I need to give my HR reasons why my surgery is necessary to apply for shared leave.

Are you just asking for the time off, or filling out FMLA paperwork? If your Dr fills out paperwork saying you need time off for medical reasons and FMLA is approved for you, I'm not sure HR would still be able to ask questions like this, but really not sure. If you're not, I'd recommend filling out the official paperwork.

My FMLA paperwork was pretty general, and didn't need to specify weight loss surgery. My surgeon's office just said "General Surgery" under specialty (which he is), and gave the frequency of follow-up appointments and any recovery time needed immediately following surgery. HR could easily figure out that I had weight loss surgery if they google my surgeon's name, but so far my HR rep has been really understanding and helpful!

HR has no legal right to know why you're having the surgery. Just that you are having it and can't work.

I work in Human Resources and no there is no need to let HR know the details, just the basics.. You need time off to have a procedure done.. they don't need to know details. It is really your decision to disclose that information, but just know you don't have to, and they shouldn't ask.

I work in HR also and they don't need to know those details.

My HR approved my FMLA leave but in order to request "shared leave" they needed more details. Even with details they denied my request. ?