Now, it appears that a producer of hers is at the root of the problem. Per TMZ:
Sources directly connected to Ke$ha tell us … it all started when the singer's “Get Sleazy” tour ended in 2011. She says [Dr.] Luke — who signed Ke$ha to a deal at age 18 — started ragging on her over the extra lbs she had gained in her downtime.
Ke$ha says Luke — a huge producer who has worked with Miley Cyrus and Rihanna — began calling Ke$ha fat and urged her management team to do something about it.
Our sources say Ke$ha complained … during a music video shoot in 2012 Luke told her she “looks like a f***ing refrigerator” … and the singer was profoundly affected by it.
What a douche. I am on the record as saying I think Ke$ha is beautiful. Call me when you get out. I love you.