It really hit me this year that my 5yo male corn snake was obese. it didn't help that the fellows at the herp meeting laughed when they saw how huge it was! 
He's about 4 1/2 ft and used to be fed a jumbo mouse once a week. I really didn't think that was too much, but he's not a very active snake. Since Feb I cut him back to just a jumper/small mouse per week, even skipping a week on two different occasions (as opposed to the other suggestions I received that were to not feed him at all for a few months). He's also been "working out" as he is used in educational programs once or twice a month and is more active now, sometimes being on display for 3 hours at a time and held off and on while passers-by pet him.
This is what I am observing in him physically. He used to be completely smooth and fat all over with no real neck to speak of and some of his interstitial space between scales showing. Now he has a neck (YAY!) and his color has improved because of the lack of interstitial space and the overall closeness of his scales. On the the dorsal side of his length he is getting that "top of the bread loaf" look, but his ventral side is very mushy. When I held him today and really looked at him, I could easily feel his ribs sliding under my fingers. His behavior hasn't changed much; he's still pretty laid back, but more active because he's "hunting" once in a while now.
Here are my questions:
1) Is he too thin now and is that why I'm feeling his ribs?
2) Or is he still obese and that's why his underside is mushy?
3) How can improve his mushy tone?
4) How much should he be eating now?
Sorry this is so long, but this is a valuable snake to me and I'd like to get him in great shape.
Thanks,
Laura R (FL)
