Rat eating salt

Question
I have a 1yr old feeder rat, that was given to my son when the rat was 2mo.
I know very little about rats but have grow to my surprise very attached to him. He seems to have lost a bit of weight and has almost eaten all of a salt wheel in the last maybe 3wks that he has left untouched for the last six months. Should I be concerned, I feed him very well, lots of verity. Thank you :)

Answer
Yes, I would be concerned. I could not guess what his ailment might be. Sudden weight loss in spite of a good appetite, sudden behavior changes, and changes in food preferences, all warrant a trip to the vet for a check-up. Have you noticed whether or not his fluid intake has increase?