Here are pics of Mr. Jobs after and before his weight loss:

Image courtesy Justin Sullivan/Getty Images

My guess: Steve Jobs has Celiac disease.  The effects of Celiac disease are that villi in the intenstine are unable to absorb nutrients.  This happens when a person with Celiac disease has gluten, which is a protein found in wheat, barley, and rye (some doctors may also recommend avoiding oats and other grains).  There is no cure, though the effects can be reversed simply by avoiding foods with gluten in them.

If Mr. Jobs does have Celiac disease, he would be able to get back to a “normal” weight simply by avoiding bread, cereal, certain sauces, and other products that contain wheat, barley, and rye.  My guess is that he would get back to his usual weight by late spring, just like the letter says.

Disclaimer: this is pure speculation on my part, and this is only my opinion based on my limited knowledge of celiac disease.  I am not a doctor of any sort, and I am not disclosing any private information about Mr. Jobs’ health.