You simply don't know what you are talking about. Cushing's disables the metabolism of proteins and fats, so even persons on severe diets become malnourished while still gaining weight.
Like you, medical professionals make the same assumptions about patients -- if they are fat, then they are eating too much or too much of the wrong thing. Many cases that is true. After suffering from Cushing's Disease for about 14 years, I typed all of my symptoms into Google and recognized my symptoms in the entries on Cushing's Disease. Then I went through several rounds of medical professionals to get the appropriate tests and diagnosis. Even after I had a diagnosis of Cushing's Disease, with a significant tumor revealed on the MRI, the surgeon I went to told me everything was in my head and I needed to get off the sofa and stop eating chips. My symptoms started to become life threatening a month later, and I went to MD Anderson in Houston for a second opinion. They have experts in pituitary diseases there and they diagnosed me over the course of a month, scheduling surgery a few weeks later. The day after surgery, they drew a blood sample to check my cortisol levels and they were absolutely normal instead of highly elevated. The assumptions that people made about me nearly killed me. My kidney function was so bad I was headed toward dialysis within six months. My heart palpitations had grown so frequent, I was a poor surgical risk by the time they finally operated. I almost certainly wouldn't be alive now if I had not fought to get an appropriate diagnosis and treatment.
You should read up on
Cushing's Disease in case you recognize it in someone else. Most doctors don't consider it because it is considered a rare disease. You may save a life.