I think some of the loss when you are sick is due to dehydration. It's hard to drink enough liquids when you are sick and the fever and illness just take it outta you! But MY freinds lose weight when they are sick and do NOT gain it back. I just hate hearing them tell me about how they lost 6 lbs in 3 days because they were sick...and they don't gain it back! I gain weight when Im sick because I turn to comfort foods