I usually ignore negative comments & change the subject, in real time. The hard part is not letting them get stuck in your head.
If someone is habitually negative I try to let their comments roll off my back. If it is someone who is generally not negative, I see if the negative comment might either have some degree of truth I don't want to face, OR if they could have meant well but accidentally put their foot in it.
Moms are hard. My mom means well and loves me but doesn't always know how to express it without sounding overly critical, and she's totally allergic to non-backhanded compliments. I try to remember she WANTS to help even though she's really actually very bad at helping. She really can't help it. Thankfully I have siblings who also see it.
The person who told you that they thought you were ill because of the weight loss could have been trying to express sympathy or offer help in what they perceived as your time of need. Sudden weight loss is a hallmark of many difficult diseases and/or their treatments, and maybe that person was genuinely trying to be helpful. They could also be someone who was trying to sabotage your self esteem. I'd have to know the person to be sure.
Keep focused on your own health and go for your goals!
My Sparkpage is set to private, but I'm open to SparkMail!
"People often say that motivation doesn't last. Well, neither does bathing--that's why we recommend it daily." - Zig Ziglar