". A "hormonal imbalance" is something women get once a month. If he has been losing weight steadily this entire year, wouldn't you think they would of found something as simple as a "treatable hormone imbalance" long ago, and got his weight back to a safe standard?
I love conspiracy theories and secretive happenings. In fact, I usually jump to that conclusion often. This time around, I'm thinking its smoke and mirrors. They may believe that Steve's failing health may lead to falling profits/sales, so they throw up a safe explanation.
I think there were several procedures of some kind that occurred during this past year, which may have THEN lead to loss proteins, causing him to lose weight. Whatever the procedures where, standard or serious, they kept it quiet, hoping he would bounce back quickly. It lead to unexpected circumstances, more questions, and finally an explanation. I DO believe he is better and will be recovering this year. Lets wish him well.